Littérature scientifique sur le sujet « Produktutvikling og materialer »

I arbeidet med denne avhandlingen har det blitt utført et omfattende arbeid på ulike aspekter ved utviklingen av et monocoque chassis designet for å konkurrere i Formula Student. Analyse, dimensjonering og produksjon er hovedtema i denne oppgaven. Fokuset har ligget i å beskrive den tilnærmingen som brukes i designfasen, analyse og testing av lokaliserte laster på sandwichpaneler, samt utvikle en produksjonsprosess for chassiset. Alt av dimensjonering, analyse og testing er utført på sandwich paneler representativt for et monocoque chassis. Hovedfokuset har vært et racerbilchassis for Revolve NTNU, med tilhørende laster. Monocoque-chassiset er en selvbærende konstruksjon hvor hjuloppheng, girkasse, veltebøyler og andre innfestninger går direkte i chassiset som tar opp alle kreftene.Mye av arbeidet har blitt gjort i analyse og eksperimentell testing av lokaliserte laster på sandwich paneler med såkalte “inserts”, da dette er den mest brukte metoden for å overføre laster inn på et skjærsvakt sandwichpanel.Eksperimeter og testing har vært en stor del av denne avhandlingen. Den meste av teorien som er beskrevet og brukt i denne oppgaven er også basert på empiriske resultater. Mye av arbeidet har bestått av den faktiske produksjon av strukturen, og tilhørende måling og verifisering av strukturen.

<p>Micro Electro Mechanical Systems (MEMS) produced to date include IR detectors, accelerometers, pressure sensors, micro lenses, actuators, chemical sensors, gear drives, RF devices, optical processor chips, micro robots and devices for biomedical analysis. The track for tomorrow has already been set and products like 3D TV, physician on a chip, lab on a chip, micro aircraft and food safety sensors will be developed when the technology matures and the market is ready.</p><p>Todays MEMS fabrication is typically based around a silicon substrate and borrow batch fabrication processes from the IC industry. Many of the developed MEMS products have never left a laboratory environment because they are fragile in the macro environment. The way to deal with this is to provide proper packaging so that they can be handled. This poses one of the major challenges in the MEMS industry. Not many packaging techniques have been commercially developed for MEMS and companies that have overcome the packaging problems very seldom reveal their packaging techniques. Functional problems that could be associated with a MEMS structure are often amplified by the package. The reason for this is often associated with packaging stress. Packaging stress related problems is what has kept many promising products from emerging on the market. Even the commercially available pressure sensors and accelerometers have packaging stress problems, but most of them have been overcome. A first step towards solving these challenges is to localise, quantify and understand the critical packaging stresses that act in a packaged MEMS device.</p><p>The goal of this work was to understand how packaging stresses act in a plastic moulded MEMS chip. The work has been threefold; simulation of transfer moulding, static stress analysis of the plastic capsule after moulding and modelling of the piezo-resistive behaviour of a MEMS pressure sensor.</p><p>This dissertation is divided into 9 chapters. Chapter 1 introduces the concept of level-0 and level-1 packaging and looks at different techniques of obtaining the different packaging levels. It introduces the Small Outline Package (SOP) which is the package that has been simulated in this dissertation.</p><p>Chapter 2 gives the background in the theory that has been used to complete this work. It starts by discussing the chemistry and mechanics of thermosetting polymers. Then the rheological behaviour of Epoxy Moulding Compounds (EMC) in a transfer moulding process is discussed. </p><p>The experimental results from the thermomechanical material characterisation of the EMC are presented in Chapter 3. The material was found to have a Tg of 130^oC and coefficient of linear expansion of /oC and /oC below and above Tg respectively. It was further found that the material showed linear viscoelastic behaviour. Stress relaxation tests were run to obtain the relaxation coefficients needed for accurate modelling. The material was found to behave in a thermo rheologically simple manner and the WLF shift function was used to describe the time-temperature superposition principle.</p><p>Chapter 4 addresses the applicability of the plastic processing simulation code, C-Mold, for simulations of MEMS packaging in a SOP. It was found that the 2.5D simulation technique used by the software was inadequate for simulating the polymer filling of the SOP in question. This conclusion was drawn because 3D flow effect were observed in the moulding cavities. The cause for the 3D flow effect was the height of the SOP which was relatively large in order to accommodate for the MEMS device. However, the software proved to be very useful for balancing the runner system.</p><p>Chapter 5 starts with the development of a novel method for calculating the accurate piezoresistance for implanted silicon piezo-resistors. The method let each finite element in a piezoresistor region represent one resistor in a resistor network. The total resistance was then found by simple resistor summation. This method was then utilized on a silicon diaphragm pressure sensor, which had four piezo-resistors implanted into the top surface. The resistors on the diaphragm formed a Wheatstone bridge and the change in piezo-resistance, as a result of applied pressure and hence change in the stress field, was transformed into an electrical signal by proper post processing. The model was built from the design specifications of a commercially manufactured die. The results were compared to the production measurements and matched the data within one standard deviation. It was found that the level-0 package had an effect on the output signal. This work is believed to be the first to report an estimation of the distortion effect that a level-0 package has on a sensor signal with temperature.</p><p>Chapter 6 presents the model of the complete MEMS pressure sensor component encapsulated by EMC in a SOP. The EMC was treated as being elastic and temperature dependent. The method that was developed and calibrated in Chapter 5 was used as an indirect measure of the accuracy of the FEM model. It was evident that the package had a profound effect on the sensor signal. This was consistent with the actual measured data. The match of the signal data was not satisfactory. The signal values for two of the four service temperatures lay outside 3 standard deviations of the experimentally measured results. The estimated sensitivity of the die also fell outside 3 standard deviations for three of the four service temperatures.</p><p>A special vector plot was developed to understand how the pressure, or packaging stress, from the EMC effected the signal and sensitivity of the sensor die. The numerical simulations were done assuming a stress free temperature of 175^oC, the moulding temperature. The packaging stress was found to increase with decreasing temperature. This was the effect of the subsequent increase in ΔT as the service temperature decreased.</p><p>The signal at zero pressure was found to shift as a function of temperature. This was caused by the packaging stress and a corresponding stress-field-shift on the diaphragm. The origin for this shift was an uneven packaging stress between the front and the back side of the sensor die. At -7^oC, the pressure on the front and the back was 30 and 20MPa respectively. This caused an uneven bending moment on the membrane long sides and resulted in a shift in the stress field.</p><p>Chapter 7 elaborated the model one step further by treating the EMC as a viscoelastic material. The result of using the viscoelastic material model showed a reduction in the packaging stress due to stress relaxation. Viscoelastic materials are temperature and strain-history dependent. It was therefore necessary to run the model through the same processes posed by the manufacturing of the MEMS and SOPs. These included a set of thermocycles between -40^oC and 125^oC before the signals as a function of temperature and pressure were taken. The thermocycles were found to have a positive effect on signal shifting. Less signal distortion was seen with more cycles. The estimated and measured signal- vs. temperature-values matched within two standard deviations. The estimated sensitivities did not match the experimental measurements any better than those obtained for the elastic case. It was also found that sensitivity was nearly independent on packaging stress, but significantly dependent on pressure loading conditions.</p><p>The use of the viscoelastic model gave an improvement in simulated signal accuracy over the elastic model. It became clear that the EMC had to be treated as a viscoelastic material.</p><p>Chapter 8 concerned the change in material properties of the EMC and the impact this had on the FEM results. It was found that the behaviour of the MEMS pressure sensor was greatly affected by such changes.</p><p>Chapter 9 present the concluding remarks of this study.</p>

Sperre AS produserer i stor grad hele ROV konstruksjonen sin i aluminiumslegeringen AA6082-T6. Dette er et velegnet materiale for oppgava, men med noen mangler.Denne oppgava fokuserer p&#229; elektronikksylindrene til ROV-en, disse er per idag produsert i den ovennevnte aluminiumslegeringa. Man vil i framtida ned p&#229; store havdyp, ned mot 6000 meter. N&#229;r man skal s&#229; dypt vil disse elektronikksylindrene p&#229;f&#248;re konstruksjonen mye vekt og volum, b&#229;de direkte pga st&#248;rre masse aluminium og indirekte ved at man trenger mye oppdriftsmateriale.Ved &#229; benytte seg av kompositt og egna produksjonsmetode vil man kunne produsere samme tanken, med sv&#230;rt mye bedre egenskaper. I denne oppgava er det sett p&#229; metall-innerforing for spinning av kompositt p&#229; utsida og derfor oppn&#229; &#248;nska styrke, samt generelt design av sylinderen. Det er ogs&#229; foresl&#229;tt design uten innerforing, men da produsert ved hjelp av kompositt-duk. Hvilket materiale som er best egna til innerforing og hvilken kompositt som har de beste egenskapene er ogs&#229; vurdert.Som deloppgave er det utf&#248;rt mekanisk testing p&#229; sveist aluminiumslegering for &#229; verifisere DNV standardencite{DNV271}, samt vurdere om man ved forenkla varmebehandling kan gjenopprette noe av styrken til metallet.

The governing purpose of the thesis is to develop a chair concept based on a tilting mechanism called VAPAC. This chair concept has many potential ergonomic and environmental benefits that should be included and developed in the design. The report starts with an analysis of different segments within the chair market. Based on an evaluation, office chairs was chosen as the segment for the VAPA-Chair. Due to an interesting tilting idea suggested by the Supervisor/Concept originator, a test rig was built in order to try out a chair concept using straps for the tilting mechanism. This assignment was not originally one of the main tasks in the problem definition of this thesis . Due to curiosity and expectations for the idea, it was chosen to include this assignment in the thesis. A user survey reviled that this tilting idea offered an exciting and comfortable sitting experience. The concept using straps as tilting stringers was therefore developed further and important lengths and angles regarding the tilting mechanisms were settled. A problem occurred due to the risk of the chair tilting completely around if the user leans too much forwards or backwards in the chair. Making the stringers stiff so that they can withstand pressure when introduced to a load solved this problem. The tilting function was still the same as with the regular straps because the stringers were attached in joints, allowing the stiff straps to rotate freely. An Idea using turnbuckles as stringer was developed. This solution ensured the required stiffness as well as possibilities for height adjustment and a stop mechanism for the tilting. The terms &#147;Ergonomic&#148; and &#147;Environmental friendly&#148; is introduced, and important elements from these was set as requirements for the chair concept. Design sketches, doodling and brainstorming generated ideas for different concepts. Different functional concepts was introduced and evaluated as sub-parts of the chair. One concept was chosen for each part resulting in a holistic concept for the chair.The preliminary work results in a final concept, which is presented in the form of hand sketches and a 3D model using the program NX 7.5 Mechatronics . A lot of time was spent on modeling a simple and functional design with ergonomic and environmental friendly solutions.A material analysis was conducted regarding the bearing structure of the chair using the Life cycle analysis tool Eco-indicator 99. The analysis compared aluminum and steel. Due to low environmental impact using recycled aluminum, this material was chosen for the VAPA-Chair. A life cycle analysis was also conducted on the chair using the program CES Edupack. The analysis showed that the part of the chair&#146;s lifecycle that impacts the environment the most, is the production of materials. Based on these results, it is recommended that the VAPA-Chair should focus on weight optimization of the chair and use as much recycled aluminum as possible in the production. Based on results from the report, a list of recommendations for further work is presented.

Bakgrunnen for denne oppgaven er et &#248;nske fra tilhengerprodusenten Tysse om &#229; utvikle en mer effektiv metode for &#229; beregne levetid i forskjellige punkter p&#229; deres tilhengere. Dette skal gj&#248;res ved &#229; bruke strekklapper i stedet for destruktive metoder slik som brukes i dag. Motivasjonen er &#229; spare tid og penger. Masteroppgaven er basert p&#229; prosjektoppgaven skrevet av samme studenter semesteret i forveien. Da masteroppgaven startet var teknologi og utstyr unders&#248;kt og kj&#248;pt inn. Masteroppgaven skal ta dette utstyret til en fungerende l&#248;sning. Dette kan i grove trekk deles inn i f&#248;lgende punkter:&#149;Tilpassing av m&#229;leutstyr&#149;Materialtesting&#149;Utvikling av framgangsm&#229;teM&#229;leutstyret var kj&#248;pt og mottatt da masteroppgaven startet. Brokomplettering ble evaluert og en l&#248;sning ble valgt. Dette &#229;pnet for feils&#248;king, og for &#229; bli kjent med utstyret f&#248;r testing av utstyret mot testriggen hos Tysse. Bes&#248;ket bekreftet at valgt utstyr i prosjektoppgaven faktisk fungerte under forholdene. Kompletteringsenheter ble testet under realistiske forhold, noe som f&#248;rte til utvikling av et nytt, mer robust design. Festemekanisme for m&#229;leutstyret mot tilhengeren ble pr&#248;vd ut sammen med fuktsikringen. Etter bes&#248;ket hos Tysse ble det reservert tid i utmattingslaben der pr&#248;ver av st&#229;let i tilhengeren ble testet. Dette ble gjort for ytterligere &#229; sikre realistiske resultater fra levetidsberegningene. Pr&#248;ver ble maskinert, og materialstyrke ble funnet ved strekktesting. Strekktest og utmattingstest ble gjennomf&#248;rt basert p&#229; ISO standardene ISO 6892 og ISO 1099. Estimert SN kurve ble sammenliknet med data fra utmattingstestene. Framgangsm&#229;ten for testing av tilhengere ble revurdert i masteroppgaven. Den eksisterende metoden fra prosjektoppgaven ble satt opp mot en ny og enklere l&#248;sning som skulle bli bedre tilpasset Tysse. Programvaren for bearbeiding av datamateriale ble videreutviklet og ferdigstilt. Brukermanual som beskriver framgangsm&#229;ten steg for steg ble utviklet.Sluttresultatet ble levert til Tysse i Bergen med demonstrasjon og oppl&#230;ring av dem som skulle bruke systemet videre. Det ble ogs&#229; lagt fram et forslag til videref&#248;ring av systemet.

Gjennom dette arbeidet, er nanomekaniske kompresjonsegenskaper unders&#248;kt for tre forskjellige materialer: To st&#229;l legeringer og et renjern. Pillarer av varierende st&#248;rrelse, fra diameter 100nm til 2um, er fabrikkert ved bruk av FIB (Focused Ion Beam) i NTNU nanolab, etterfulgt av kompresjonstesting. Hvorvidt st&#248;rrelsen til pilarene p&#229;virker de mekaniske egenskapene, er gjennomg&#229;ende unders&#248;kt for alle tre materialene, med spesielt hovedvekt p&#229; en-krystall renjern. &#171;Small is stronger&#187; er et velkjent utsagn i micro skala verden, og er diskutert videre her for hvert materiale. F70 er en arktisk multifase st&#229;ltype, hvorp&#229; lokale egenskaper i korngrense og matrix er unders&#248;kt. Lokale soner i dette st&#229;let er korngrenser best&#229;ende av MA-partikler (Martensitt og rest-Austenitt) og matriksen som best&#229;r av fraksjoner av bainitt, martensitt, feritt og rest-austenitt. St&#229;let er varmebehandlet i to sykluser for &#229; simulere ICCGHAZ i sveisesoner, hvorp&#229; avkj&#248;lingshastigheten i temperatureintervallet fra T=800 - 500&#176;C er satt til 5 sekund for en pr&#248;ve, og 10 sekund for en annen pr&#248;ve. Avkj&#248;lingshastigheten avgj&#248;rer s&#229;ledes de bruddmekaniske egenskapene, som er unders&#248;kt ved nanomekanisk kompresjons testing. Pilar st&#248;rrelsen er 250nm, 450nm og 1um. Resultatet indikerer at 5 sekunds pr&#248;ven utviser h&#248;yere styrke og seighet. St&#248;rrelseseffekten er ikke fremtredende f&#248;r en kritisk pilar diameter p&#229; 250nm er n&#229;dd. Dette st&#229;let er unders&#248;kt som en del av prosjektet Arctic Materials Group p&#229; SINTEF.Et to-fase st&#229;l best&#229;ende av martensitt korn i en matriks av feritt er unders&#248;kt som en del av EU-prosjektet ved NTNU. To forskjellige pr&#248;ver er unders&#248;kt, hvorp&#229; forskjellen skyldes legeringsinnhold av 0.05wt% Nb i den ene pr&#248;ven, og ingenting i den andre. Legeringselementet &#248;ker b&#229;de duktile egenskaper og styrken, p&#229; grunn av finfordelte utfellinger av karbider og redusering av kornvekst. Single-slip orienteringen (5 2 11) i feritt fasen er i hovedfokus, men martensitt fasen er ogs&#229; unders&#248;kt. Fra resultatene kan det konkluderes med at innhold av Nb hever styrken og duktiliteten til materialet markant. Pillar diameter testet er 500nm og 1um. St&#248;rrelseseffekten kan ikke p&#229;vises eller avkreftes, da det ikke er unders&#248;kt nok pillar st&#248;rrelser til &#229; trekke en absolutt konklusjon. Tre forskjellige orienteringer av 99.998% rent bcc-Jern er unders&#248;kt: Multi-slip orientering (111) og (110), sammen med en single-slip orientering (235). Hovedfokuset ligger i &#229; unders&#248;ke st&#248;rrelseseffekten av en-krystall bcc-Fe, og om effekten av single-slip i forhold til multi-slip systemer p&#229;virker resultatene. Kompresjons testing avsl&#248;rer at det er en fremtredende st&#248;rrelseseffekt tilstede i alle tre orienteringer. Styrken til (111) orienteringen er h&#248;yere jevnt over sammenlignet med de to andre orienteringene, selv om st&#248;rrelseseffekten er mest fremtredende i (235). Den &#248;kte styrken som de minste pillarene utviser, er s&#229;ledes ikke p&#229;virket av mengden av tilgjengelige slip-systemer. En beskrivende ligning for st&#248;rrelses-effekt sensitiviteten er &amp;#964; = D-n, hvor st&#248;rrelsen p&#229; n indikerer sensitiviteten. For dette renjernet ligger verdien av n i samme omr&#229;det som for fcc metaller, alts&#229; en markant st&#248;rrelseseffekt. Skj&#248;nt, er deformasjons mekanismen i fcc og bcc grunnleggende forskjellige. Den observerte styrke &#248;kningen, konkluderes &#229; v&#230;re for&#229;rsaket av atermale prosesser, eller ved skru-dislokasjoners grad av mobilitet. Pillar st&#248;rrelsen varierer fra 100nm, 500nm, 1um og 2um. Det kan derfor konkluderes med at det er en sterk st&#248;rrelse effekt i bcc-Fe. For &#229; kunne forst&#229; de lokale egenskapene i komplekse mikrostrukturer, er det f&#248;rst og fremst avgj&#248;rende &#229; forst&#229; deformasjonsmekanismen i rene en-krystaller. En god teori for plastisk deformasion p&#229; sub-mikro niv&#229; er fremdeles ikke fremkommet og validert b&#229;de eksperimentelt og data simulert. N&#229;r dette skjer, kan man v&#230;re i stand til &#229; forst&#229; effekten av komplekse gitterstrukturer og legeringsinnhold, p&#229; nanomekaniske plastiske egenskaper. Med andre ord, man m&#229; tiln&#230;rme seg problemet fra en bottom-up perspektiv. Koblingen mellom datasimuleringer og eksperimentell testing p&#229; sub-mikroniv&#229;, m&#229; gj&#248;res sterkere. Inntil dags dato, er mye av dette universet fremdeles uutforsket, og kun mindre forst&#229;tt. Derfor kan du bruke denne oppgaven som ditt springbrett inn i verden av nanoskalerte materialeventyr!

Denne masteroppgaven bygger videre p&#229; samme problemstilling som i fordypningsprosjektet (TMM 4501)&#148;Analyse av Al-ekstrudering for &#229; forhindre rekrystallisasjon&#148;,h&#248;sten 2011.Oppgaven er gjennomf&#248;rt i samarbeid med Benteler Aluminum Systems Norway AS p&#229; Raufoss. Problemstillingen handler om u&#248;nsket grovrekrystallisering i aksesymmetrisk Al-ekstrudering ved senere prosessering. Det er gjennomg&#229;tt teori som tar for seg opphavet til forskjellige rekrystalliseringsfenomerer under varmdeformasjon av Al-legeringer. Teorien tar for seg fysiske og empiriske rekrystallisasjonsmodeller. Fysiske modeller er baset p&#229; kornvekst, dannelser av subkorn og korngrenseorienteringer. Empiriske modeller inkluderer parametere som temperaturer, t&#248;yninger, t&#248;yningshastigheter og ulike konstanter. I tillegg belyser teorien ulike ekstruderingsfors&#248;k og datasimuleringer av ulike varmformingsprosesser. Litteraturen har opphav fra ulike forskningsmilj&#248;er. Fra bes&#248;k hos Bentlers industrilokaler p&#229; Raufoss ble det tatt med ekstruderte Al-pr&#248;ver av aksesymmetrisk stangprofil tilbake til NTNU. P&#229; Verkstedtekniske laboratorier ble det kappet tre diskpr&#248;ver fra den samme aluminiumen. Deretter ble diskene slipt, varmebehandlet og etset for &#229; spore opp grovrekrystallisering i det ytre sjiktet av profilen.En simuleringsmodell fra fordypningsprosjektet har i denne oppgaven blitt forandret og tilpasset Bentelers st&#248;rste ekstruderingspresse P40. To stangprofiler med 80 og 43 mm i diameter ble simulert i Deform 2D.I Deform 3D ble det fors&#248;kt simulert en kompleks modell av to paralelle hulprofiler som brukes i bilkonstruksjoner. Fra simuleringsmodellene er det vist bilder med tilh&#248;rende forklaringer.Resultater fra unders&#248;kelsen av teori, skivepr&#248;ver og simuleringer er oppsummert og diskutert i eget kappittel.Rapporten er skrevet i Microsoft Word og datasimuleringer er gjennomf&#248;rt i Deform 2D og Deform 3D (versjon 10.2 og 11.0).

The purpose of this study was to explore the posibilities and challenges with simulating fatigue crack growth (FCG) by the extended finite element method (XFEM). Another aim was to develope a procedure for XFEM FCG simulations in Abaqus by means of scripting. Finally was the procedure used to simulate FCG in an API standard, cone shaped threaded connection. Different FCG models were reviewed by a limited litterature search and a procedure 2D FCG simulations was carried out by a python script. The procedure succeeded with the simulation of FCG when applied to a model with refined mesh around the crack tip. In the suggested partial tasks of the thesis description were a procedure 3D FCG simulation also suggested, but as this required more computer capacity than available in the study this was not carried out.

The goal of this Thesis is to verify a winning solution for the DNV Fuel Fighter 2, the verification of the design and development will be achieved by a series of verification, validation and testing activities.The Literature review of the report represents the VVT activities during the entire life cycle. The Theory and Methods used in the Thesis are based on A. Engel&#146;s &#147;Verification, Validation and Testing activities of Engineered Systems&#148;. The author has customized those VVT activities so they fit the time and resource constrains of the case of study.The case is the NTNU&#146;s fifth entrance to the Shell Eco Marathon competition, The DNV Fuel Fighter 2. The actual repot is a reflection of the first time in SEM&#146;s project where an entire Thesis reflects the VVT activities in order to qualify the vehicle.This Master Thesis follows the work that was done in the specialization project 2011 fall in the NTNU. The fall report was focused on the trade-off and requirement analysis and in the definition a high level architecture that could be use in the project. The project work was used as a foundation for the work that was done afterwards in this Master Thesis. The work done during the year is based on the systems engineering effort made from the previous year. The author along with the other system engineer of the project has upgraded the SE effort.The main contribution of the Thesis has been the development of the VVT activities and to prove that they are useful for projects with time and resource constrains. The suggested future work consists of continuing with the use of the VVT strategy performed this year and to upgrade it until the Acceptance stage; where the final user will be the responsible of performing the tests.

The main goal for this thesis has been to perform fatigue life predictions on large components.Dierent methods were to be chosen and reviwed critically. Experimental datafor girth welded pipes was assessed by means of a version of BS7910 which were modeledfrom scratch. This version was veried with results from CrackWise, and used to predictthe fatigue life for loade cases matching the selected experimental data. The fatigue assessmenttool P-FAT was used to predict the fatigue life for the same experimental data,and the results were compared. Except for some deviations recorded for embedded cracks,a generally good agreement was found between the two tools.Both the modeled BS7910 and P-FAT predicted conservative but accurate fatigue livesfor the experimental data that had signicant defects. They predicted non conservativeresults for specimens that did not have signicant defects, when the initial crack depthwas set to 0.1 mm. When the initial crack depth was set to 0.5 mm the modeled versionpredicted fatigue lives in agreement with the experimental results.Fatigue life predictions were also performed by assistance of S-N curves provided by DNVRP-C203.The results from these predictions were in agreement with the experimentaldata, except for four specimens. These four specimens had signicant aws, which reducedthe fatigue life signicantly.A review of a two-phase fatigue assessment model was made. This model uses a strainedbased approach to assess the fatigue crack initiation phase, and the fracture mechanicapproach suggested in the BS7910 to assess fatigue crack growth. This method haveshown promising results for fatigue assessment of llet welds in the literature, but themodel needs further investigation and calibration to be used to predict fatigue life ofgirth welded structures. A specic area to investigate is the proposed transition depth of0.1 mm. This depth is dubious based on the results