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1
Jaske, Carl E., und R. Viswanathan. „Use of Miniature Specimens for Creep-Crack-Growth Testing“. Journal of Engineering Materials and Technology 122, Nr. 3 (16.03.2000): 327–32. http://dx.doi.org/10.1115/1.482814.
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Measuring the condition of high-temperature components after many years of service is an important part of remaining life assessment. Tests of miniature specimens have been utilized for this purpose because they require that only small samples be removed from the components, which minimizes or eliminates the need for costly repairs. Miniature-specimen techniques have been developed and validated for creep-rupture testing but not for creep-crack-growth testing. The objective of this research was to develop and validate a procedure for measuring creep-crack-growth behavior using miniature specimens. Based on a past study of Type 316 stainless steel, the single-edge-notch-tension (SENT) specimen configuration was chosen for the current work. SENT specimens were designed and prepared from both base metal and weldments of 2-1/4Cr-1Mo and 1-1/4Cr-1/2Mo steels. The base metal was ASME SA 387, Grade P22 and Grade P11 plate, respectively. The 2-1/4Cr-1Mo steel weldment was a seam-weld hot reheat steam pipe that had been in service for 106,000 hours, while the 1-1/4Cr-1/2Mo steel weldment was from a pipe that had been weld repaired after 244,200 hours of service. SENT specimens with test sections of 10×5×1.5 mm, 15×7.5×1.5 mm, and 20×10×1.5 mm were evaluated. Tests were conducted under constant weight loading or constant load-line displacement loading. Specimens were heated to 538°C using a standard laboratory furnace. Crack length was measured using the DC electric potential drop method. The test results were analyzed to produce creep-crack-growth rate da/dt as a function of the C* integral and compared with data from tests of half-size (1/2T-CT) and standard full-size (1T-CT) compact-tension specimens. For both base metals, the 1/2T-CT and three sizes of SENT specimens gave results that agreed well with those of 1T-CT specimens. For the 2-1/4Cr-1Mo steel weldments, SENT specimens produced good results. However, SENT specimens of the 1-1/4Cr-1/2Mo steel weldments exhibited cracking blunting and no creep crack growth. The reasons for the differences in behavior are discussed and guidance for application of miniature specimens to creep-crack-growth testing is presented. [S0094-4289(00)01403-1]
2
Swaminathan, V. P., N. S. Cheruvu und A. Saxena. „Life Assessment of an HP-IP Rotor Under Creep Service Conditions“. Journal of Engineering for Gas Turbines and Power 112, Nr. 2 (01.04.1990): 237–42. http://dx.doi.org/10.1115/1.2906169.
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A CrMoV high and intermediate-pressure (HP-IP) rotor exhibited in-service cracking in the blade groove walls. Cracks initiated from a notch and propagated under creep conditions to a depth of 0.255 in. (6.5 mm). Since the unit was base loaded, the contribution of cyclic loading (startups and shutdowns) was not significant. The total life of the groove walls is predicted by applying a life prediction approach that accounts for both crack initiation and propagation. Crack initiation life is based on short-term creep tests extrapolated to long times using a time-temperature parameter. Crack propagation time is estimated using a newly developed time-dependent fracture mechanics concept. A parameter Ct is used to express the crack growth rate under creep loading conditions. Pertinent material properties such as creep deformation and creep crack growth rate were obtained by testing the material from the subject rotor. The results obtained by this analysis show that about 50 percent of the estimated life was spent in crack propagation. Predicted service life time compares very favorably with the actual operating life of the rotor.
3
Merah, N. „Notch-Strengthening Phenomenon Under Creep-Fatigue Loading Conditions“. Journal of Pressure Vessel Technology 122, Nr. 1 (11.10.1999): 15–21. http://dx.doi.org/10.1115/1.556140.
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A study of the notch and frequency effects on fatigue life at high temperature is carried out using notched and unnotched plate specimens of SS 304 under stress-controlled testing conditions. Analysis of the σ-Nf results obtained at 600°C under fatigue and creep-fatigue conditions allowed the generalization of the σ-Nf-Kt relation proposed in an earlier study. Examinations of the experimental data with hold-time testing suggested that in these conditions, the frequency effect should be incorporated in the relationship. Results obtained from the modified relation are in agreement with the experimental data, within a factor of two. Finite element analysis was carried out to determine the state of stresses and strains at the notch root by simulating four creep-fatigue cycles. The computed results indicated that, under zero-to-tension cyclic loading with controlled nominal stress, the maximum local stress at the notch root relaxes; this results in a minimum local stress in compression, and as a consequence, the mean local stress is significantly reduced. The stress relaxation as well as the creep strain accumulation were found to occur only in the vicinity of the notch (within 0.75 mm). The numerical results concerning the local stress relaxation and the time-dependent strain accumulation are used to explain the notch-strengthening effect on life observed in the present study. [S0094-9930(00)00401-7]
4
Griffin, D. S., A. K. Dhalla und W. S. Woodward. „Validation of Inelastic Analysis by Full-Scale Component Testing“. Journal of Pressure Vessel Technology 109, Nr. 1 (01.02.1987): 42–49. http://dx.doi.org/10.1115/1.3264854.
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This paper compares theoretical and experimental results for full-scale, prototypical components tested at elevated-temperatures to provide validation for inelastic analysis methods, material models, and design limits. Results are discussed for piping elbow plastic and creep buckling, creep ratcheting, and creep relaxation; nozzle creep ratcheting and weld cracking; and thermal striping fatigue. Comparisons between theory and test confirm the adequacy of components to meet design requirements, but identify specific areas where life prediction methods could be made more precise.
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FERDOUS, IMAM UL, NASRUL AZUAN ALANG, Juliawati Alias und Suraya Mohd Nadzir. „Numerical Prediction of Creep Rupture Life of Ex-Service and As-Received Grade 91 Steel at 873 K“. International Journal of Automotive and Mechanical Engineering 18, Nr. 3 (19.09.2021): 8845–58. http://dx.doi.org/10.15282/ijame.18.3.2021.01.0678.
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Infallible creep rupture life prediction of high temperature steel needs long hours of robust testing over a domain of stress and temperature. A substantial amount of effort has been made to develop alternative methods to reduce the time and cost of testing. This study presents a finite element analysis coupled with a ductility based damage model to predict creep rupture time under the influence of multiaxial stress state of ex-service and as-received Grade 91 steel at 873 K. Three notched bar samples with different acuity ratios of 2.28, 3.0 and 4.56 are modelled in commercial Finite Element (FE) software, ABAQUS v6.14 in order to induce different stress state levels at notch throat area and investigate its effect on rupture time. The strain-based ductility exhaustion damage approach is employed to quantify the damage state. The multiaxial ductility of the material that is required to determine the damage state is estimated using triaxiality-ductility Cock and Ashby relation. Further reduction of the ductility due to the different creep mechanisms over a short and long time is also accounted for in the prediction. To simulate the different material conditions: ex-service and as-received material, different creep coefficients (A) have been assigned in the numerical modelling. In the case of ex-service material, using mean best fit data of minimum creep strain rate gives a good life prediction, while for new material, the lower bound creep coefficient should be employed to yield a comparable result with experimental data. It is also notable that ex-service material deforms faster than as-received material at the same stress level. Moreover, higher acuity provokes damage to concentrate on the small area around the notch, which initiates higher rupture life expectancy. It also found out that, the stress triaxiality and the equivalent creep strain influence the location of damage initiation around the notch area.
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Beech, S. H., und E. Q. Clutton. „Interpretation of results of full notch creep test and comparison with notched pipe test“. Plastics, Rubber and Composites 34, Nr. 7 (September 2005): 294–300. http://dx.doi.org/10.1179/174328905x59791.
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7
Dennies, Daniel P., und Robert Kupkovits. „Room-Temperature Creep Testing of Grade 2 CP Titanium Plate Using Notch Tensile Samples“. Journal of Failure Analysis and Prevention 14, Nr. 4 (24.05.2014): 437–42. http://dx.doi.org/10.1007/s11668-014-9831-5.
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8
Pinter, Gerald, Markus Haager und Reinhold W. Lang. „Influence of nonylphenol–polyglycol–ether environments on the results of the full notch creep test“. Polymer Testing 26, Nr. 6 (September 2007): 700–710. http://dx.doi.org/10.1016/j.polymertesting.2007.01.010.
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9
Fleissner, M. „Experience with a full notch creep test in determining the stress crack performance of polyethylenes“. Polymer Engineering & Science 38, Nr. 2 (Februar 1998): 330–40. http://dx.doi.org/10.1002/pen.10194.
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Hyde, C. J., Thomas H. Hyde und Wei Sun. „Small Ring Testing of High Temperature Materials“. Key Engineering Materials 734 (April 2017): 168–75. http://dx.doi.org/10.4028/www.scientific.net/kem.734.168.
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In service components such as steam pipes, pipe branches, gas and steam turbine blades, etc. which operate in engineering applications such as power plant, aero-engines, chemical plant etc., can operate at temperatures which are high enough for creep to occur. Often, only nominal operating conditions (i.e. pressure, temperatures, system load, etc.) are known and hence precise life predictions for these components, which may be complex in terms of geometry or weld characteristics, are not possible. Within complex components it can also be the case that the proportion of the material creep life consumed may vary from position to position within the component. It is therefore important that non-destructive techniques are available for assisting in the making of decisions on whether to repair, continue operating or replace certain components. Small specimen creep testing is a technique which can allow such analyses to be performed. Small samples of material are removed from the component to make small creep test specimens. These specimens can then be tested to give information on the remaining creep life of the component. This paper presents the results of small ring specimens tested under creep conditions and shows the comparison to standard (full size) creep testing for materials used under high temperature in industry.
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Fuji, Akio, Masaaki Tabuchi, A. Toshimitsu Yokobori und Takeo Yokobori. „Influence of notch shape and geometry during creep crack growth testing of TiAl intermetallic compounds“. Engineering Fracture Mechanics 62, Nr. 1 (Januar 1999): 23–32. http://dx.doi.org/10.1016/s0013-7944(98)00080-0.
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12
Dennies, Daniel P., und Robert Kupkovits. „Extended Room-Temperature Creep Testing of Grade 2 CP Titanium Plate Using Notch Tensile Samples“. Journal of Failure Analysis and Prevention 16, Nr. 1 (04.01.2016): 4–8. http://dx.doi.org/10.1007/s11668-015-0047-0.
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13
Sprince, Andina, Tomass Kozlovskis, Rihards Gailitis, Juozas Valivonis, Kinga Korniejenko und Arnaud Castel. „Tensile Creep of Cement and Concrete Composites: Monitoring by Means of 2D-Digital Image Correlation“. Applied Sciences 11, Nr. 18 (08.09.2021): 8334. http://dx.doi.org/10.3390/app11188334.
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Creep and shrinkage of Cement and Concrete Composites (CCC) are significant properties that need to be considered to use these materials in practice. Many previous scientific studies revealed CCC creep characteristics under sustained compression and shrinkage, using traditional test methods from design standards. Because of the complexity of experimental procedures, CCC creep in tension has not been studied as close. Furthermore, there is no unified standard that proposes applicable testing methods or specific testing apparatus. This study examines the suitability of 2D—Digital Image Correlation (DIC) to observe the creep deformations of specimens under tension. Ordinary Portland cement (OPC) mortar with 1% polyvinyl alcohol (PVA) fibres has been investigated in the research. Compact tension (CT) specimens 150 × 150 × 12 mm (with a notch) were used. Creep deformations under sustained uniaxial tension (applied loading corresponding to 60% of the ultimate strength) were measured. DIC images were captured using an entry/mid-level DSLR camera. Results show that DIC is suitable for studying uniaxial tensile creep of cement and concrete composites. Deformation of specimens in tension was similar to that measured using the conventional method (using surface-attached gauges).
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Narasimhachary, Santosh B., Kanwardeep S. Bhachu, Sachin R. Shinde, Phillip W. Gravett und James C. Newman. „A single edge notch specimen for fatigue, creep-fatigue and thermo-mechanical fatigue crack growth testing“. Engineering Fracture Mechanics 199 (August 2018): 760–72. http://dx.doi.org/10.1016/j.engfracmech.2017.08.011.
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15
Arezoumandi, Mahdi, Mark Ezzell und Jeffery S. Volz. „Development and Testing of Chemically-Based Self-Consolidating Concrete“. Applied Mechanics and Materials 174-177 (Mai 2012): 11–17. http://dx.doi.org/10.4028/www.scientific.net/amm.174-177.11.
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Self-consolidating concrete (SCC) has the potential to significantly reduce costs associated with concrete construction. SCC is a highly flowable, nonsegregating concrete that has a variety of advantages over conventional concrete (CC). However, SCC is not without its problems, which can include increased creep and shrinkage, as well as decreased bond and shear strength. The goal of this research project was to evaluate the creep, shrinkage, and shear behavior of a chemically-based SCC mix. One of the benefits of a chemically-based approach is the potential to eliminate the negative side effects of many SCC mixes. The investigation included development of the mix design, construction and testing of creep and shrinkage specimens, and construction and testing of full-scale beam specimens to evaluate the shear behavior. The results indicate that a chemically-based SCC performs as well or better than conventional portland-cement concrete.
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Duan, Xiaochang, Hongwei Yuan, Wei Tang, Jingjing He und Xuefei Guan. „A Phenomenological Primary–Secondary–Tertiary Creep Model for Polymer-Bonded Composite Materials“. Polymers 13, Nr. 14 (18.07.2021): 2353. http://dx.doi.org/10.3390/polym13142353.
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This study develops a unified phenomenological creep model for polymer-bonded composite materials, allowing for predicting the creep behavior in the three creep stages, namely the primary, the secondary, and the tertiary stages under sustained compressive stresses. Creep testing is performed using material specimens under several conditions with a temperature range of 20 °C–50 °C and a compressive stress range of 15 MPa–25 MPa. The testing data reveal that the strain rate–time response exhibits the transient, steady, and unstable stages under each of the testing conditions. A rational function-based creep rate equation is proposed to describe the full creep behavior under each of the testing conditions. By further correlating the resulting model parameters with temperature and stress and developing a Larson–Miller parameter-based rupture time prediction model, a unified phenomenological model is established. An independent validation dataset and third-party testing data are used to verify the effectiveness and accuracy of the proposed model. The performance of the proposed model is compared with that of an existing reference model. The verification and comparison results show that the model can describe all the three stages of the creep process, and the proposed model outperforms the reference model by yielding 28.5% smaller root mean squared errors on average.
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Funahashi, Miki, und Walter T. Young. „Cathodic Protection of Prestressed Bridge Members—Full-Scale Testing“. Transportation Research Record: Journal of the Transportation Research Board 1561, Nr. 1 (Januar 1996): 13–25. http://dx.doi.org/10.1177/0361198196156100103.
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The results of a study on the use of cathodic protection on prestressed and post-tensioned concrete bridge members are summarized. Previous laboratory tests to evaluate hydrogen embrittlement of high strength steel embedded in concrete have proven that cathodic protection will generate hydrogen on high-strength steel in concrete if the potential is more negative than the thermodynamic hydrogen evolution potential. The hydrogen generated will enter the steel and cause a loss in ductility that will adversely affect the steel's performance if a notch is present. Full-scale beams were constructed to further study those phenomena. Four pretensioned beams were constructed. In addition, two post-tensioned slabs were constructed to evaluate cathodic protection of anchorages and tendons encased in metal or plastic conduits. Cathodic protection currents were supplied by IR drop-free potential controlled rectifiers. Good potential control at control points was achieved by using externally mounted silver-silver chloride reference electrodes and a conductive gel bridge. However, inconsistent potential control occurred at locations other than at the control points. Later in the study, constant current power supplies were used on two of the beams. Hydrogen entering the steel as the result of corrosion appears to have masked the presence of hydrogen that might have been produced by cathodic protection. The analysis also revealed that there was corrosion of some pretensioned wires at crossings with interior steel reinforcing bars due to interference (stray current) caused by cathodic protection application. Analysis of the post-tensioned slabs indicated little effect of cathodic protection on tendons inside plastic or metal ducts from the application of cathodic protection. Beneficial effects were noted on anchor points where mortar was in contact with the metal.
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Mishnev, Roman, Nadezhda Dudova, Rustam Kaibyshev und Andrey Belyakov. „On the Fracture Behavior of a Creep Resistant 10% Cr Steel with High Boron and Low Nitrogen Contents at Low Temperatures“. Materials 13, Nr. 1 (18.12.2019): 3. http://dx.doi.org/10.3390/ma13010003.
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An advanced, high chromium, creep-resistant steel was subjected to the tensile tests and three-point bending tests of Charpy V-notch specimens at temperatures of −196 to 20 °C. The steel exhibited ductile fracture under tension tests at all of the temperatures studied. The mechanical properties, i.e., strength and uniform elongation, were enhanced with a decrease in temperature down to −140 °C. Transgranular, dimpled fracture remained the primary fracture mechanism under tension. On the other hand, the results obtained with Charpy V-notch specimens suggested the ductile–brittle transition (DBT). Full embrittlement was observed at temperatures of −60 °C and −150 °C upon impact tests and three-point bending tests, respectively, when the unstable crack started to propagate without remarkable plastic deformation. The DBT temperature of −27 °C for the present steel corresponded to the 28 J impact transition temperature, T28J, when the maximum impact stress matched the maximal true tensile stress.
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Thuy, Maximilian, Ute Niebergall, Harald Oehler, Ingo Alig und Martin Böhning. „Evaluation of the damaging effect of crop protection formulations on high density polyethylene using the Full Notch Creep Test“. Polymer 228 (Juli 2021): 123853. http://dx.doi.org/10.1016/j.polymer.2021.123853.
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20
Barbera, Daniele, und Haofeng Chen. „On the Plastic Strain Accumulation in Notched Bars During High-Temperature Creep Dwell“. Journal of Mechanics 36, Nr. 2 (21.02.2020): 167–76. http://dx.doi.org/10.1017/jmech.2019.56.
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ABSTRACTStructural integrity plays an important role in any industrial activity, due to its capability of assessing complex systems against sudden and unpredicted failures. The work here presented investigates an unexpected new mechanism occurring in structures subjected to monotonic and cyclic loading at high temperature creep condition. An unexpected accumulation of plastic strain is observed to occur, within the high-temperature creep dwell. This phenomenon has been observed during several full inelastic finite element analyses. In order to understand which parameters make possible such behaviour, an extensive numerical study has been undertaken on two different notched bars. The notched bar has been selected due to its capability of representing a multiaxial stress state, which is a practical situation in real components. Two numerical examples consisting of an axisymmetric v-notch bar and a semi-circular notched bar are considered, in order to investigate different notches severity. Two material models have been considered for the plastic response, which is modelled by both Elastic-Perfectly Plastic and Armstrong-Frederick kinematic hardening material models. The high-temperature creep behaviour is introduced using the time hardening law. To study the problem several results are presented, as the effect of the material model on the plastic strain accumulation, the effect of the notch severity and the mesh element type and sensitivity. All the findings further confirm that the phenomenon observed is not an artefact but a real mechanism, which needs to be considered when assessing off-design condition. Moreover, it might be extremely dangerous if the cyclic loading condition occurs at such a high loading level.
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Saber, M., D. W. J. Tanner, W. Sun und T. H. Hyde. „Determination of creep and damage properties for P92 at 675 °C“. Journal of Strain Analysis for Engineering Design 46, Nr. 8 (13.09.2011): 842–51. http://dx.doi.org/10.1177/0309324711413012.
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In order to predict the service life of components that operate at high temperatures, such as steam carrying pipes in conventional power plants, the material creep behaviour needs to be determined. There are little creep data available on grade P92 (9Cr2W) steel (a potential successor to P91) as it is a relatively new material; therefore a testing programme has been undertaken. This paper presents the results of uniaxial and notched bar creep tests on P92 parent material (PM) and P92 weld metal (WM) at 675 °C. The PM had higher failure times and lower minimum creep strain rates for tests in the same stress range (80–100 MPa) as the WM, but the PM and WM values tend to converge at high stress, with a significant difference between the failure times as applied stress decreases. The notch strengthening effect was found to decrease as the applied stress decreased. Processing of the test data including the calculation of the minimum creep strain rates has been performed to determine the material constants required for Norton’s steady state creep and both the Kachanov and the Liu and Murakami creep damage models. Material constant sets for creep of P92 PM and WM at 675 °C, including a parameter to describe the effect of a multiaxial stress state, have been obtained that give a good fit to the test data. Validation was achieved using finite element analysis.
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Liu, Hao, Rui Bao und Bin Jun Fei. „Determination of Creep Crack Growth Threshold by Experiments under Elevated Temperature with Pre-Stressed Specimens“. Advanced Materials Research 891-892 (März 2014): 371–76. http://dx.doi.org/10.4028/www.scientific.net/amr.891-892.371.
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A novel test method is presented in this paper for determination of the creep crack growth threshold. In this method, a wedge is placed in the notch of a standard compact tension (CT) specimen with a pre-crack, which provides an evaluable stress fields characterized with stress intensity factor (K) at the crack tip. Then the specimen is kept in the test temperature for a certain time. The creep crack growth threshold of the material at a given temperature can be obtained by extrapolating the curves of the crack growth rate vs.Kin the double logarithmic coordinates. Since it does not need mechanical testing machine and several specimens can be tested simultaneously, the proposed method is economical in both costs and time. Tests on a nickel-based powder metallurgy superalloy FGH97 are conducted using this method at 600°C, 650°C and 750°C, which indicate its feasibility.
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Guo, Long, und Xing Zhong Zhang. „Positive Effects of High-Temperature Steel Creep Behavior on Continuous Casting Slab“. Key Engineering Materials 723 (Dezember 2016): 103–10. http://dx.doi.org/10.4028/www.scientific.net/kem.723.103.
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Mechanical properties and creep behavior of continuous casting slab subjected to uniaxial tensile tests at 1100 and 1150 °C were considered in this paper. All of specimens was given a typical in-situ melting thermal history and interrupted cooling cycle before testing. An increase in load and temperature accelerates the creep rate thereby decreasing the steady state range. A new creep equation whose parameters are calculated by inverse-estimation using the regression analysis was proposed based on Norton-Bailey creep law. Primary and secondary creep stages could be described accurately by the new equation. Positive creep effects on straightening technology in continuous casting slab were presented in this paper. Involute continuous straightening technology could give full play to the role of steel creep deformation at high temperature. This research is helpful for the design of the new casting machine and improvement of old casting machine in using depended on high temperature creep behavior.
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Shingledecker, J. P., und G. M. Pharr. „Testing and Analysis of Full-Scale Creep-Rupture Experiments on Inconel Alloy 740 Cold-Formed Tubing“. Journal of Materials Engineering and Performance 22, Nr. 2 (03.07.2012): 454–62. http://dx.doi.org/10.1007/s11665-012-0274-4.
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Yang, Dayong, Hamid Reza Karimi und Mohammad Reza Mohammad Aliha. „Comparison of Testing Method Effects on Cracking Resistance of Asphalt Concrete Mixtures“. Applied Sciences 11, Nr. 11 (31.05.2021): 5094. http://dx.doi.org/10.3390/app11115094.
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As an inherent characteristic of materials, the fracture toughness is an important parameter to study the cracking behavior of asphalt concrete mixtures. Although material compositions and environmental conditions have a significant effect on the fracture toughness, for a certain material and testing environment, the test condition including the specimen configuration and loading type may also affect the obtained fracture toughness. In this paper, the effect of specimen configuration and applied loading type on the measured pure mode-I fracture toughness (KIc) is investigated. In order to achieve this purpose, using a typical asphalt mixture, four different test specimens including Semi-Circular Bend (SCB), Edge Notch Disc Bend (ENDB), Single Edge Notch Beam (SENB) and Edge Notch Diametral Compression (ENDC) disc are tested under pure mode I. The mentioned specimens have different shapes (i.e., full disc, semi-disc and rectangular beam) and are loaded either with symmetric three-point bending or diametral compressive force. The tests were performed at two low temperatures (−5 °C and −25 °C) and it was observed that the critical mode-I fracture toughness (KIc) was changed slightly (up to 10%) by changing the shape of the test specimen (i.e., disc and beam). This reveals that the fracture toughness is not significantly dependent on the shape of the test specimen. However, the type of applied loading has a significant influence on the determined mode I fracture toughness such that the fracture toughness determined by the disc shape specimen loaded by diametral compression (i.e., ENDC) is about 25% less than the KIc value with the same geometry but loaded with the three-point bending (i.e., ENDB) specimen. In addition, the fracture toughness values of all tested samples were increased linearly by decreasing the test temperature such that the fracture toughness ratio (KIc (@−25 °C)/KIc (@−5 °C)) was nearly constant for the ENDB, ENDC, SCB and SENB samples.
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Asyraf, M. R. M., M. R. Ishak, S. M. Sapuan, N. Yidris, R. A. Ilyas, M. Rafidah und M. R. Razman. „Evaluation of Design and Simulation of Creep Test Rig for Full-Scale Crossarm Structure“. Advances in Civil Engineering 2020 (30.04.2020): 1–10. http://dx.doi.org/10.1155/2020/6980918.
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A simulated model was developed in order to design and simulate the mechanical properties of a cantilever beam creep testing rig for a full-scale size crossarm in transmission towers. Currently, the Malaysian power grid system is implementing several materials, such as Chengal wood, polymeric composite, and galvanised steel, as crossarm structures. However, there is a lack of study regarding the long-term mechanical behaviour of heavy structures in the literature. Hence, this article explains the design development of creep test rig for a full-scale crossarm structure using CATIA and mechanical simulation (deformation and safety factors) of the product via ANSYS. The test rig will be used to predict the creep life of the cantilever beam structure. In this study, a tall and large base area structure was designed and replicated from an actual tower to elevate the crossarm above the ground level. In order to select the best performance model, a baseline conceptual test rig was generated in CAD modelling, and the finite element analysis was carried out by using a static structural analysis in ANSYS. Four different bracing configurations were incorporated in the baseline model, and the modified structures were then analysed. The results show that the hybrid bracing configuration has enhanced the mechanical properties and safety factors in the baseline model.
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Bachanova, Veronika, Valarie McCullar, Rosanna Wangen und Jeffrey S. Miller. „Notch Activation in Cord Blood Progenitors Induces a CD7+ Common NK/T Precursor Capable of NK Cell Commitment without Full Maturation and Differentiation of Lineage Committed Pre-T Lymphocytes with a Th1 Phenotype.“ Blood 108, Nr. 11 (16.11.2006): 644. http://dx.doi.org/10.1182/blood.v108.11.644.644.
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Abstract Activation of Notch signaling regulates differentiation and homeostasis of hematopoetic stem cells. After stimulation, intracellular Notch is proteolytically released and by binding the CSL complex and co-activator MAML, and initiates transcription of downstream genes. We hypothesize that Notch is important for distinct stages of lymphoid development. Human cord blood CD34+ progenitor cells were transduced with retrovirus based eGFP-control, eGFP-Notch and Notch Dominant Negative/MAML (eGFP-DN) constructs. CD34+/eGFP+ were sorted and then co-cultured with the mouse embryonic liver cell line EL08.1D2 and exogenous human cytokines (IL-3. IL-7, IL-15, Flt3 ligand and c-kit ligand). As early as 48 hours after transduction, CD34+/Notch+ cells gave rise to population of lymphoid precursors CD34+CD7+CD10- (42±5% of all cells) while essentially no cells with this phenotype were detected with the control or DN construct. Proliferation of eGFP-Notch transduced cells in a 6-day thymidine incorporation assay was higher compared to eGFP-DN transduced cells (8410±839 vs. 1103±209 cpm; n=3; p=0.00005). Within 7 days 11±1.5% NK emerged from CD34+/Notch+cells compared to 0.8±0.2% of CD34+/eGFP+ control cells (n=5, p=0.0001). NK cell generation peaked at day 28 with a significantly higher expression of CD7 on NK cells (Notch: 75±5% vs. eGFP: 4.5±1%, n=5, p=0.00004), and no B lymphocytes were seen. Analysis of Notch induced NK cells demonstrated early expression of L-selectin and increased expression of CD45RA on all lymphoid progenitors. At 4 weeks, functional testing revealed reduced cytotoxicity against K562 (Notch: 37±0.5% vs. eGFP: 63.5±1.3%; n=7, p=0.007) suggesting immature function. CD34+/Notch+ derived NK lymphocytes also showed diminished acquisition of the lectin-type receptor NKG2A (Notch: 8.3±3% vs. eGFP: 27.4±4.5%; p=0.04) and killer immunoglobulin receptors (Notch: 2.2±0.5% vs. eGFP: 10.8±4: p=0.05). We next asked whether the Notch induced CD7+ precursor was NK restricted or a common NK/T cell precursor. After 5 weeks in culture, a distinct population of CD3+ T-cells emerged (Notch: 18±5% vs. eGFP: 1.6±0.2; n=5, p<0.001%) which were CD4 and CD8 negative and did not express surface TCR a/b or g/d, but expressed high levels pre-T-alpha mRNA. These Notch activated cells were bona fide T-cells based on their capacity to produce IL-2 after PMA/Ca/I stimulation (62.4±4% by intracellular staining) while essentially no IL-2 production occurred from eGFP control cells (1.6±0.2%; p<0.0001). T-cell development was dependent on both Notch and the EL08.1D2 as no T-cells resulted from CD34+/eGFP-Notch in the absence of stroma. These findings suggest that in addition to Notch and exogenous cytokines, other soluble factors are required for T cell development. In conclusion, our data showed that activated Notch pathway leads to differentiation of a common CD7+ lymphoid precursor capable of both early NK cell and T-cell differentiation. This suggests that differences in Notch ligands in local microenvironments (marrow, thymus, lymph node) may be an important mechanism to orchestrate NK and T cell development.
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Wang, Jichang, Xiaoming Guo und Nailong Zhang. „Study of the progressive failure of concrete by phase field modeling and experiments“. International Journal of Damage Mechanics 30, Nr. 9 (24.03.2021): 1377–99. http://dx.doi.org/10.1177/10567895211001410.
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In this research, experiments and numerical simulations are employed to research the failure process of concrete. Fracture experiments on three-point bending (TPB) concrete beams with a prefabricated edge notch at the middle of the beam bottom are performed using a modified rigid testing instrument. The characteristics of the crack and section are analyzed, including the crack tensile opening displacement, crack length and width, and crack faces characteristics. Also, the full curves of the force-crack tensile opening displacement (CMOD) and force-deflection of the TPB beams with the prefabricated edge notch after breakage are obtained. The phase field (PF) damage model is applied to the mixed-mode and mode-I failure processes of concrete structures through the ABAQUS subroutine user defined element (UEL). The crack path and the full curves of force-CMOD and force-deflection obtained by numerical calculations are consistent with the experimental results and the calculated results of other researchers. The influences of the mesh sizes, initial lengths, and notched depths on the TPB beam of concrete are also analyzed.
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Stückelschweiger, Gruber, Jin und Harmuth. „Wedge-Splitting Test on Carbon-Containing Refractories at High Temperatures“. Applied Sciences 9, Nr. 16 (08.08.2019): 3249. http://dx.doi.org/10.3390/app9163249.
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The mode I fracture behavior of ordinary refractory materials is usually tested with the wedge-splitting test. At elevated temperatures, the optical displacement measurement is difficult because of the convection in the furnace and possible reactions of refractory components with the ambient atmosphere. The present paper introduces a newly developed testing device, which is able to perform such experiments up to 1500 °C. For the testing of carbon-containing refractories a gas purging, for example, with argon, is possible. Laser speckle extensometers are applied for the displacement measurement. A carbon-containing magnesia refractory (MgO–C) was selected for a case study. Based on the results obtained from tests, fracture mechanical parameters such as the specific fracture energy and the nominal notch tensile strength were calculated. An inverse simulation procedure applying the finite element method yields tensile strength, the total specific fracture energy, and the strain-softening behavior. Additionally, the creep behavior was also considered for the evaluation.
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Schilling, Markus, Ute Niebergall und Martin Böhning. „Full notch creep test (FNCT) of PE-HD – Characterization and differentiation of brittle and ductile fracture behavior during environmental stress cracking (ESC)“. Polymer Testing 64 (Dezember 2017): 156–66. http://dx.doi.org/10.1016/j.polymertesting.2017.09.043.
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Hyde, T. H., W. Sun und J. A. Williams. „Creep analysis of pressurized circumferential pipe weldments—a review“. Journal of Strain Analysis for Engineering Design 38, Nr. 1 (01.01.2003): 1–27. http://dx.doi.org/10.1243/030932403762671854.
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This paper reviews work related to the high-temperature creep analysis of pressurized circumferential pipe weldments. It is important to define the problem and thus metallurgical features correctly; the identification of material microstructural-property variations within the heat-affected zone (HAZ) and the failure modes of welds are briefly included, as well as in-service experience of pipe welds. Experimental methods, including model and full-size component testing, are summarized and examples of typical tests results are described. Material constitutive equations, which can be used in describing the creep deformation of and failure mechanisms in welds, are briefly described. Numerical modelling using finite element (FE) methods, covering a range of approaches and analyses, taking account of the effects of material properties, pipe geometry, weld dimensions and system loading, on the stresses and failure behaviour of pipe weldments, are summarized. Typical results are presented to illustrate the potential uses and limitations of the FE methods.
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Schilling, M., M. Böhning, H. Oehler, I. Alig und U. Niebergall. „Environmental stress cracking of polyethylene high density (PE-HD) induced by liquid media - Validation and verification of the full-notch creep test (FNCT)“. Materialwissenschaft und Werkstofftechnik 48, Nr. 9 (September 2017): 846–54. http://dx.doi.org/10.1002/mawe.201700065.
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Dhalla, A. K. „Influence of Weld Factors on Creep-Rupture Cracking at Elevated Temperature“. Journal of Pressure Vessel Technology 113, Nr. 2 (01.05.1991): 194–209. http://dx.doi.org/10.1115/1.2928747.
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The purpose of this paper is to identify the weld effects which are of primary importance in elevated temperature design. A full-scale Fast Flux Test Facility (FFTF) Intermediate Heat Exchanger (IHX) was tested at Westinghouse to investigate weld effects at elevated temperature. The IHX was subjected to two and a half times the design pressure. In addition, one of the four welded nozzles of the IHX was subjected to 26 severe thermal downshock transients, which were interspersed with 156 hr of creep hold time at 1100°F (593°C). At the end of testing, creep rupture cracks were observed in the weldments at the nozzle to cylinder intersections, whether or not they experienced downshock transients. Detailed three-dimensional inelastic analyses were performed to investigate the effects of welding on the creep-rupture strength of weldments. The analyses suggest that the weldment material property variation contributed to creep-rupture cracking at high primary pressure loading. The weld metal and heat-affected zone had higher yield strength, but lower creep ductility compared to the nozzle base material. The analytical predictions and metallurgical observations suggest that the role of residual stresses on creep-rupture cracking is of secondary importance, and need not be numerically simulated in the elevated temperature design of weldments.
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Craine, R. E., und T. D. Hawkes. „On the creep of ferritic weldments containing multiple zones in plates under uniaxial loading“. Journal of Strain Analysis for Engineering Design 28, Nr. 4 (01.10.1993): 303–9. http://dx.doi.org/10.1243/03093247v284303.
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Weldments are not currently included in most high temperature design codes although welds are known to be life-limiting. Metallurgists state that there are four principal regions in a ferritic weldment with the parent metal and weld region being separated by both the narrow high temperature heat affected zone (HAZ) and the narrow lower temperature type IV region. Expected weld performance can be evaluated using full size weldment testing or by the simpler creep testing of cross-weld specimens in the laboratory. The former is expensive but the latter, although cheaper to carry out, is not well understood. To improve understanding of the failure process in weldments, a plate containing these four distinct weldment regions and subjected to a constant uniaxial tensile end loading is studied in this paper. The plate is modelled using the Cosserat theory of plates and a generalization of the steady state Norton creep law and numerical solutions of the governing differntial equations are obtained illustrating how the creep strain rate is changed by variations in the widths and strengths of the type IV, HAZ, and weld regions and by varying the creep index. These results reveal that when narrow zones exist in a ferritic weldment the strain rate at a point can be greatly affected by the properties of both the neighbouring regions and non-adjacent zones and, therefore, deductions made through using only the homogeneous strengths of the constitutent materials would usually be incorrect.
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Asyraf, M. R. M., M. R. Ishak, S. M. Sapuan und N. Yidris. „Conceptual design of creep testing rig for full-scale cross arm using TRIZ-Morphological chart-analytic network process technique“. Journal of Materials Research and Technology 8, Nr. 6 (November 2019): 5647–58. http://dx.doi.org/10.1016/j.jmrt.2019.09.033.
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Horvath, Robert G., und K.-J. Chae. „Long-term settlement of model rock-socketed piers“. Canadian Geotechnical Journal 26, Nr. 3 (01.08.1989): 348–58. http://dx.doi.org/10.1139/t89-049.
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Very little information is available concerning the long-term settlement behaviour of drilled pier foundations socketed into rock. This paper summarizes the results of laboratory investigations of the long-term settlement (creep) behaviour of model socketed pier foundations. The testing program included seven model piers constructed with different materials and different load-support conditions. The primary models were two small-diameter concrete piers constructed in soft shale. For all models tested the results indicated similarly shaped time–displacement curves, having two distinct regions. The initial portion of the curves represents a region of primary creep and the remaining portion represents a zone of secondary creep having a much lower rate of displacement. A comparison of short-term (1 day, which is a normal maximum duration of a full-scale load test) and long-term (200 days) settlements for the model piers showed an 84–245% increase in settlements. In addition, some information concerning load transfer with time in the model piers and available data from loading tests on large-scale socketed piers are included. Key words: socketed pier foundations, long-term settlement, creep model tests, soft rock.
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Li, Lei, Yan Xiao und Rui Zhen Yang. „Experimental Study on Creep and Mechanical Behavior of Modern Bamboo Bridge Structure“. Key Engineering Materials 517 (Juni 2012): 141–49. http://dx.doi.org/10.4028/www.scientific.net/kem.517.141.
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A full-scale testing model of laminated bamboo truck load bridge was made based on the original structure. The mid-span deflection of CFRP-reinforced bamboo girders, temperature and relative air humidity were obtained through over three years creep test under self-weight, and the analysis based on experimental results was finished. The results indicate that the average creep deflection of the girders after three years is approximately 8-mm. In addition, the increase in temperature and humidity may contribute to creep. On the basis of creep test, a short-term loading test was carried out applied with dead load, and the bridge collapsed under the load of 18.5-t. By the analysis of the experimental results, it is realized that long span CFRP-reinforced bamboo girders have sufficient capacity to meet the strength and durability needs of practical use. Although CFRP layers could improve the performance of bamboo girders effectively, there is a decrease in strength and stiffness when considering the long-term performance. All these studies may contribute to improving the design of bamboo bridge structures, and some construction measures are suggested for the bamboo bridge according to the results of the experimental and analysis results.
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Hyde, T. H., und W. Sun. „A novel, high-sensitivity, small specimen creep test“. Journal of Strain Analysis for Engineering Design 44, Nr. 3 (20.02.2009): 171–85. http://dx.doi.org/10.1243/03093247jsa502.
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This paper describes a novel, high-sensitivity, ring-type of small specimen creep test method, which can be used to obtain accurate creep strain data. A full theoretical description of the test technique is given; this is based on the complementary strain energy approach, which leads to an analytical solution for the load line deformation of an elliptical ring. Using the analytical solution, a reference stress approach is used to establish the conversion relationships between the applied load and the equivalent uniaxial stress and between the experimentally measured creep deformations and the equivalent uniaxial creep strains. The main features of the test method are: (a) the ring specimen has a significantly larger equivalent gauge length (EGL), when compared with that of other small specimen types; (b) the method is suitable for testing at lower stresses compared with commonly used current small-specimen test methods (this is because relatively low strains can be obtained from relatively large deformations); (c) specimens have simple geometries and the tests are easy to perform, and (d) the conversion relationships are material independent and practically insensitive to geometry change due to deformation. Experimental validation of the test method is made using the results obtained from creep tests for a P91 steel at 650 °C. Practical applications and future exploitation of the technique are addressed.
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Clark, J. I., S. McKeown und C. B. Crawford. „Field measurements of the behavior of inclined footings on a natural slope“. Canadian Geotechnical Journal 25, Nr. 4 (01.11.1988): 662–74. http://dx.doi.org/10.1139/t88-077.
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Full-scale field testing for the bearing capacity and stability of inclined footings with anchors was carried out on a colluvial slope near the east portal of the Rogers Pass tunnel in British Columbia. The 35° natural slope was composed of granular material with an angle of shearing resistance [Formula: see text]. A series of small footings (area 1.14 m2) was loaded with anchor loads only and one large footing (area 2.66 m2) was loaded with both anchor and vertical loads up to 2100 kN. Bearing capacity coefficients were back calculated and compared with coefficients from bearing capacity theories. Elastic and deformation moduli were calculated from load–displacement curves during loading and unloading and creep rates were observed at intervals during the tests. Key words: inclined footings, instrumentation, bearing capacity factors, soil anchors, natural slopes, colluvial soils, soil creep, deformation modulus, elastic modulus.
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Deblieck, Rudy, Britta Gerets, Mark Boerakker, Harm Caelers, Arno Wilbers und Tine Boonen. „Relation between life time, failure stress and craze microstructure in polyethylene as evidenced by fracture surface texture analysis after an accelerated Full-Notch Creep Test“. Polymer 176 (August 2019): 264–73. http://dx.doi.org/10.1016/j.polymer.2019.04.033.
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Xu, Wenjin, Maodan Yuan, Weiming Xuan, Xuanrong Ji und Yan Chen. „Quantitative Inspection of Complex-Shaped Parts Based on Ice-Coupled Ultrasonic Full Waveform Inversion Technology“. Applied Sciences 11, Nr. 10 (13.05.2021): 4433. http://dx.doi.org/10.3390/app11104433.
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Ultrasonic methods have been extensively developed in nondestructive testing for various materials and components. However, accurately extracting quantitative information about defects still remains challenging, especially for complex structures. Although the immersion technique is commonly used for complex-shaped parts, the large mismatch of acoustic impedance between water and metal prevents effective ultrasonic transmission and leads to a low signal-to-noise ratio(SNR). In this paper, a quantitative imaging method is proposed for complex-shaped parts based on an ice-coupled full waveform inversion (FWI) method. Numerical experiments were carried out to quantitatively inspect the various defects in a turbine blade. Firstly, the k-space pseudospectral method was applied to simulate ice-coupled ultrasonic testing for the turbine blade. The recorded full wavefields were then applied for a frequency-domain FWI based on the Limited-memory Broyden–Fletcher–Goldfarb–Shanno (L-BFGS) method. With a carefully selected iterative number and frequency, a successive-frequency FWI can well detect half wavelength defects. Extended studies on an open notch with different orientations and multiple adjacent defects proved its capability to detect different types of defects. Finally, an uncertainty analysis was conducted with inaccurate initial velocity models with a relative error of ±2%, demonstrating its robustness even with a certain inaccuracy. This study demonstrates that the proposed method has a high potential to inspect complex-shaped structures with an excellent resolution.
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van Leeuwen, Hans, Don van Delft, John Heijdra, Henk Braam, Eric R. Jørgensen, Denja Lekou und Pantelis Vionis. „Comparing Fatigue Strength From Full Scale Blade Tests With Coupon-Based Predictions“. Journal of Solar Energy Engineering 124, Nr. 4 (01.11.2002): 404–11. http://dx.doi.org/10.1115/1.1509463.
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In order to get a deeper understanding of the blade-to-blade variations and to determine the statistical distribution of the fatigue strength of rotor blades, 37 small rotor blades have been tested in static and fatigue loading. The blades are 3.4 m commercially available blades adapted to the needs of the project. In addition to these blade tests, coupons of the blade material have been tested. The tests have encompassed static flapwise bending tests, flapwise fatigue tests at two different sections of the blade, and edgewise fatigue tests. Since some blades could be re-used after a first test, a total number of 42 blade tests has been carried out in three different testing laboratories. The blades showed large deformation, development of creep and stiffness reduction. After correction for these phenomena, the fatigue strength of the blades was predicted very well by the classical Goodman relation using the well-known slope parameter of 10.
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Golikov, N. I., M. M. Sidorov, I. I. Sannikov und A. K. Rodionov. „Study of the mechanical properties of the gas pipeline metal after long-term operation in conditions of the North“. Industrial laboratory. Diagnostics of materials 86, Nr. 6 (22.06.2020): 48–54. http://dx.doi.org/10.26896/1028-6861-2020-86-6-48-54.
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The residual strength and technical condition of the material of 530-mm steel pipe (14KhGS) of main gas pipeline are estimated to ensure the safety of long-term operation of pipelines in climatic conditions of the North. The mechanical properties are determined using standard methods of mechanical testing in laboratory conditions. A full-scale pressure test up to failure is used to determine the actual values of the fracture toughness and safety factor of the pipe. Full-scale tests were carried out on a test bench, a computer-measuring complex which displayed the reaction of the object to the load. A pipe fragment was cut from the linear part of the main gas pipeline and welded with spherical plugs. The outer surface of the pipe was notched along the pipe axis. The depth of the notch was calculated such that the breaking load on the ligament section at the notch site corresponded to the working pressure of the gas pipeline. No significant changes in the mechanical properties of the pipe metal were revealed in the absence of visible corrosion and deformation damage during long-term operation of the pipe in the North. Impact tests did not reveal embrittlement of the metal of the tested pipes. Full-scale tests of a pipe with an artificially applied defect made it possible to calculate the value of the critical stress intensity factor, which allowed us to estimate the residual strength of a pipe with a longitudinal crack. The value of the strength criterion of the fracture mechanics indicates the preservation of a sufficiently high viscosity of sheet metal pipes. Similar tests of the pipes (of other size and made of other materials) operating in the main gas pipelines should be continued taking into account temperature ranges and material degradation after long-term operation.
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Whittenberger, J. Daniel, Eduard Arzt und Michael J. Luton. „Preliminary investigation of a NiAl composite prepared by cryomilling“. Journal of Materials Research 5, Nr. 2 (Februar 1990): 271–77. http://dx.doi.org/10.1557/jmr.1990.0271.
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An attempt has been made to improve the high temperature mechanical strength of the B2 cubic crystal structure intermetallic NiAl by dispersion strengthening. Prealloyed Ni–51 (at.%) Al was cryomilled with a Y2O3 addition to form an yttria dispersoid within the intermetallic matrix. Following milling, the powder was hot extruded to full density and machined into test coupons. Compression testing between 1200 and 1400 K indicated that the cryogenic process yielded the strongest NiAl based material tested to date: creep resistance was six times better than NiAl and twice that of a NiAl particulate composite containing 10 vol.% TiB2. Surprisingly, transmission electron microscopy revealed that the second phase was inhomogeneously distributed. Furthermore, x-ray analysis indicated that the second phase was not Y2O3 but rather AIN.
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Miyamoto, Byrne, Nathan J. Bechle, Douglas R. Rammer und Samuel L. Zelinka. „A Small-Scale Test to Examine Heat Delamination in Cross Laminated Timber (CLT)“. Forests 12, Nr. 2 (17.02.2021): 232. http://dx.doi.org/10.3390/f12020232.
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This paper examines the strength of wood adhesive bonds at high temperatures. The goal of this research is to better understand the conditions of heat delamination in cross laminated timber (CLT) that is exposed to fire. Heat delamination in CLT occurs when one lamination detaches from the composite panel before the char front reaches the bondline. Timber that falls from the panel, as a result of delamination, contributes additional fuel to the fire, which can cause fire regrowth, while the loss of a lamination causes a sudden loss in strength. Currently, to demonstrate that an adhesive does not delaminate, it must pass a full scale (6 m by 3 m) compartment fire test as prescribed in the PRG-320 product standard. In this work, we scaled down the mechanical loads and temperatures to 300 mm lap shear specimens. Seven different adhesives were tested and compared against solid wood controls with the same geometry as the lap shear specimens. Quasi-static tests were run where the specimens were loaded to failure at 25 °C and 260 °C, when the samples were at thermal equilibrium. Additionally, creep tests were performed where the load and temperature ramp was matched to the adhesive bondline temperatures measured in the large scale PRG-320 tests. With the exception of some of the polyurethane formulations, all adhesives passed the scaled-down creep test that resembles the PRG-320 standard. Of the polyurethane adhesives tested, only one formulation remained intact for the duration of the test. These results can be used to help better predict which adhesives may pass the PRG-320 test prior to full scale testing.
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Kasl, Josef, und Dagmar Jandová. „Metallography of CB2 Steel Used for Cast Turbine Components“. Materials Science Forum 782 (April 2014): 179–85. http://dx.doi.org/10.4028/www.scientific.net/msf.782.179.
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Steel CB2 developed in frame of the COST actions belongs to the most promising steel for production of cast turbine components working at ultra-supercritical steam conditions. VZÚ Plzeň has participated on assessment of original trial melt CB2 as well as on testing of samples coming from one of pilot valves produced of steel CB2 in full scale. Recently VZÚ Plzeň has cooperated with Doosan Škoda Power in development of weld processes of advanced power energy steels including steel CB2. This contribution deals with a comparison of properties of the steel CB2 produced by four various steelmakers from point of view of their microstructure in relation with their mechanical and creep resistant properties. Evaluation is focused on chemical heterogeneity, porosity, content of non-metallic inclusions, in particular on an occurrence of coarse NB, microstructure and substructure using methods of light and electron microscopy.
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Safina, Larisa, Aleksandr Shuvalov und Mikhail Kovalev. „Study of reinforced elastomeric bearings for structures in seismic areas“. MATEC Web of Conferences 193 (2018): 03009. http://dx.doi.org/10.1051/matecconf/201819303009.
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The article presents the results of the experimental determination of the physical and mechanical characteristics of rubber-metal vibration-proof supports used in the construction of facilities in the areas of increased seismic hazard. The testing was based on two necessities: to substantiate the possibility of using such a constructive seismic protection solution and to create reliable calculation models of the structures with rubber-metal support. More than thirty samples were tested in the laboratory under various loads and impacts. The elastomers were tested in accordance with the requirements written in EN-1337-3. The experiment was performed on three types of elastomer model samples to determine their vertical and horizontal stiffness, the tensile strength and modulus of elasticity and creep. The work was performed on INSTRON power equipment and a test rig equipped with MTS hydraulic jacks installed in the power frame. The testing results of elastomeric support models were confirmed by the determination of individual characteristics on the full size specimens at the corresponding load. Thus, the test has confirmed and proved the validity of the use of elastomeric bearings for seismic protection of a mall construction.
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Davies, C. M., N. P. O'Dowd, K. M. Nikbin, G. A. Webster und F. Biglari. „Comparison of methods for obtaining crack-tip stress distributions in an elastic-plastic material“. Journal of Strain Analysis for Engineering Design 40, Nr. 5 (01.07.2005): 431–49. http://dx.doi.org/10.1243/030932405x16098.
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Under linear elastic and elastic-plastic conditions the K field and the HRR (Hutchinson-Rice-Rosengren) field respectively are expected to provide an accurate representation of the stress field close to the crack tip in an elastic-plastic material. It has recently been proposed in French and UK defect assessment procedures that the Neuber method, originally developed for sharply curved notches, provides an alternative approach to estimate both notch and crack-tip stress fields, for use in conjunction with the sigma- d (σd) method to predict creep crack initiation times. In this work, the crack-tip stress fields under plane strain conditions, predicted from the Neuber approach, are compared with the HRR and K fields as well as those obtained from full-field finite element calculations. A compact tension and a single edge notched tension specimen have been examined; the material model used is the Ramberg-Osgood, power law plasticity model. As expected, the K field and HRR field have been found to provide a good representation of the near-tip fields at low and high loads respectively. Satisfactory solutions have also been obtained through the use of the reference stress to estimate the amplitude of the crack-tip stress in conjunction with the HRR field. The Neuber approach provides a good estimate of the equivalent (von Mises) stresses over the full range of load levels. However, but the use of the Neuber approach directly to predict the maximum principal stress in the plane of the crack provides a non-conservative prediction. A modified Neuber method, using an appropriate scaling function, has been proposed to determine the maximum principal stress in the plane of the crack from the equivalent (von Mises) stress predicted by the Neuber approach. Using the proposed method, a significantly improved estimate of the crack-tip stresses is obtained.
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Markosian, Nick, Raed Tawadrous, Mohammad Mastali, Robert J. Thomas und Marc Maguire. „Performance Evaluation of a Prestressed Belitic Calcium Sulfoaluminate Cement (BCSA) Concrete Bridge Girder“. Sustainability 13, Nr. 14 (14.07.2021): 7875. http://dx.doi.org/10.3390/su13147875.
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Belitic calcium sulfoaluminate (BCSA) cement is a sustainable alternative to Portland cement that offers rapid setting characteristics that could accelerate throughput in precast concrete operations. BCSA cements have lower carbon footprint, embodied energy, and natural resource consumption than Portland cement. However, these benefits are not often utilized in structural members due to lack of specifications and perceived logistical challenges. This paper evaluates the performance of a full-scale precast, prestressed voided deck slab bridge girder made with BCSA cement concrete. The rapid-set properties of BCSA cement allowed the initial concrete compressive strength to reach the required 4300 psi release strength at 6.5 h after casting. Prestress losses were monitored long-term using vibrating wire strain gages cast into the concrete at the level of the prestressing strands and the data were compared to the American Association of State Highway and Transportation Officials Load and Resistance Factor Design (AASHTO LRFD) predicted prestress losses. AASHTO methods for prestress loss calculation were overestimated compared to the vibrating wire strain gage data. Material testing was performed to quantify material properties including compressive strength, tensile strength, static and dynamic elastic modulus, creep, and drying and autogenous shrinkage. The material testing results were compared to AASHTO predictions for creep and shrinkage losses. The bridge girder was tested at mid-span and at a distance of 1.25 times the depth of the beam (1.25d) from the face of the support until failure. Mid-span testing consisted of a crack reopening test to solve for the effective prestress in the girder and a flexural test until failure. The crack reopen effective prestress was compared to the AASHTO prediction and AASHTO appeared to be effective in predicting losses based on the crack reopen data. The mid-span failure was a shear failure, well predicted by AASHTO LRFD. The 1.25d test resulted in a bond failure, but nearly developed based on a moment curvature estimate indicating the AASHTO bond model was conservative.
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Chao, Ching-Kong, You-Lin Chen und Jinn Lin. „Half-threaded holes markedly increase the fatigue life of locking plates without compromising screw stability“. Bone & Joint Research 9, Nr. 10 (01.10.2020): 645–52. http://dx.doi.org/10.1302/2046-3758.910.bjr-2019-0237.r2.
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Aims To determine whether half-threaded screw holes in a new titanium locking plate design can substantially decrease the notch effects of the threads and increase the plate fatigue life. Methods Three types (I to III) of titanium locking plates were fabricated to simulate plates used in the femur, tibia, and forearm. Two copies of each were fabricated using full- and half-threaded screw holes (called A and B, respectively). The mechanical strengths of the plates were evaluated according to the American Society for Testing and Materials (ASTM) F382-14, and the screw stability was assessed by measuring the screw removal torque and bending strength. Results The B plates had fatigue lives 11- to 16-times higher than those of the A plates. Before cyclic loading, the screw removal torques were all higher than the insertion torques. However, after cyclic loading, the removal torques were similar to or slightly lower than the insertion torques (0% to 17.3%), although those of the B plates were higher than those of the A plates for all except the type III plates (101%, 109.8%, and 93.8% for types I, II, and III, respectively). The bending strengths of the screws were not significantly different between the A and B plates for any of the types. Conclusion Removing half of the threads from the screw holes markedly increased the fatigue life of the locking plates while preserving the tightness of the screw heads and the bending strength of the locking screws. However, future work is necessary to determine the relationship between the notch sensitivity properties and titanium plate design. Cite this article: Bone Joint Res 2020;9(10):645–652.