Review on fracture and crack propagation in weldments – A fracture mechanics perspective

Many petroleum companies expand their activities further north towards the Arctic region, resulting in design temperatures down to −60• C, which is much lower than what is usual for most current petroleum installations. As properties of steels are temperature dependent, it is of great interest to evaluate the effects of low temperature on the crack driving force in steels. The present work investigates these effects numerically using finite element (FE) models of single-edge-notchedtension (SENT) specimens with crack depths 0.1 ≤ a/W ≤ 0.5. The effects of Lüders strain, yield strength and crack depth on the crack tip opening displacement (CTOD) and the relation between CTOD and crack mouth opening displacement (CMOD) are studied, and it is shown that an increase in yield strength and Lüders strain, as a result of Arctic temperature, intensifies the crack driving force. It is also shown that the crack depth has very little influence on the effect of Lüders strain on the CTOD. An approximate model that can be used to estimate the CTOD based on yield strength, Lüders strain and loading is proposed for gross stress levels σ G /σ y ≤ 0.5 and a crack depth a/W = 0.5. It is finally shown that the tensile properties have a more significant effect on the CTOD-CMOD relation than the crack depth for a SENT specimen.Mange petroleumsselskaper utvider sine aktiviteter nordover mot arktiske områder. Dette fører til designtemperaturer ned til −60• C, noe som er mye lavere enn det som er vanlig for de fleste nåvaerende petroleumsinstallasjoner. Ettersom egenskapene til stål er temperaturavhengige, er det av stor interesseå evaluere effektene av lav temperatur på den drivende kraften for sprekkvekst i stål. Dette arbeidet undersøker disse effektene numerisk ved hjelp av elementmetoden med modeller av single-edge-notched-tension (SENT)-bruddprøver med sprekkdybder 0.1 ≤ a/W ≤ 0.5. Effektene av Lüders tøyning, flytespenning og sprekkdybde på sprekkspissutvidelsen (CTOD) og sammenhengen mellom CTOD og sprekkmunningsutvidelsen (CMOD) er studert, og det er påvist at økt flytespenning og Lüders tøyning, som et resultat av arktisk temperatur, fører til økt drivende kraft for sprekkvekst. Det er også vist at sprekkdybden har liten innflytelse på effekten av Lüders tøyning på CTOD. Det er foreslått en omtrentelig modell som kan bli brukt tilå estimere CTOD basert på flytespenning, Lüders tøyning og last for bruttospenningsnivåer σ G /σ y ≤ 0.5 og sprekkdybde a/W = 0.5. Det er til slutt påvist at materialets strekkegenskaper har en større virkning på CTOD-CMOD-forholdet enn sprekkdybden for en SENT-prøve.i ii PrefaceThe work presented here is a Master's thesis written at Department of Engineering Design and Materials at Norwegian University of Science and Technology (NTNU). The thesis work is carried out as a part of SMACC (Studies of materials behavior for future cold climate applications), which is a research project with several industry partners, and with SINTEF and NTNU as research partners.The author wishes to thank SINTEF fo...

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“…The fracture toughness of steels is usually reduced when decreasing the temperature [5,10,[12][13][14]22].…”

Section: Introductionmentioning

confidence: 99%

Effect of low temperature tensile properties on crack driving force for Arctic applications

Dahl

Ren

Akselsen

et al. 2018

Theoretical and Applied Fracture Mechanics

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“…This is typically associated with a width W of the reduced section of about 2 mm [1,[5][6][7][8][9][10][11][12][13]. As seen in Figure 2, which compares the result of such a miniature tensile test (cross section of the reduced section: 2 mm x 0.5 mm) of a homogeneous material to a standard sized tensile test of the same material, there are clear but reasonable deviations in the stress-strain curve.…”

Section: 2mentioning

confidence: 99%

“…The most common method used to produce miniature tensile specimens is wire electro discharge machining ('wire EDM') [1,7,8,10,11,[13][14][15][16][17] (note that one study used water jet cutting [18]). The advantage of EDM over traditional machining processes is that it can produce the small work piece accurately and to close tolerances with very little wasted material.…”

Section: Tensile Testing Of Miniature Specimensmentioning

confidence: 99%

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Characterisation of weld heterogeneity through hardness mapping and miniature tensile testing

Bally

Waele

Verleysen

et al. 2015

SCAD

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Abstract:Welding is a widely adopted industrial process used for joining components. A fusion weld has a highly heterogeneous microstructure and characterisation of strength heterogeneity is difficult because of the potentially large variations over a limited distance. Hardness mapping and miniature tensile tests are two distinct approaches to this problem. This paper reports on the possibilities and limitations of both techniques. Hardness mapping is a well-documented procedure as opposed to miniature tensile testing, where the dimensions of the dogbone shaped specimens are smaller than what standards prescribe. A particular challenge is the measurement of strains in such small specimens. The authors have achieved this measurement by means of Digital Image Correlation (DIC). To that end, a sufficiently fine speckling method has been developed.Keywords: heterogeneity; hardness mapping; miniature tensile testing; DIC INTRODUCTIONWelding is one of the most common joining methods due to its generally high production speed and low associated costs. It is often associated with flexibility, integrity and reliability [1]. An example application showing the economic importance of welding is pipeline installation. Costs associated to fusion welding are estimated to make up 20% of the total cost of pipe laying. These include aligning the pipe sections, cleaning and grinding, welding, checking the weld for flaws and coating the weld [2].Notwithstanding the economical appeal of welding, the localized application of heat and melting results in a high susceptibility to material discontinuities, flaws and residual stresses, whose presence may lead to structural failure and lifetime reduction. The prediction of weld flaw acceptability ('structural integrity') is hampered by the potential presence of strongly heterogeneous microstructures. Modern day weld flaw assessment ignores this heterogeneity by assuming a homogeneous weld. As such, a generally accepted method to characterise weld heterogeneity does not yet exist. STATE OF THE ARTHeterogeneity is inherent to fusion welds, because in order to melt the weld metal and fuse it with the base metal, heat has to be locally applied. For thicker sections, weldments are created in several passes (deposition of multiple layers), resulting in a variety of zones undergoing a succession of particular heat cycles. The heat cycle determines what the microstructure transforms into, each structure having a different stress-strain response. Not only the weld metal is heterogeneous due to this, but the heat affected zone (HAZ) of the base metal (heated but non-melted metal in close vicinity of the weld) also transforms.Many conventional steel welds show a hardened HAZ due to the occurrence of stronger microstructures. In contrast, a broad range of high strength low alloy steels obtain their properties from a fine grain size, resulting from a specific heat treatment, often combined with mechanical deformation. These steels may show a softened HAZ due to grain coarsening. To quantify variations ...

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“…Many engineering manufacturing and structural construction processes inevitably introduce residual stresses in the engineering components. One example is the residual stress caused by the thermal cycles during the welding procedures [5]. It is well-known that the residual stress has a non-negligible impact on the fracture toughness of the material/structural component [5].…”

Section: Introductionmentioning

confidence: 99%

Residual Stress State in Single-Edge Notched Tension Specimen Caused by the Local Compression Technique

Huang¹,

Zhou²

2016

Archive of Mechanical Engineering

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Three-dimensional (3D) finite element analyses (FEA) are performed to simulate the local compression (LC) technique on the clamped single-edge notched tension (SE(T)) specimens. The analysis includes three types of indenters, which are single pair of cylinder indenters (SPCI), double pairs of cylinder indenters (DPCI) and single pair of ring indenters (SPRI). The distribution of the residual stress in the crack opening direction in the uncracked ligament of the specimen is evaluated. The outcome of this study can facilitate the use of LC technique on SE(T) specimens.

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Review on fracture and crack propagation in weldments – A fracture mechanics perspective

Cited by 180 publications

References 165 publications

Effect of low temperature tensile properties on crack driving force for Arctic applications

Effect of low temperature tensile properties on crack driving force for Arctic applications

Characterisation of weld heterogeneity through hardness mapping and miniature tensile testing

Residual Stress State in Single-Edge Notched Tension Specimen Caused by the Local Compression Technique

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