High Temperature Crack Growth Research Articles

Study of High Temperature Crack Initiation and Growth in Light Capturing Ribbon (LCR) PV Module Interconnection

The ribbon interconnection between solar cells (used for collecting current from solar cells) is a key PV module component and it highly affects the reliability of PV module as interconnection failure can lead to PV module performance. Light Capturing Ribbon (LCR) is a new type of interconnection to increase the efficiency of PV modules by reflecting the incident sun rays from the interconnection ribbon to the cell surface. This paper studies a comparison of the crack initiation and growth in the PV module interconnection due to the high-temperature manufacturing process between Light Capturing Ribbon (LCR) and Conventional Ribbon (CR). Extended Finite Element Method (XFEM) in ABAQUS software is employed to find the Crack Initiation Temperatures (CIT) and the Crack Growth Rate (CGR) for different configurations of PV module interconnection designs. The optimum solder, silver, and copper thickness for LCR interconnection are recognized as 20µm, 40µm, and 125-187.5µm, respectively, where this configuration experiences smaller cracks in the solder joint material rather than CR interconnection with the same cross-section area.

Characterizing high temperature crack growth behaviour under mixed environmental, creep and fatigue conditions

Components in high temperature plant could undergo failure due to combinations of fatigue, creep or oxidation/corrosion depending on the loading, temperature and environmental conditions. A novel and robust approach for a progressive failure modelling is presented in this paper which for the first time attempts to combine these failure mechanisms as time or cycle dependent processes. In this study, a combined multiaxial inter/transgranular crack growth model at the meso-scale level was proposed to conveniently deal with the various failure scenarios that may exist in plant components. The simulated crack under the combinations of time dependent creep and oxidation mainly propagated along grain boundaries initiating from the notch surface, exhibiting an irregular shapes with crack branching. Whereas under fatigue/oxidation condition, the crack grew in a transgranular manner. Furthermore, the role of creep, fatigue and oxidation on the failure life was dependent on the applied duration period at peak loads. Cracks were prone to nucleate in transgranular and then propagate in intergranular. There existed competitions between creep, fatigue and oxidation damage. Finally, the failure modes due to different damage mechanisms and loading conditions in the cases of creep-fatigue-oxidation were proposed. The calculated failure modes corresponded with those observed in engineering alloys.

Influence of dwell time on fatigue crack propagation in Alloy 718 laser welds

The introduction of welded assemblies in aerospace components aid in weight reduction, but also lead to an increased risk of defects. It is therefore important to analyze the high temperature crack growth resistance of such welds. The results from high temperature cyclic and dwell-fatigue testing of surface flawed Alloy 718 welds are presented here. An increasing temperature and application of a dwell time accelerate the crack growth and increase interaction with secondary phases. During cyclic loading at 550°C, there is little interaction with the microstructure during transgranular propagation, but the application of dwell times results in a mixture of transgranular propagation and intergranular cracking of boundaries between different dendrites. At 650°C, mixed intergranular and transgranular mode of crack growth is seen under both cyclic and dwell conditions. However, during dwell-fatigue the interfaces between the secondary arms of the same dendrite are also weakened, leading to an interfacial type of crack growth also in the intergranular parts.

Effect of intermittent unloading or reversed loading on high temperature crack growth behaviour of Grade 91 steel under constant tensile load

As a part of the efforts for developing a reliable assessment procedure for crack growth in high temperature components, crack growth tests at various loading conditions were performed on Grade 91 steel. 1T compact tension specimens of 20 mm thickness were kept under constant tensile load at 600°C, but periodically unloaded or reversely loaded to compressive side to observe these effects on deformation behaviour as well as crack growth behaviour. It was found that periodical reversed loading accelerates crack growth due to re-acceleration of inelastic deformation during load holding, but its extent was not as large as predicted by creep J-integral in a conventional way. The predictions were improved by introducing an additional parameter to take account of creep damage recovery which was caused by the excursion to compressive load.

High-temperature crack growth in a Ni-base superalloy during sustained load

The high-temperature sustained load crack growth behaviour of a Ni-base superalloy was investigated using a combination of mechanical testing in controlled atmosphere, fractographical and microanalytical investigations, and finite element modelling. The results show that the local crack front geometry is un-even on two scales – jaggedness on the scale of 100μm was observed in all specimens, whereas mm-scale waviness could occasionally be observed. The jaggedness can be explained by a percolation-type crack growth along weaker grain boundaries, whereas the large-scale waviness is presumably due to larger regions of the material having specific grain texture with high crack growth resistance. The un-even crack front is shown to potentially have considerable effects on the loading conditions at the crack tip, whereas ligaments of un-cracked material in the crack wake are deemed to have less effect on the crack tip loading due to their low area fraction. The ligaments fail intergranularly in the wake as the crack grows in the present case, as opposed to by creep fracture as previously proposed. Finally, the plastically deformed regions about the crack and crack tip are shown not to exhibit any elevated oxygen levels, implying that the damage in these regions is purely mechanical.

S0305-4-3 組合せ応力下における高温き裂成長に対する電気ポテンシャル法の適用(第2報) : 種々の高温疲労き裂形態に関する検討([S0305-4]計測・疲労強度)

Following the previous report, FE analyses on DC electrical potential drop (PD) method were conducted. In order to investigate the applicability of the PD method to high temperature crack growth under combined stress conditions, the effects of crack angle, crack opening displacement and crack bending on the PD were investigated computationally. The calibration of PD method for crack growth under combined stress conditions was formulated. This calibration was applied to the experimental results of high temperature fatigue crack growth tests for stainless steel SUS304 at 650℃. It was clarified that high temperature fatigue crack growth in both tensile type and shear type can be evaluated by this calibration of PD method.

Creep deformation and crack growth rates of a super α 2 titanium aluminide alloy

The influences of stress and temperature on creep deformation behavior and the creep crack growth rates of the super α 2 Ti 3Al alloy were investigated with respect to its safe application at high temperatures. In a temperature range of 1033–1093 K at low applied stress levels, the stress exponent was equal to 1.5. At an intermediate stress range (10 −3 < σ/ E < 3 × 10 −3), a stress exponent of 3.3 was observed. As the applied stress was increased, the stress exponent changed from 3.3 to 4.4. The high temperature crack growth rate of the Ti 3Al alloy can be correlated with stress intensity factor K rather than C∗ at 1033 K due to environmental embrittlement.

2333 一方向凝固Ni基超合金の高温クリープ・疲労相互作用条件下でのき裂成長寿命則(S07-4 疲労き裂進展,S07 構造材料の疲労強度とき裂進展問題)

The Ni base directionally solidified super-alloy has been developed as a gas turbine blade material for high electrical efficiency power plant. Since turbine blades are faced with the centrifugal stress from the high-speed rotation, it is used under the high temperature creep condition. On the other hand, it is used under periodical condition caused by combustion gas. Therefore, the Ni base directionally solidified super-alloys are operated under the condition of high temperature creep-fatigue interaction. In this paper, high temperature crack growth tests were conducted under the condition of creep-fatigue interaction for the Ni base directionally solidified super-alloy, CM247LC. Based on the non-equilibrium science, crack growth mechanisms were investigated by analyzing the effects of cycle dependent and time dependent mechanisms on the crack growth behaviors under the condition of creep-fatigue interaction. Furthermore, the law-of crack growth life under the conditions of creep-fatigue interaction was derived.

2004 組合せ応力下における高温き裂成長に対する電気ポテンシャル法の適用(G03-1 測定・検出・評価技術(1),G03 材料力学)

2004 組合せ応力下における高温き裂成長に対する電気ポテンシャル法の適用(G03-1 測定・検出・評価技術(1),G03 材料力学)

High Temperature Crack Growth Behavior of 304 Stainless Steel under Creep and Fatigue Loading

The crack growth behavior in a 304 stainless steel has been investigated at 538°C in air environment. Compact tension specimens were subjected to fatigue, creep and creep-fatigue loading. The combined effects on crack growth rates of load level and hold time have been examined. Stress intensity factors are found to correlate crack growth rates reasonably well for fatigue crack growth. Creep crack growth rates are found to correlate with stress intensity factor and C*(t). Crack growth rates under hold time cycles are successfully correlated with C*(t)avg under various load levels and hold times. Crack growth under creep-fatigue loading has been simulated by elastic-plastic-steady state creep finite element analyses. The results of analysis show that fatigue loading interrupts stress relaxation around the crack tip during hold time and causes stress reinstatement, thereby giving rise to accelerated crack growth compared with crack growth under static loading. Analysis of hold time crack growth based on the cyclic stress-strain response yields crack closure during unloading, and creep deformation during hold time tends to lower the closure load.

Effect of Cavity Growth Rate and Cr on High Temperature Crack Growth in P92 and P122 Steels

In this work, the velocity of crack propagation at high temperature was investigated with da / dt - C t relationship using recently developed P92 and P122 steels. Role of cavity in crack growth rate and load line displacement rate was studied by measuring the cavity size and density, which will influence crack nucleation and growth. Since temperature and stress changes are particularly important at high temperature, crack growth behavior was evaluated under various temperature and K i(initial stress intensity factor). Effect of Cr content was evaluated by measuring crack growth activation energy in thesis.

Creep crack growth testing of P91 and P22 pipe bends

Laboratory component tests play an important role in the development of life assessment procedures for high temperature crack initiation and growth. Thus, the working programme of the project BE 1702 HIDA, which addressed the validation, expansion and harmonisation of existing procedures for high temperature defect assessment, included a comprehensive experimental programme with feature tests of components as its core. Because of their relevance for the high temperature industry, P91 and P22 were included in HIDA among five materials. This paper presents laboratory creep crack growth tests of P91 and P22 pipe bends, discusses the test experience and draws some conclusions for laboratory component tests in general. The components were prepared with spark-eroded notches at the outer surface. The test temperature was 625°C for P91 and 565°C for P22.

Fractographic failure analysis of brittle materials

The fracture characteristics of two groups of brittle materials (structural ceramics and silicide based materials) produced by PM technology and developed for high-temperature applications are reviewed from the viewpoint of fractography. The main observation techniques and fracture-mechanical relations are summarised. The relationship between strength, fracture origins, defects and the relationship between fracture toughness and fracture micromechanisms and microstructure are described. The fractographic appearance of the high-temperature crack growth and creep failure is characterised. The possibilities for improving the fracture toughness and high-temperature properties are discussed.

Fractography and fracture mechanics property assessment of advanced structural ceramics

Fracture characteristics and mechanical properties of advanced structural ceramics produced by advanced technology and developed for high temperature applications are reviewed from the viewpoint of fractography. The main processing routes for preparation of in situ reinforced ceramic matrix composites, nanocomposites, and laminar/layered composites are summarised and their principal microstructure parameters are described. The main observation techniques, levels/steps of observation, and principal fracture mechanics relations are summarised. The relationships between rupture strength, Weibull modulus, and defect distribution, and the possibilities for strength improvement through improved processing, are discussed. Recent results relating to strength and reliability prediction are given. The fractographic appearances of process and bridging zone toughening mechanisms are described and the relationship between fracture toughness, microstructure, and fracture micromechanisms is discussed. Interfaces (macro- and microscale) and residual stresses and their effect on toughness, strength, and reliability of nano- and layered composites are analysed. The influence of loading mode on fracture and mechanisms leading to fatigue degradation in these materials is summarised. Fracture surface characteristics of high temperature crack growth and creep failure are described and the effects of oxidation and corrosive degradation on fracture and strength of these materials are considered. The role of fractography in the development of advanced ceramics and in efforts to improve reliability is described.

Influence of prior cyclic hardening on high temperature deformation and crack growth in type 316L (N) stainless steel

For power generating equipment subjected to cyclic loading at high temperature, crack growth could arise from the combinations of fatigue and creep processes. There is potential for the material to undergo hardening (or more generally changes of material state) as a consequence of cyclic loading. Results of an experimental study to examine the influence of prior cyclic hardening on subsequent creep deformation are presented for type 316L(N) stainless steel at 600°C. Experiments were also carried out to explore creep crack growth at constant load, and crack growth for intermittent cyclic loading. For the as-received material there is substantial primary creep (hardening) at constant load, while for the cyclically hardened material at constant load the creep curves show recovery, and increasing creep rate with increasing time. Specimens subjected to prior cyclic hardening were also used for a series of creep and creep-fatigue crack growth tests. These tests demonstrated that there was accelerated crack growth compared to crack growth in as-received material.

Effect of aluminide particle distribution on the high temperature crack growth characteristics of a Co-Ni-Fe superalloy

Inconel 783{reg_sign} is an oxidant-resistant, controlled coefficient of thermal expansion, cobalt-nickel-iron-based superalloy. The matrix ({gamma}) is FCC and can be strengthened by coherent strengthening precipitates ({gamma}{prime}). It has been shown that an aluminum content greater than 5 wt% leads to the formation of body-centered aluminide ({beta}) particles and improved resistance to stress accelerated grain boundary oxygen (SAGBO) embrittlement relative to other low-expansion superalloys. The study described below was undertaken to determine the role of the {beta} phase during creep crack growth, and how its distribution affects the alloy`s SAGBO resistance. Aging of alloy 783 to produce a continuous grain boundary film of {beta} phase results in reduced creep crack growth rates at 538 C compared to heat treatments which do not result in a continuous film. Oxidation studies indicate that the {beta} phase is oxidation resistant and hence may cause increased resistance to SAGBO.

High-temperature crack growth in Y-TZP

Fatigue and static crack growth is studied in Y-TZP at intermediate temperatures. Fractographic observations indicate that a reduction in interfacial fracture energy, which induces intergranular fracture at intermediate temperatures, is responsible for a decrease in crack propagation thresholds and fracture toughness. Static and cyclic growth rates increase with temperature. Although cyclic loading in the near-threshold regime promotes crack propagation, cyclic crack growth velocities for higher values of K are slower than predictions based upon static crack growth results.

Analysis of high temperature fatigue crack growth behavior

High temperature fatigue crack growth has been examined in the light of the new concepts developed by the authors. We observe that the high temperature crack growth behavior can be explained using the two intrinsic parameters ΔK and Kmax, without invoking crack closure concepts. The two-parameter requirement implies that two driving forces are required simultaneously to cause fatigue cracks to grow. This results in two thresholds that must be exceeded to initiate the growth. Of the two, the cyclic threshold part ΔK∗th is related to the cyclic plasticity, while the static threshold K∗max is related to the breaking of the crack tip bonds. It is experimentally observed that the latter is relatively more sensitive to temperature, crack tip environment and slip mode. With increasing test temperature, the cycle-dependent damage process becomes more time-dependent, with the effect that crack growth is dominated by Kmax. Thus, in all such fracture processes, whether it is an overload fracture or subcritical crack growth involving stress corrosion, sustained load, creep, fatigue or combinations thereof, Kmax (or an equivalent non-linear parameter such as Jmax) remains as one essential driving force contributing to the final material separation. Under fatigue conditions, cyclic amplitude ΔK (or an equivalent non-linear parameter like ΔJ) becomes the second necessary driving force needed to induce the characteristic cyclic damage for crack growth. Cyclic damage then reduces the role of Kmax required for crack growth at the expense of ΔK.

High-temperature crack growth in 304 stainless steel under mixed-mode loading conditions

High-temperature crack growth experiments have been conducted with 304 stainless steel specimens under mode I, mode II, and mixed-mode conditions. Crack growth rate and direction data for three different mixed-mode loadings have been analyzed to investigate the factors that control crack growth under mixed-mode conditions. The value of C* was calculated for mode mixities ranging from pure tensile to pure shear loading at the crack tip using a reference stress approach. Effective values of C* based on a damage mechanics approach were then calculated in an attempt to determine the multiaxial stress parameter that most accurately characterizes the stresses driving crack tip damage. The hydrostatic stress was found to be the stress parameter that best correlates the crack growth rate data for mode I, mode II, and mixed-mode loading conditions. The angle of growth for the mode I and mixed-mode conditions appears to be governed by both the maximum principal stress and the hydrostatic stress. However, the lack of tensile loads for mode II loading results in crack growth that is nearly collinear with the notch corresponding to the position of the maximum effective stress. Overall, the present results indicate that the hydrostatic stress is the most valid multiaxial stress parameter for predicting high-temperature crack growth in the present material under mixed-mode conditions.

High-temperature crack growth in 304 stainless steel under mixed-mode loading conditions

High-temperature crack growth in 304 stainless steel under mixed-mode loading conditions