inelastic strain
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2022 ◽  
Vol 1213 (1) ◽  
pp. 012004
Author(s):  
D Yu Zhapova ◽  
A I Lotkov ◽  
V N Grishkov ◽  
A A Gusarenko ◽  
I S Rodionov

Abstract The paper presents the experimental results of studies of the temperature dependence of inelastic and plastic strains during torsion of coarse-grained samples of the Ti49.3Ni50.7 (at.%) alloy. Investigations of the deformation behavior of the test alloy samples in the martensitic, two-phase and high-temperature states have been carried out. It is shown that the value of the summary inelastic strain reaches a maximum value of ∼ 18% under deformation of the samples in the martensitic and two-phase state, as well as in the temperature range of pre-transition phenomena.


Buildings ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 562
Author(s):  
Basem S. Abdelwahed ◽  
Mosbeh R. Kaloop ◽  
Waleed E. El-Demerdash

The ductility and capacity of reinforced concrete beam-column connections depend mainly on the concrete’s strength and the provided reinforcements. This study investigates numerically the role of low-strength concrete in beam-column joints utilizing ABAQUS software. In this simulation, a newly developed stress-inelastic strain relationship for both confined and unconfined low-strength concrete is used. This study recommended a specific value of the concrete dilation angle for both substandard and standard joints. Also, stirrups’ yield strength value was found to play an insignificant role in improving the shear resistance of such joints with low-strength. In addition, the joint shear strength prediction using empirical models that implicitly consider the stirrups contribution in improving joint resistance was found to be better than the prediction of other models that explicitly consider the stirrups’ presence. The numerical results also showed that the use of a diagonal steel haunch as a joint retrofitting technique significantly increases the joint shear capacity and changes its brittle shear failure into a ductile beam flexural failure.


2021 ◽  
Author(s):  
Marta Kuczynska ◽  
Ulrich Becker ◽  
Youssef Maniar ◽  
Steffen Weihe

Abstract The reoccurring cyclic load imposed onto soldered electronic components during their operation time leads to accumulation of inelastic strains in the structure. On a microscale level, the degree of plastic deformation is determined by the formation and annihilation of dislocations, leading to continuous refinement by creation of new grain boundaries, precipitates relocation and growth. This microstructure rearrangement, triggered by an increasing amount of inelastic deformation, is defined as dynamic recrystallization. This work presents a macroscale modelling approach for the description of continuous dynamic recrystallization observed in Sn-based solder connections. The model used in this work describes kinetics of macroscopic gradual evolution of equivalent grain size, where the initial grain size is continuously refined with increasing accumulated inelastic strain until a saturation grain size is reached. The rate and distribution of dynamic recrystallization is further numerically modelled dependent on the effective accumulated inelastic strain and governing stress multiaxiality. A parameter study of the presented model and its employment in finite element (FE) simulation is further described. Finally, FE simulation of the grain size evolution is demonstrated on an example of a bulky sample under isothermal cyclic mechanical loading, as well as a BGA-like structure under tensile, shear and mixed mode cyclic load.


2021 ◽  
Vol 11 (21) ◽  
pp. 9983
Author(s):  
Yuebing Li ◽  
Yuxuan Song ◽  
Pan Liu ◽  
Ting Jin

To understand the premature-fracture mechanisms of long-term service damage of an advanced alloy’s (Chinese P92 steel) welded joint, the creep-fatigue (CF) experiments with holding times of 30, 120, 300, 600 and 900 s were individually performed at 923 K. The cyclic softening, inelastic-strain amplitudes and stress-relaxation behaviors were compared between welded and base-metal (BM) specimens. From the results, the failure stage of the welded specimens occupies 45% of the lifetime fraction, while it only takes up 20% of the lifetime fraction in BM specimens with short holding times (30 and 120 s). Furthermore, only two softening stages were observed for both kinds of CF specimens with long holding times. The absence of a third softening stage in longer-held specimens indicates that the processes of macroscopic-crack initiation, propagation and rupture were accelerated. Based on the observation of the fracture surfaces, the fracture mechanism shifted from fatigue-dominated damage to creep-fatigue interaction when the holding period was increased.


Author(s):  
Mitsuaki Kato ◽  
Takahiro Omori ◽  
Akihiro Goryu ◽  
Tomoya Fumikura ◽  
Kenji Hirohata

Abstract Power modules are being developed to increase power output. The larger current densities accompanying increased power output are expected to degrade solder joints in power modules by electromigration. In previous research, numerical analysis of solder for electromigration has mainly examined ball grid arrays in flip-chip packages in which many solder balls are bonded under the semiconductor device. However, in a power module, a single solder joint is uniformly bonded under the power device. Because of this difference in geometric shape, the effect of electromigration in the solder of power modules may be significantly different from that in the solder of flip chips packages. This report describes an electromigration analysis of solder joints for power modules using an electrical-thermal-stress coupled analysis. First, we validate our numerical implementation and show that it can reproduce the vacancy concentrations and hydrostatic stress almost the same as the analytical solutions. We then simulate a single solder joint to evaluate electromigration in a solder joint in a power module. Once inelastic strain appears, the rate of increase in vacancy concentration slows, while the inelastic strain continuously increases. This phenomenon demonstrates that elastic-plastic-creep analysis is crucial for electromigration analysis of solder joints in power modules. Next, the solder joint with a power device and a substrate as used in power modules was simulated. Plasticity-creep and longitudinal gradient generated by current crowding have a strong effect on significantly reducing the vacancy concentration at the anode edge over a long period of time.


2021 ◽  
Author(s):  
Ziauddin Mahboob

‘Natural’ fibrous material are subjects of accelerated research on account of the non-renewability and environmental costs of traditional ‘synthetic’ engineering fibres like Carbon and Glass. Of all candidates, Flax plant fibres have been found to offer composite reinforcement similar, or even superior, to Glass fibres in specific mechanical properties. Despite repeated evidence of its potential from independent studies, industry adoption of natural fibre reinforcement for load-bearing applications is still negligible, owing to their relatively immature body of research that discourages confidence in their long-term strength, durability, and predictability. This work contributes original findings on the complex damaged-condition response of natural fibre composites (NFC), and proposes modelling approaches to simulate the same. Material properties and mechanical behaviour of several Flax-epoxy composites are determined under tensile and compressive static loading, and correlated to internal damage mechanisms observed by micrography. Stiffness degradation and accumulated permanent strain are quantified along principal in-plane orthrotropic directions, which are used to develop a Continuum Damage Mechanics-based mesoscale model wherein constitutive laws are specifically formulated to reproduce NFC quasi-static response, including their highly nonlinear fibre-direction stiffness loss and inelasticity progression. Current progress of fatigue research is critically and extensively reviewed. Reported fatigue endurance and progressive damage behaviour of several NFC laminates are analysed. Existing knowledge on NFC fatigue damage is found to be insufficient and ambiguous, therefore inadequate for engineering design consideration. The unique fatigue-stiffening phenomenon reported for Flax-epoxy specimens is argued to be a misleading consequence of increasing strain-rate under constant stress-amplitude cycling. To minimise the influence of a varying strain-rate, original constant strain-amplitude fatigue tests are conducted on Flax-epoxy laminates, where no evidence of stiffening is observed. Considering this sensitivity to strain-rate, strain-amplitude controlled fatigue tests may be better suited for NFC investigation. Strain-controlled fatigue lives of Flax-epoxy can be modelled by a linearised strain/log-life relationship. Evolution of several material properties and dissipation phenomena (inelastic strain, peak stress, stiffness, hysteresis energy, superficial temperature) are measured, and correlated with SEM-observed damage mechanisms in the microstructure. An evolution/growth model is proposed to simulate laminate-scale stiffness degradation and cumulative inelastic strain as a function of applied peak strain and fatigue cycles, and is found to well-capture experimental trends for Flax-epoxy. The combined contribution of this work provides much-needed original data on the damaged-condition mechanical behaviour of Flax-epoxy and other NFCs under a variety of loading conditions, clarifies contradictory aspects of critical NFC behaviour, and proposes numerical methods to replicate observed progressive damage and failure in NFCs.


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