Journal articles: 'Compression twin'

1

Adams, G. P., and W. Soedel. "Computation of Compression Loads in Twin Screw Compressors." Journal of Mechanical Design 117, no. 4 (December 1, 1995): 512–19. http://dx.doi.org/10.1115/1.2826712.

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The compression mechanism in a twin screw compressor consists of two helical rotors. In this work, a method is presented for computing the forces and moments induced on each rotor due to gas compression. These are defined as the compression loads. The helical rotor surfaces are defined by the end profiles, wrap angle and rotor length. The 3D surface of each rotor is mapped to 2D integration regions. These regions correspond to the surfaces associated with individual compression chambers. The compression loads are computed by integrating the chamber pressure over the rotor surfaces. The integrals are evaluated at incremental values of the rotor angular position. The method is presented and implemented for a specific compressor configuration. The compression loads are resolved to forces at the bearing locations. These bearing forces are presented for operating pressures which represent an under-pressure condition. A frequency analysis demonstrates the rich frequency content of the bearing forces due to the sharpness of the compression loads as a function of the rotor angular position. In addition, it is demonstrated that the moment load about the axis of rotation induced on the female is approximately 12 percent of that induced on the male. Therefore, the female rotor motion approaches that of an idler gear.

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2

Lee, B. H., S. H. Park, Mohamad El Mehtedi, E. Evangelista, and Chong Soo Lee. "Influence of Initial Texture on Twin Formation and Plastic Deformation of Rolled AZ31 Mg Alloy." Advanced Materials Research 26-28 (October 2007): 149–52. http://dx.doi.org/10.4028/www.scientific.net/amr.26-28.149.

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The influence of initial texture on the formation of primary twin system of AZ31 Magnesium rolled plate was investigated in this work. Uniaxial compression tests were carried out on samples cut along the rolling direction (RD) and normal direction (ND) of rolled AZ31 Mg plate at various temperatures (RT, 150, 200, 250, 300, 350, 400, 450°C) with the fixed strain rate (0.01s-1). The results showed that the primary twinning system of AZ31 Mg alloy (c-axis extension twin) occurred actively in the RD compression specimens, which promoted homogeneous deformation as compared to the ND compression specimens. The effect of temperature on the formation of deformation twins was also investigated, and slip/twin transition temperature was found to be 250°C.

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3

Hou, Long, Ying Niu, Yanchao Dai, Lansong Ba, Yves Fautrelle, Zongbin Li, Bo Yang, Claude Esling, and Xi Li. "Stress-induced detwinning and martensite transformation in an austenite Ni–Mn–Ga alloy with martensite cluster under uniaxial loading." IUCrJ 6, no. 3 (March 27, 2019): 366–72. http://dx.doi.org/10.1107/s2052252519003208.

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Stress-induced martensitic detwinning and martensitic transformation during step-wise compression in an austenite Ni–Mn–Ga matrix with a martensite cluster under uniaxial loading have been investigated by electron backscatter diffraction, focusing on the crystallographic features of microstructure evolution. The results indicate that detwinning occurs on twins with a high Schmid factor for both intra-plate and inter-plate twins in the hierarchical structure, resulting in a nonmodulated (NM) martensite composed only of favourable variants with [001]NM orientation away from the compression axis. Moreover, the stress-induced martensitic transformation occurs at higher stress levels, undergoing a three-stage transformation from austenite to a twin variant pair and finally to a single variant with increasing compressive stress, and theoretical calculation shows that the corresponding crystallographic configuration is accommodated to the compression stress. The present research not only provides a comprehensive understanding of martensitic variant detwinning and martensitic transformation under compression stress, but also offers important guidelines for the mechanical training process of martensite.

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4

Ando, Shinji, Masayuki Tsushida, and Hiromoto Kitahara. "Deformation Behavior of Magnesium Single Crystal in c-Axis Compression and a-Axis Tension." Materials Science Forum 654-656 (June 2010): 699–702. http://dx.doi.org/10.4028/www.scientific.net/msf.654-656.699.

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In general, deformation behavior of magnesium in compression is different from tensile. To investigate deformation behavior of magnesium single crystals by non-basal slips and twins, c-axis compression and a-axis tension tests were performed in the range of 77K-573K. The crystals were yielded by second order pyramidal slip, and the yield stress shows anomalous temperature dependence (increased with increasing temperature) between 203K and 293K. Yield stress of c-axis compression was bigger than that of a-axis tensile. In compression, fracture surface were (11 4) under 293K and were {30 4} above 373K, and fracture strain was smaller than the case of tension test. {10 1}-{10 2} double twin were activated at higher temperature and the crystal, therefore, fractured along the twin interface.

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5

Bao, Lei, Yudong Zhang, Christophe Schuman, Jean-Sébastien Lecomte, Marie-Jeanne Philippe, Xiang Zhao, and Claude Esling. "Multiple twinning in pure hexagonal close-packed titanium." Journal of Applied Crystallography 46, no. 5 (September 18, 2013): 1397–406. http://dx.doi.org/10.1107/s002188981302253x.

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Commercial pure titanium (T40) was deformed in channel die compression by means of the split-sample technique in order to study multiple twinning. Particular attention was paid to the twin variant presentation and selection during multiple twinning. All possible misorientations, corresponding to the multiple twins arising from the combination of the {1 1 {\overline 2} 2} compression (C) twin, the {1 0 {\overline 1} 2} tension twin (T1) and the {1 1 {\overline 2} 1} tension twin (T2), were calculated with respect to the crystal basis of the matrix grain. All the multiple twin variants are partitioned into ten classes with the same crystallographically equivalent misorientation angle and axis. However, when the influence of twinning order is taken into account, the multiple twin variants are partitioned into 15 classes. Experimental results prove that the selection of twin variants (primary and secondary) is mainly governed by their macroscopic Schmid factor (SF). The normalized SF is more efficient at predicting variant selection. A twin formed in one grain can activate another twin in a neighbouring grain, provided that the angle between the two twinning planes does not exceed 20°.

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6

Ferreira, C. A. Infante, C. Zamfirescu, and D. Zaytsev. "Twin screw oil-free wet compressor for compression–absorption cycle." International Journal of Refrigeration 29, no. 4 (June 2006): 556–65. http://dx.doi.org/10.1016/j.ijrefrig.2005.10.006.

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7

Li, Xiao, Ping Yang, and Li Meng. "Orientational Analysis on Static Recrystallization at Tension Twins in AZ31 Magnesium Alloy." Advanced Materials Research 299-300 (July 2011): 778–84. http://dx.doi.org/10.4028/www.scientific.net/amr.299-300.778.

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The deformation depends on twinning in Mg alloy, and twins will be the dominant recrystallization nucleation site. Tension twinning proceeds much more easily than compression twinning since its volume fraction is much higher than that of compression twins, which may have a promotive effect on the recrystallization to a certain degree. Based on the previous research on the static recrystallization at compression twins, the evolution of microstructure and texture in AZ31 magnesium alloy during its static recystallization at tension twins was further investigated; and the orientational characteristics of new grains formed at tension twins in the early stage of static recrystallization were analyzed by EBSD technique. The results showed that the strong basal texture was retained and weakened with no new texture component being detected during annealing. New grains were observed to nucleate preferentially at the intersections of tension twin variants or the intersection between tension twins and compression twins. Their orientations are relatively random and are strongly scattered from those of original tension twins or compression twins. A comparison of the recrystallization at tension twins and compression twins was further made.

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8

Hu, Wei Hui, Tian Mo Liu, and Qing Liu. "Research on Hot Upsetting Deformation Behavior and Dynamic Recrystallization for AZ31." Key Engineering Materials 353-358 (September 2007): 722–25. http://dx.doi.org/10.4028/www.scientific.net/kem.353-358.722.

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The AZ31 Mg alloy was upseted from 250°C to 500°C. In optical microscopy, as the temperature increases, the volume fraction of deformation twin will reduce to a minium and vanish. Simultaneously, some small dynamically recrystallized grains were observed at the boundaries of origin grains and twins. When temperatures rise from 350°C to 500°C , the volume fraction and size of DRX grains increases .By the compression test of the upsetting proof samples, the compressive strength reach a maxium, and reduce during further rising temperatures.

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9

Parlangeau, Camille, Alexandre Dimanov, Olivier Lacombe, Simon Hallais, and Jean-Marc Daniel. "Uniaxial compression of calcite single crystals at room temperature: insights into twinning activation and development." Solid Earth 10, no. 1 (February 7, 2019): 307–16. http://dx.doi.org/10.5194/se-10-307-2019.

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Abstract. E-twinning is a common plastic deformation mechanism in calcite deformed at low temperature. Strain rate, temperature and confining pressure have negligible effects on twinning activation which is mainly dependent on differential stress. The critical resolved shear stress (CRSS) required for twinning activation is dependent on grain size and strain hardening. This CRSS value may obey the Hall–Petch relation, but due to sparse experimental data its actual evolution with grain size and strain still remains a matter of debate. In order to provide additional constraints on twinning activation and development, new mechanical tests were carried out at room temperature on unconfined single crystals of calcite, with different sizes and crystallographic orientations. Uniaxial deformation was performed at a controlled displacement rate, while the sample surface was monitored using optical microscopy and a high-resolution CCD (charge-coupled device) camera. The retrieved macroscopic stress–strain behavior of the crystals was correlated with the surface observations of the deformation process. Results show (1) the onset of crystal plasticity with the activation of the first isolated mechanical twins during the strain hardening stage, and (2) the densification and thickening of twin lamellae during the steady-state flow stress stage. Such thickening of twin lamellae at room temperature emphasizes that calcite twin morphology is not controlled solely by temperature. The different values for the CRSS obtained for the activation of isolated twins and for the onset of twin densification and thickening raises questions regarding the appropriate value to be considered when using calcite twin data for stress inversion purposes.

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10

Sun, Jing Li, and Jing Tao Wang. "Microstructures and Mechanical Properties of Pure Titanium by Dynamic Plastic Deformation." Materials Science Forum 667-669 (December 2010): 337–42. http://dx.doi.org/10.4028/www.scientific.net/msf.667-669.337.

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Dynamic plastic deformation of commercially pure titanium in the temperature range of -100-18°C at the strain rates of 3.0×102-2.5×103, as well as at quasi-static compression were carried out by a Split Hopkinson Pressure Bar technique and conventional compression testing machine respectively. The formation of deformation twins plays a key role on the accommodation of a large amount of strain produced by plastic deformation. Grain orientation has a great influence on the formation of twins. Temperature has smaller effects than strain rate on the evolutions of the microstructures and mechanical properties. The area fraction of twins and their intersections increase with the increasing strain rate and the deformation strain, resulting in refined microstructures and higher hardness values. Strain rate also leads to the change of twin shape (type). While more lenticular twins are observed in samples after quasi-static deformation, there are lots of needle-like twins with straight and long boundaries in samples processed via dynamic plastic deformation. This may imply that different twin systems operate at different strain rate. For the needle-like twins in samples after dynamic plastic deformation, the twin area fraction approaches saturation beyond the true strain of about 0.13, which is significant turning point for twinning rate. This saturated trend is not observed in quasi-static deformation.

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11

Sułkowski, Bartosz. "The effect of structure and texture on pure magnesium properties." International Journal of Materials Research 112, no. 1 (January 1, 2021): 57–62. http://dx.doi.org/10.1515/ijmr-2020-7815.

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Abstract Deformation modes and twin hardening of pure magnesium under compression in respect of the initial structure and texture were studied in the present work. In general, samples had two types of texture with different alignment of c-axis in respect to a compression direction. In the first case, most of the grains have the c-axis parallel to the compression direction and in the second case, the c-axis was perpendicular with the compression direction. It was found that coarse grained material deformed by slip despite the type of the texture, while the fine grained samples, with c-axis perpendicular to the compression direction, deformed by twinning. The samples which deform by twinning exhibited the highest yield point. It was concluded that combination of the fine grained structure and hard type texture components may introduce twinning as the main deformation mode and may increase the mechanical properties of magnesium and its alloys. The model for twin induced hardening is proposed where twins act as the grain refinement factor.

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12

Tolnai, Domonkos, Marie-Anne Dupont, Serge Gavras, Klaudia Fekete-Horváth, Andreas Stark, Norbert Schell, and Kristián Máthis. "In Situ Synchrotron Diffraction Analysis of Zn Additions on the Compression Properties of NK30." Materials 12, no. 23 (November 28, 2019): 3935. http://dx.doi.org/10.3390/ma12233935.

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In situ synchrotron radiation diffraction was performed during the compression of as-cast Mg–3Nd–Zn alloys with different amounts (0, 0.5, 1, and 2 wt %) of Zn addition at room temperature. During the tests, the acoustic emission signals of the samples were recorded. The results show that the addition of Zn decreased the strength of the alloys but, at the same time, increased their ductility. In the earlier stages of deformation, twin formation and basal slip were the dominant deformation mechanisms. The twins tended to grow during the entire compression stage; however, the formation of new twins dominated only at the beginning of the plastic deformation. In order to accommodate the strain levels, the alloys containing Zn underwent nonbasal slip in the later stages of deformation. This can be attributed to the presence of precipitates containing Zn in the microstructure, inhibiting twin growth.

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13

Chen, Fulong, Kaidi Li, Bin Tang, Degui Liu, Hong Zhong, and Jinshan Li. "Deformation Behavior and Microstructural Evolution of Inconel 625 Superalloy during the Hot Compression Process." Metals 11, no. 5 (May 18, 2021): 824. http://dx.doi.org/10.3390/met11050824.

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Hot deformation behavior and the microstructural evolution of Inconel 625 superalloy plates are investigated by hot compression tests in a range of working temperatures (800–1050 °C) and strain rates (0.001–1 s−1). The microstructural observation shows that a strong <110> texture forms when the processing temperature is below 950 °C, whose intensity decreases with the increases of the temperature, and it disappears when compressing above 950 °C. During the compression test, twin-related dynamic recrystallization (DRX) occurs in the investigated temperature range, and the intensity of twin-related DRX increases with the increases of the temperature. In addition, as the temperature increases, the intensity of continuum DRX decreases.

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14

Guo, Zherui, Weinong Chen, and James Zheng. "Improved quasi-static twin-fiber transverse compression of several high-performance fibers." Textile Research Journal 89, no. 9 (May 11, 2018): 1595–613. http://dx.doi.org/10.1177/0040517518775927.

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The method of determining the quasi-static transverse compressive response of several high-performance polymer fibers was improved upon from a previous twin-fiber transverse compression setup in order to detect small initial high compliance signals while maintaining consistent diametral compression. Two fibers were laid parallel between two polished tool steel platens, and the fibers were subsequently compressed using a piezo-electric actuator at quasi-static rates. The new experimental setup ensures that the compression cycle begins when extremely small load signals are detected so that initial elastic transverse moduli may be more accurately measured. Nominal stress–strain curves were obtained for several types of high-performance fibers. The results show good agreement with previously obtained measurements. S-glass fibers exhibited a vastly different mechanical response compared to the polymer fibers.

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15

Fitzner, Arnas, D. G. Leo Prakash, Joao Quinta da Fonseca, Michael Preuss, Matthew J. Thomas, Shu Yan Zhang, and Joe Kelleher. "The Effect of Aluminium on Deformation and Twinning in Alpha Titanium: The 45° Case." Materials Science Forum 765 (July 2013): 549–53. http://dx.doi.org/10.4028/www.scientific.net/msf.765.549.

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The deformation behaviour of binary Ti-Al model alloys has been observed in respect to nucleation, propagation and growth of twins, specifically the interaction of slip and {1 0 -1 2} tensile twins. The area fraction of twins increases by trend from Ti-0Al to Ti-4Al but significantly reduces to Ti-6Al. The lattice strain evolution during compression was measured using in-situ neutron diffraction and decreases from Ti-0Al to Ti-4Al but increases to Ti-6Al. The twin activity in hcp Ti behaves as expected from fcc materials until 4 wt.% Al concentration, but it is believed that short or long range ordering reduces the twin activity in Ti-6Al.

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16

Song, Lin, Xiang Jun Xu, Jun Pin Lin, and Lai Qi Zhang. "The Microstructure and Compression Behavior of Multi-Step Forging Ti-45Al-8Nb Alloy after Annealing at 1100 °C." Materials Science Forum 747-748 (February 2013): 111–14. http://dx.doi.org/10.4028/www.scientific.net/msf.747-748.111.

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Effects of annealing treatment on microstructure and the compressive properties of hot-worked Ti-45Al-8Nb-(W, B, Y) alloy were investigated. Microstructure of the extrusion plus multi-step forging pancake before and after heat treatment was analyzed by SEM and TEM, respectively. The annealing was conducted by holding samples at 1100°C for 2hrs, and followed by air cooling and furnace cooling. The mechanical properties were measured by Instron test machine. The microstructure evolution during compressive deformation was analyzed by TEM. The results showed that after the annealing the microstructure change could not be observed under SEM but can be observed under TEM. Many dislocation clusters were removed by heat treatment. The heat treated samples had similar compression behaviors with the pancake. TEM investigation showed that the numerous twin intersections occured in γ matrix during compression. The twin spaces tended to decrease as the deformation and the intersection increasing.

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17

Hidalgo-Manrique, Paloma, and Joseph D. Robson. "Influence of Precipitation on Twinning in a Mg-Al-Zn Alloy." Materials Science Forum 941 (December 2018): 1041–46. http://dx.doi.org/10.4028/www.scientific.net/msf.941.1041.

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A textured Mg-Al-Zn alloy rolled plate was solution treated and aged at 320 oC for 2 h and 116 h, respectively. Afterwards, the three conditions were compressed at room temperature along the transverse direction to activate {110} twinning. Ageing treatments were observed to strengthen the alloy in relation to the solution-treated condition. This has been mainly attributed to the restricted lateral growth of twins in the presence of particles and thus to the additional stress required for twin growth. Accordingly, a slightly reduced twin volume fraction, but an increased number of smaller twins was observed after compression in the aged samples.

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18

Yang, Xiaoyue, Shuang Xu, and Qingjia Chi. "Plastic Deformation Behavior of Bi-Crystal Magnesium Nanopillars with a { 10 1 ¯ 2 } Twin Boundary under Compression: Molecular Dynamics Simulations." Materials 12, no. 5 (March 5, 2019): 750. http://dx.doi.org/10.3390/ma12050750.

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In this study, molecular dynamics simulations were performed to study the uniaxial compression deformation of bi-crystal magnesium nanopillars with a { 10 1 ¯ 2 } twin boundary (TB). The generation and evolution process of internal defects of magnesium nanopillars were analyzed in detail. Simulation results showed that the initial deformation mechanism was mainly caused by the migration of the twin boundary, and the transformation of TB into (basal/prismatic) B/P interface was observed. After that, basal slip as well as pyramidal slip nucleated during the plastic deformation process. Moreover, a competition mechanism between twin boundary migration and basal slip was found. Basal slip can inhibit the migration of the twin boundary, and { 10 1 ¯ 1 } ⟨ 10 1 ¯ 2 ⟩ twins appear at a certain high strain level ( ε = 0.104). In addition, Schmid factor (SF) analysis was conducted to understand the activations of deformation modes.

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19

Russell, William D., Nicholas R. Bratton, YubRaj Paudel, Robert D. Moser, Zackery B. McClelland, Christopher D. Barrett, Andrew L. Oppedal, et al. "In Situ Characterization of the Effect of Twin-Microstructure Interactions on {1 0 1 2} Tension and {1 0 1 1} Contraction Twin Nucleation, Growth and Damage in Magnesium." Metals 10, no. 11 (October 22, 2020): 1403. http://dx.doi.org/10.3390/met10111403.

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Through in situ electron backscatter diffraction (EBSD) experiments, this paper uncovers dominant damage mechanisms in traditional magnesium alloys exhibiting deformation twinning. The findings emphasize the level of deleterious strain incompatibility induced by twin interaction with other deformation modes and microstructural defects. A double fiber obtained by plane-strain extrusion as a starting texture of AM30 magnesium alloy offered the opportunity to track deformation by EBSD in neighboring grains where some undergo profuse {1 0 1 2} twinning and others do not. For a tensile loading applied along extrusion transverse (ET) direction, those experiencing profuse twinning reveal a major effect of grain boundaries on non-Schmid behavior affecting twin variant selection and growth. Similarly, a neighboring grain, with its ⟨c⟩-axis oriented nearly perpendicular to tensile loading, showed an abnormally early nucleation of {1 0 1 1} contraction twins (2% strain) while the same {1 0 1 1} twin mode triggering under ⟨c⟩-axis uniaxial compression have higher value of critical resolved shear stress exceeding the values for pyramidal ⟨c + a⟩ dislocations. The difference in nucleation behavior of contraction vs. compression {1 0 1 1} twins is attributed to the hydrostatic stresses that promote the required atomic shuffles at the core of twinning disconnections.

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20

Shi, Dongfeng, Tianmo Liu, Dewen Hou, Huicong Chen, Fusheng Pan, and Hongbing Chen. "The effect of twin–twin interaction in Mg 3Al 1Zn alloy during compression." Journal of Alloys and Compounds 685 (November 2016): 428–35. http://dx.doi.org/10.1016/j.jallcom.2016.05.338.

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21

Basha, Nausheen, Ahmed Kovacevic, and Sham Rane. "Analysis of Oil-Injected Twin-Screw Compressor with Multiphase Flow Models." Designs 3, no. 4 (December 16, 2019): 54. http://dx.doi.org/10.3390/designs3040054.

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Growing demands for energy are motivating researchers to conduct in-depth analysis of positive displacement machines such as oil-injected screw compressors which are frequently used in industrial applications like refrigeration, oil and gas and air compression. The performance of these machines is strongly dependent on the oil injection. Optimisation of oil has a great energy saving potential by both increasing efficiency and reducing other impacts on the environment. Therefore, a three-dimensional, transient computational fluid dynamics study of oil injection in a twin-screw compressor is conducted in this research. This study explores pseudo single-fluid multiphase (SFM) models of VOF (Volume of Fluid) and a mixture for their capability to predict the performance of the oil-injected twin screw compressor and compare this with the experimental values. SCORGTM (Screw Compressor Rotor Grid Generator) is used to generate numerical grids for unstructured solver Fluent with the special interface developed to facilitate user defined nodal displacement (UDND). The performance predictions with both VOF and mixture models provide accurate values for power consumption and flow rates with low deviation between computational fluid dynamics (CFD) and the experiment at 6000 RPM and 7.0 bar discharge pressure. In addition, the study reflects on differences in predicting oil distribution with VOF, mixture and Eulerian-Eulerian two-fluid models. Overall, this study provides an insight into multiphase flow-modelling techniques available for oil-injected twin-screw compressors comprehensively accounting for the details of oil distribution in the compression chamber and integral compressor performance.

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22

Jiang, Jia, Andrew Godfrey, and Qing Liu. "EBSD Analysis and Theoretical Prediction of Twin Orientations during Compression in Mg-3Al-1Zn." Key Engineering Materials 353-358 (September 2007): 627–30. http://dx.doi.org/10.4028/www.scientific.net/kem.353-358.627.

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In order to improve the formability of magnesium alloys at low temperatures, a thorough understanding of the twinning behaviour is required. Cylindrical samples were compressed uniaxially from room temperature to 250oC, with the compression axis parallel to the transverse direction (TD) of a hot-rolled Mg-3Al-1Zn sheet. Twinning was investigated by use of orientation maps constructed from electron backscattered diffraction (EBSD) data. Tensile twinning was observed at all temperatures. In some grains two twin variants were observed. For each twin the specific twinning variant among the 6 possible twinning systems was identified by consideration of the twinning rotation. The twinning was then investigated by comparing the specific twin variant with the calculated Schmid factors for all 6 possible twin variants. In cases of grains that are completely reoriented by two twin variants it is possible to back-calculate the initial grain orientation by considering all possible twin rotations for both of the twin variants. It was found that the operative twin variants where those with the highest Schmid factors.

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23

Kitahara, Takaaki, Shinji Ando, Masayuki Tsushida, Hiromoto Kitahara, and Hideki Tonda. "Deformation Behavior of Magnesium Single Crystals in C-Axis Compression." Key Engineering Materials 345-346 (August 2007): 129–32. http://dx.doi.org/10.4028/www.scientific.net/kem.345-346.129.

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In general, deformation behavior of magnesium in compression is different from tensile. To investigate deformation behavior of magnesium single crystals, c-axis compression was performed. The crystals were yielded by second order pyramidal slip, and the yield stress shows anomalous temperature dependence (increased with increasing temperature) between 203K and 293K. Yield stress of c-axis compression is bigger than that of a-axis tensile. {10-13} twin and {11-24} twin occurred at 77293K and 77473K respectively. Fracture surface at 77293K was {11-24} and at 473K was {11-22}.

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24

Sato, Itsuya, Seiji Miura, and Tetsuo Mohri. "Twinning Behavior in AZ31-B Polycrystal Texture Subjected to In-Situ Bending Test." Materials Science Forum 654-656 (June 2010): 715–18. http://dx.doi.org/10.4028/www.scientific.net/msf.654-656.715.

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A commercial Mg alloy, AZ31B, has been used widely. In the texture of AZ31B sheet, each grain has its c-axis almost parallel to the sheet normal. Therefore, at the bending process of the sheet, basal slip system can not accommodate an in-plane plastic strain which is perpendicular to the c-axis of each grain. It is known that {10―,12} twin can be formed by applying an extension strain parallel to the c-axis, which is equivalent to the a-axis compression strain. So in the bending deformation of the AZ31B sheet with a texture microstructure, it is expected that {10―,12} twinning occurs. In this study, an in-situ bending test of AZ31B sheet with a texture was conducted under a confocal scanning laser microscope to observe twinning by applying compression stress along a direction almost perpendicular to the c-axis of grains. In addition, EBSD techniques were used for the analysis of crystal orientations. The process of twin development observed by the in-situ bending test can be summarized as follows; with the increase of the deformation strain, the total area of twins increases. However, it is noted that the growth of twins is apparent while the number of twins is almost constant during plastic bending deformmation. EBSD analysis suggested that twinning behavior obey Schmid’s law even in the polycrystal.

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25

Kulakov, Mykola, Jianglin Huang, Michail Ntovas, and Shanmukha Moturu. "Microstructure Evolution During Hot Deformation of REX734 Austenitic Stainless Steel." Metallurgical and Materials Transactions A 51, no. 2 (December 4, 2019): 845–54. http://dx.doi.org/10.1007/s11661-019-05558-6.

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AbstractMechanical properties of a REX734 austenitic stainless steel were examined through compression testing over a wide range of temperatures (1173 K to 1373 K (900 °C to 1100 °C)) and strain rates (0.1 to 40 s−1) that cover deformation conditions encountered in different metalworking processes. The evolution of microstructure was studied using electron microscopy combined with electron backscatter diffraction and energy-dispersive spectroscopy. Partially recrystallized microstructures were obtained after compression testing at 1173 K (900 °C), while after deformation at 1273 K and 1373 K (1000 °C and 1100 °C), the material was fully recrystallized almost in all examined cases. The role of dynamic and metadynamic restoration processes in the formation of final microstructure was investigated. Σ3 twin boundaries lost their twin character and transformed into general high-angle grain boundaries as a result of deformation, while during recrystallization new Σ3 twin boundaries formed. The evolution of precipitates during compression testing and their role in the recrystallization process was also discussed.

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26

WURMEL, J., and J. SIMMIE. "CFD studies of a twin-piston rapid compression machine." Combustion and Flame 141, no. 4 (June 2005): 417–30. http://dx.doi.org/10.1016/j.combustflame.2005.01.015.

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27

SHEN, Jiubing. "Experimental Study of a Mechanical Vapor Compression Wastewater Distillation System using Twin Screw Compressor." Journal of Mechanical Engineering 52, no. 10 (2016): 185. http://dx.doi.org/10.3901/jme.2016.10.185.

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28

Shen, Jiubing, Ziwen Xing, Kai Zhang, Zhilong He, and Xiaolin Wang. "Development of a water-injected twin-screw compressor for mechanical vapor compression desalination systems." Applied Thermal Engineering 95 (February 2016): 125–35. http://dx.doi.org/10.1016/j.applthermaleng.2015.11.057.

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29

Tomé, Carlos, and George C. Kaschner. "Modeling Texture, Twinning and Hardening Evolution during Deformation of Hexagonal Materials." Materials Science Forum 495-497 (September 2005): 1001–6. http://dx.doi.org/10.4028/www.scientific.net/msf.495-497.1001.

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Hexagonal materials deform plastically by activating diverse slip and twinning modes. The activation of such modes depends on their relative critical stresses, function of temperature and strain rate, and the orientation of the crystals with respect to the loading direction. For a constitutive description of these materials to be reliable, it has to account for texture evolution associated with twin reorientation, and for the effect of the twin barriers on dislocation propagation and on the stress-strain response. In this work we introduce a model for twinning which accounts explicitly for the composite character of the grain, formed by a matrix with embedded twin lamellae which evolve with deformation. Texture evolution takes place through reorientation due to slip and twinning. The role of the twins as barriers to dislocations is explicitly incorporated into the hardening description via a directional Hall-Petch mechanism. We apply this model to the interpretation of compression experiments both, monotonic and changing the loading direction, done in rolled Zr at 76K.

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Alharbi, Hamad F., Monis Luqman, Ehab El-Danaf, and Nabeel H. Alharthi. "Experimental and Numerical Study of Texture Evolution and Anisotropic Plastic Deformation of Pure Magnesium under Various Strain Paths." Advances in Materials Science and Engineering 2018 (2018): 1–12. http://dx.doi.org/10.1155/2018/2867281.

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The deformation behavior and texture evolution of pure magnesium were investigated during plane strain compression, simple compression, and uniaxial tension at room temperature. The distinctive stages in the measured anisotropic stress-strain responses and numerically computed strain-hardening rates were correlated with texture and deformation mechanisms. More specifically, in plane strain compression and simple compression, the onset of tensile twins and the accompanying texture-hardening effect were associated with the initial high strain-hardening rates observed in specimens loaded in directions perpendicular to the crystallographic c-axis in most of the grains. The subsequent drop in strain-hardening rates in these samples was correlated with the exhaustion of tensile twins and the activation of pyramidal <c+a> slip systems. The falling strain-hardening rates were observed in simple compression and plane strain compression with loading directions parallel to the c-axis where the second pyramidal <c+a> slip systems were the only slip families that can accommodate deformation. For uniaxial tension with the basal plane parallel to the tensile axis, the prismatic <a> and second pyramidal <c+a> slips are the main deformation mechanisms. The predicted relative slip and twin activities from the crystal plasticity simulations clearly showed the effect of texture on the type of activated deformation mechanisms.

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Korchuganov, Aleksandr, Dmitrij Kryzhevich, and Konstantin Zolnikov. "Nucleation of twins and dislocations in V-Ti alloys under various straining conditions." EPJ Web of Conferences 221 (2019): 01023. http://dx.doi.org/10.1051/epjconf/201922101023.

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The features of plasticity nucleation in V-4Ti and V-16Ti crystallites under uniaxial tension and bilateral compression are studied. It is shown that the nucleation of plasticity in crystallites is associated with the formation of twins under uniaxial tension. During the development of plasticity, a screw dislocation cell structure is formed between twin plates. The strain and stress at which plasticity nucleates in the material decreases with increasing Ti concentration. It was found that the distribution pattern of Ti atoms in the initial structure has a significant effect on the elastic limit of the simulated crystallites. The plastic deformation of crystallites with 16% Ti under bilateral compression is realized only by the dislocation mechanism. This behavior of the material is due to the low value of the stress at the elastic limit, which is insufficient for the formation of twins.

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32

Qin, Fengming, Yajie Li, and Jianjun Zheng. "The Activation and Evolution of Twinning during Bending of Friction Stir Welded AZ31 Magnesium Alloys." Metals 10, no. 1 (January 16, 2020): 139. http://dx.doi.org/10.3390/met10010139.

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AZ31 magnesium alloy joints obtained by friction stir welding with rotation speed of 1400 rpm and welding speed of 200 mm/min were subsequently subjected to the three-point bending process. The bending behavior, microstructure evolution and twinning mechanism were investigated. The results indicate that the stress-strain curve appeared as power-law shape during tension and the stress-strain curve appeared as work hardening shape during compression. However, the stress-strain curve during bending is different and macrographs of face and base bending indicated that the severe strain localization was present during bending of FSWed AZ31 magnesium alloy joint. Three concave regions formed due to texture distribution and stress state in the weld zone. In those regions, the grains had favorable orientation with c-axis parallel to the direction of tensile stress and abundant twins were activated. It can be proved by electron backscatter diffraction (EBSD) analysis—two twinning mechanisms were activated during bending—that is, ~56° { 10 1 ¯ 1 } contraction twin and ~86° { 10 1 ¯ 2 } expansion twin, in which { 10 1 ¯ 2 } twinning was main plastic deformation mechanism of joint and the number of twins was proportional to the compressive stress in corresponding areas. The twinning resulted in lattice rotation about 86° around < 1 2 ¯ 10 > direction and changed the orientation distribution of original crystal.

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33

Lee, W. S., R. H. Ma, W. F. Wu, S. L. Chen, and H. W. Hsia. "Performance and Bearing Load Analysis of a Twin Screw Air Compressor." Journal of Mechanics 15, no. 2 (June 1999): 69–78. http://dx.doi.org/10.1017/s1727719100000344.

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ABSTRACTTo study the performance and estimate the oscillating bearing loads of a twin screw air compressor, a theoretical model is proposed in this paper. Based on the model, a computer simulation program is developed and effects of different design parameters such as rotor profile, geometric clearance, oil injected position, oil temperature, oil flow rate and other operational conditions are investigated. Output variables such as bearing loads, specific power, compression efficiency, volumetric efficiency, discharge temperature are obtained. Some of the results are then compared with experimentally measured data, and good agreements are found between the simulation results and the measured data.

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34

Choi, Shi Hoon, Y. S. Song, Jong Kweon Kim, B. J. Jung, and Yong Bum Park. "Implementation of Twin Reorientation and Softening Schemes in a Polycrystal Plasticity Model for Mg Alloys." Materials Science Forum 558-559 (October 2007): 1063–68. http://dx.doi.org/10.4028/www.scientific.net/msf.558-559.1063.

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Uniaxial compression tests on hot-rolled AZ31 Mg alloy were carried out at a temperature of 300°C. In order to investigate work hardening and texture evolution during plastic deformation, cylindrical specimens were compressed to the rolling direction. Experimental investigation reveals that flow curves are strongly dependent on microstructure evolution such as deformation twinning and softening phenomenon. The occurrence of deformation twinning and softening phenomenon was revealed by the observation of microtexture using electron backscatter diffraction (EBSD). A visco-plastic self-consistent (VPSC) polycrystal model was used to simulate the work hardening, softening and texture evolution during the uniaxial compression. In order to calculate orientation of deformation twins, predominant twin reorientation (PTR) scheme was implemented into the polycrystal model. A softening scheme was also implemented in the polycrystal model to predict softening phenomenon and texture evolution after a peak stress.

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35

Groza, Doru, and Dan Mihai Dogariu. "Investigation on the Intake Process for a Theoretical Twin Opposite Piston Compressor Using R744 Refrigerant." Applied Mechanics and Materials 823 (January 2016): 75–78. http://dx.doi.org/10.4028/www.scientific.net/amm.823.75.

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This study aims to validate the use of R744 for a resonant twin piston compressor for domestic applications. The vapor-compression refrigeration is the most commonly approached method for cooling household appliances such as refrigerators and air conditioning systems. The R134a refrigerant is one of the most suitable refrigerants from an energetic point of view. R744 (CO2) compressors are less efficient, but the fact that the R134a raises serious environmental issues pushes commercial trend towards the usage of R744 [1]-[3]. Use of R744 in household appliances is currently an open topic and no company has switched yet to the environmental-friendly alternative. In this paper the fill efficiency will be simulated in order to validate if a conventional compressor such as the opposite twin piston compressor is capable of filling with refrigerant when operating at a 50Hz frequency. Such a validation can enable further investigations regarding the replacement of R134a with R744.

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Fleming, J. S., Y. Tang, and G. Cook. "The twin helical screw compressor Part 2: A mathematical model of the working process." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 212, no. 5 (May 1, 1998): 369–80. http://dx.doi.org/10.1243/0954406981521295.

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Part 1 of this paper describes the physical characteristics, applications and analytical procedures currently relevant to the twin helical screw compressor. Part 2, presented here, describes a mathematical model of the working process of the machine. Use is made of a geometric model developed by Tang [2] which describes all the essential features as functions of the male rotor angle of rotation. The following effects are taken into account: internal leakage through six paths, gas—oil heat transfer, injected liquid refrigerant flashing in the compression cavity, dissolved refrigerant flashing from the oil injected into the compression cavity, dissolved refrigerant flashing in the end casings from oil supplied to the bearings and the draining of flashed refrigerant gas from the end casings to the low-pressure regions of the main casing. Internal friction at the principal rubbing surfaces is taken to cause heating of the oil and is modelled by making use of extensive measured data and manufacturers’ information. The hotter oil influences the compression process via a changed gas—oil heat transfer rate. The gas-oil heat transfer coefficient and the internal leakage coefficients are determined from measured data for mid-range conditions and applied over a range of conditions. The model output is compared with measured data; its current accuracy and possible improvement are commented upon.

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37

Zhang, Chen, Dongsheng Li, Xiaoqiang Li, and Yong Li. "An Experimental Study of the Tension-Compression Asymmetry of Extruded Ti-6.5Al-2Zr-1Mo-1V under Quasi-Static Conditions at High Temperature." Metals 11, no. 8 (August 17, 2021): 1299. http://dx.doi.org/10.3390/met11081299.

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The tension-compression asymmetry (TCA) behavior of an extruded titanium alloy at high temperatures has been investigated experimentally in this study. Uniaxial tensile and compressive tests were conducted from 923 to 1023 K with various strain rates under quasi-static conditions. The corresponding yield stress and asymmetric strain hardening behavior were obtained and analyzed. In addition, the microstructure at different temperatures and stress states indicates that the extruded TA15 profile exhibits a significant yield stress asymmetry at different testing temperatures. The flow stress and yield stress during tension are greater than compression. The yield stress asymmetry decreases with the increase in temperature. The alloy also exhibits TCA behavior on the strain hardening rate. Its mechanical response during compression is more sensitive than tension. A dynamic recrystallization phenomenon is observed instead of twin generated in tension and compression under high-temperature quasi-static conditions. The grains are elongated along the tensile direction and deformed by about 45° along the compressive load axis. Finally, the TCA of Ti-6.5Al-2Zr-1Mo-1V (TA15) alloy is due to slip displacement. The tensile deformation activates basal <a>, prismatic <a> and pyramidal <c + a> slip modes, while the compressive deformation activates only prismatic <a> and pyramidal <c + a> slip modes.

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38

Subramanian, Raja, and Kenneth S. Vecchio. "Dislocation structures and twinning in tungsten <110> single crystals." Proceedings, annual meeting, Electron Microscopy Society of America 50, no. 1 (August 1992): 40–41. http://dx.doi.org/10.1017/s0424820100120606.

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Tungsten single crystals are brittle due to predominant twinning and crack formation at twin-twin intersections. Twinning and its influence on crack nucleation have been studied in detail. Despite the twinning, significant plastic deformation takes place by the generation and glide of dislocations. Hitherto uninvestigated dislocation structures and twin boundaries in tungsten <110> single crystals deformed quasistatically in compression have been studied using transmission electron microscopy.In compressed samples, cracks nucleate at twin-boundary intersections. Such a crack is indicated by an arrowhead in Figure 1 which shows an optical image of twin boundaries. Figure 2 shows a bright field (BF) image of a twin boundary (marked by an arrowhead). The inset in Figure 2 is the microdiffraction pattern taken at the twin boundary which shows a ∑3 coincidence site lattice (CSL) symmetry.

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39

Muránsky, Ondrej, Matthew R. Barnett, David G. Carr, Sven C. Vogel, and E. C. Oliver. "Combined In Situ Neutron Diffraction and Acoustic Emission of Twin Nucleation & Twin Growth in Extruded ZM20 Mg Alloy." Materials Science Forum 652 (May 2010): 149–54. http://dx.doi.org/10.4028/www.scientific.net/msf.652.149.

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In the present work in situ neutron diffraction and acoustic emission were used concurrently to study deformation twinning in two ZM20 Mg alloys with significantly different grain sizes at room temperature. The combination of these techniques allows differentionation between the twin nucleation and the twin growth mechanisms. It is shown, that yielding and immediate post-yielding plasticity in compression is governed primarily by twin nucleation, whereas the plasticity at higher strains is governed by twin growth. The current results further suggest that yielding by twinning happens in a slightly different manner in the fine-grained as compared to the coarse-grained alloy.

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40

Jiang, Yan, Yu'an Chen, and Gentao Gao. "Role of volume fraction of second phase particles, dislocation-twin and twin-twin interactions in the reduced tension-compression yield asymmetry." Materials & Design 97 (May 2016): 131–37. http://dx.doi.org/10.1016/j.matdes.2016.02.079.

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41

Wan, Gang, and Bao Lin Wu. "Effects of Texture on the Fracture Mechanism of AZ31 Magnesium Alloy under Dynamic Impact." Applied Mechanics and Materials 598 (July 2014): 98–101. http://dx.doi.org/10.4028/www.scientific.net/amm.598.98.

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the hot extruded AZ31 magnesium alloy which has basal texture was impacted along different direction and different fracture mode appeared. Under different impacted direction, the basal slip, prismatic slip, pyramidal slip, compression twin and tension twin have different critical resolved shearing stress (CRSS) and Schmid factor. Then different deformation modes were activated and resulted to different fracture modes.

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42

Chen, Xue, Yongjun He, and Ziad Moumni. "Twin boundary motion in NiMnGa single crystals under biaxial compression." Materials Letters 90 (January 2013): 72–75. http://dx.doi.org/10.1016/j.matlet.2012.08.107.

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43

Morris, J. R., Y. Y. Ye, K. M. Ho, C. T. Chan, and M. H. Yoo. "Structures and energies of compression twin boundaries inhcpTi and Zr." Philosophical Magazine A 72, no. 3 (September 1995): 751–63. http://dx.doi.org/10.1080/01418619508243798.

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44

Zhou, Ping, Dawu Xiao, Chunli Jiang, Ge Sang, and Dongli Zou. "Twin Interactions in Pure Ti Under High Strain Rate Compression." Metallurgical and Materials Transactions A 48, no. 1 (November 3, 2016): 126–38. http://dx.doi.org/10.1007/s11661-016-3832-9.

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45

Lee, W. S., R. H. Ma, S. L. Chen, W. F. Wu, and H. W. Hsia. "Numerical Simulation and Performance Analysis of Twin Screw Air Compressors." International Journal of Rotating Machinery 7, no. 1 (2001): 65–78. http://dx.doi.org/10.1155/s1023621x01000069.

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A theoretical model is proposed in this paper in order to study the performance of oil-less and oil-injected twin screw air compressors. Based on this model, a computer simulation program is developed and the effects of different design parameters including rotor profile, geometric clearance, oil-injected angle, oil temperature, oil flow rate, built-in volume ratio and other operation conditions on the performance of twin screw air compressors are investigated. The simulation program gives us output variables such as specific power, compression ratio, compression efficiency, volumetric efficiency, and discharge temperature. Some of the above results are then compared with experimentally measured data and good agreement is found between the simulation results and the measured data.

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46

Vlăducă, Iulian, Claudia Borzea, Dan Ionescu, Alexandra Ţăranu, Răzvan Ciobanu, Vicenţiu Ringheanu, and Răzvan Nedelcu. "Compressed air energy storage facility with water tank for thermal recovery." E3S Web of Conferences 180 (2020): 02002. http://dx.doi.org/10.1051/e3sconf/202018002002.

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The paper presents the prototype of the first Romanian Compressed Air Energy Storage (CAES) installation. The relatively small scale facility consists of a twin-screw compressor, driven by a 110 kW threephase asynchronous motor, which supplies pressurized air into a 50m3 reservoir, of 20 bar maximum pressure. The air from the vessel is released into a twin-screw expander, whose shaft spins a 132 kW electric generator. The demonstrative model makes use of a 5m3 water tank acting as heat transfer unit, for minimising losses and increasing efficiency and the electric power generated. Air compression and decompression induce energy losses, resulting in a low efficiency, mainly caused by air heating during compression, waste heat being released into the atmosphere. A similar problem is air cooling during decompression, lowering the electric power generated. Thus, using a thermal storage unit plays an essential role in the proper functioning of the facility and in generating maximum electric power. Supervisory control and data acquisition is performed from the automation cabinets. During commissioning tests, a constant stable power of around 50 kW with an 80 kW peak was recorded.

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47

Zhang, Youwei. "Results for Twin Singular Nonlinear Problems with Damping Term." International Journal of Mathematics and Mathematical Sciences 2011 (2011): 1–13. http://dx.doi.org/10.1155/2011/416173.

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By using the functional type cone expansion and compression fixed-point theorem in cones, some new and general results on the existence of positive solution for twin singular boundary value problems with damping term are obtained. An example is given to illustrate our results.

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48

Wang, Shou Ren, Li Ying Yang, Ru Ma, and Pei Quan Guo. "Fracture Failure Analysis of Twin Rolling Casting Magnesium by Hot Compression." Advanced Materials Research 123-125 (August 2010): 547–50. http://dx.doi.org/10.4028/www.scientific.net/amr.123-125.547.

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The flow stresses of AZ41M and ZK 60 wrought magnesium alloys under the deformation conditions of twin rolling casting and hot compression (TRC-HC) at different temperature and strain rates were studied. The deformation behavior and failure mechanism of them were discussed. The microstructure evolutions were analyzed by OM and EBSD technique. The results indicated that AZ41M and ZK 60 have different strain-stress curve under the same conditions. Working hardening results in occurrence of cracks in or around the shear bands. The recrystallized, equiaxed and fined grains in shear bands attribute to recovery and recrystallization, grains refinement causes local working hardening as well as decreases of crack tip driving forces. The stresses concentrate in shear bands causing cracks initiation and propagation. Casting defects to be the nucleus of cracks is another failure mode. With the increases of strains, dislocations rearrange forming sub-grains, the low angle grain boundaries (LAGBs) continuously evolved into high angle grain boundaries (HAGBs).

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HUANG, Hongtao, Wei LIU, Godfrey A., Ruihe TANG, and Qing LIU. "STUDY OF TWIN BEHAVIOR DURING UNIAXIAL COMPRESSION OF AZ31 MAGNESIUM ALLOY." Acta Metallurgica Sinica 48, no. 3 (2012): 357. http://dx.doi.org/10.3724/sp.j.1037.2011.00587.

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Hodge, A. M., T. A. Furnish, C. J. Shute, Y. Liao, X. Huang, C. S. Hong, Y. T. Zhu, T. W. Barbee Jr., and J. R. Weertman. "Twin stability in highly nanotwinned Cu under compression, torsion and tension." Scripta Materialia 66, no. 11 (June 2012): 872–77. http://dx.doi.org/10.1016/j.scriptamat.2012.01.027.

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Journal articles on the topic 'Compression twin'

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