Strain Energy Diagram for Characterising Fatigue Behaviour in Structural Members and Machine Parts Subjected to Repeated Loads

2014 ◽  
pp. 107-123
Author(s):  
Zihai Shi ◽  
Yukari Nakamura ◽  
Masaaki Nakano
Keyword(s):  
Strain Energy ◽  
Fatigue Behaviour ◽  
Structural Members ◽  
Energy Diagram ◽  
Machine Parts ◽  
Repeated Loads

Fatigue accumulated damage in notched quasi-isotropic composites under high-temperature conditions: A discussion on the influence of matrix nature on the stress energy release rate

2017 ◽  
Vol 52 (17) ◽  
pp. 2397-2412 ◽  
Author(s):  
B Vieille
Keyword(s):  
Cyclic Loading ◽  
Energy Release Rate ◽  
Energy Release ◽  
Release Rate ◽  
Strain Energy ◽  
Strain Energy Release Rate ◽  
Strain Energy Release ◽  
Fatigue Behaviour ◽  
Polyphenylene Sulfide ◽  
Plastic Deformations

In order to investigate the contribution of matrix nature to the fatigue behaviour, the purpose of the present work is to establish the correlation between material toughness and macroscopic damage accumulation during tensile cyclic loading in the brittle (C/epoxy) and ductile (C/Polyphenylene sulfide) matrix systems. More specifically, this article presents a fracture mechanics-based approach to compute the strain energy release rate during fracture along with the macroscopic transverse crack growth in fatigue. The knowledge of energy-absorbing processes is important as they are responsible for the toughness of the composite. Woven-ply laminates are characterised by matrix-rich regions which may stop or slow down the growth of fatigue cracks by absorbing the mechanical energy through local plastic deformations at the cracks tip depending on matrix nature. With respect to C/epoxy laminates, the local plastic deformations at the cracks tip are prominent in highly ductile composite systems (e.g. C/Polyphenylene sulfide), and ultimately results in fatigue behaviour virtually independent of the applied stress level under high temperatures T > Tg. To evaluate the influence of matrix ductility and toughness on fatigue damage, a damage variable d based on the measurement of longitudinal stiffness at each cycle was used. A model derived from a Paris law and a fracture mechanics criterion were combined to: (i) evaluate the fatigue crack growth – (ii) compare the changes in the strain energy release rate G and the macroscopic damage d during cyclic loading. Macroscopic damage appears to be well correlated with the strain energy released during fracture.

scholarly journals Importance Assessment of Structural Members Based on Elastic-Plastic Strain Energy

2019 ◽  
Vol 2019 ◽  
pp. 1-17
Author(s):  
Yongjun Lin ◽  
Xianzhao Zhang ◽  
Wenqiang Xu ◽  
Meng Zhou
Keyword(s):  
Plastic Strain ◽  
Energy Method ◽  
Strain Energy ◽  
Plastic State ◽  
Displacement Curve ◽  
Structural Members ◽  
Elastic Plastic ◽  
Plastic Strain Energy ◽  
Importance Assessment ◽  
Strain Energy Method

Based on the elastic analysis, the existing methods of the importance assessment of structural members can only reflect the structural elastic behavior. To understand the plasticity and stiffness degradation of the structure, the present study proposes a member importance assessment method which takes the structural elastic-plastic strain energy or the generalized elastic-plastic strain energy as the performance parameter. First, the existing methods of member importance assessment are explained. Second, by pushover analysis, structural elastic-plastic strain energy is calculated in accordance with the story force-displacement curve, and structural generalized elastic-plastic strain energy is calculated according to the base shear-top displacement curve. Third, the importance of structural members is measured with its effect on the elastic-plastic strain energy or generalized elastic-plastic strain energy of the structure. Given the difference between structural performance parameters, the coefficient of member importance is defined. Finally, the importance of the masonry structure wall is quantitatively assessed using the elastic-plastic strain energy method, the generalized elastic-plastic strain energy method, the generalized stiffness method, and the ultimate bearing capacity method. Besides, the effect of the seismic fortification intensity and the number of structural stories on the wall importance assessment results is analyzed. According to the results, the elastic-plastic strain energy method and the generalized elastic-plastic strain energy method can both reveal the mechanical performance of elastic-plastic state of the structure under severe earthquake. Furthermore, the greater the seismic fortification intensity is, the more important the wall will be on the bottom floor, the more the total number of structural stories will be, and the more important the opening wall and its adjacent wall will be.

scholarly journals Strain energy-and stress-based approaches revisited in notch fatigue of ductile steels

2018 ◽  
Vol 165 ◽  
pp. 14009 ◽  
Author(s):  
Bruno Atzori ◽  
Mauro Ricotta ◽  
Giovanni Meneghetti
Keyword(s):  
Energy Density ◽  
Plastic Strain ◽  
Strain Energy Density ◽  
Elastic Strain ◽  
Strain Energy ◽  
Elastic Strain Energy ◽  
Fatigue Behaviour ◽  
Strength Reduction Factor ◽  
Plastic Strain Energy ◽  
Elastic Strain Energy Density

The constant amplitude, zero-mean stress, axial-fatigue behaviour of plain and bluntly notched AISI 304 L stainless steel specimens is investigated in terms of strain energy density. Concerning plain material, it was found that at the fatigue knee the plastic strain energy density is 1.49 times higher than the elastic strain energy density. In the authors’ opinion, the presence of plasticity at the fatigue knee is responsible for the unsuitableness of classical stress - based approaches to synthesise the fatigue behaviour of this material. On the contrary, the elastic-plastic strain energy density was found an efficient parameter to rationalise in a single scatter band fatigue data of plain and bluntly notched specimens. Based on this result, the classic stress-and the point stress-based approaches were revisited taking into account the presence of plasticity at the fatigue knee, by introducing an equivalent fully elastic material having a linear elastic strain energy density at the fatigue knee equal to that of the actual material. Accordingly, a coefficient of plasticity Kp was successfully introduced to modify the classical definition of fatigue strength reduction factor, Kf.

A Theoretical Study of Structural Disorder and Photoluminescence Linewidth in InGaAs/GaAs Self Assembled Quantum Dots

2001 ◽  
Vol 707 ◽  
Author(s):  
Yih-Yin Lin ◽  
Hongtao Jiang ◽  
Jasprit Singh
Keyword(s):  
Quantum Dots ◽  
Strain Energy ◽  
Minimum Energy ◽  
Structural Disorder ◽  
Energy Diagram ◽  
The Past ◽  
Configuration Energy ◽  
Structural Fluctuations ◽  
Self Assembled ◽  
Strain Tensors

ABSTRACTThe past few years have seen considerable efforts in growth and device application of self-assembled quantum dots. However, the photoluminescence (PL) linewidth, which represents structural fluctuations in dot sizes, is still in the range of 30-50 meV. This large linewidth has deleterious effects on devices such as lasers based on self-assembled dots. In this paper we will examine the configuration-energy diagram of self-assembled dots. Our formalism is based on: (1) an atomistic Monte Carlo method which allows us to find the minimum energy configuration and strain tensors as well as intermediate configurations of dots; (2) an 8-band k p method to calculate the electronic spectra. We present results on the strain energy per unit cell for various distributions of InAs/GaAs quantum dots and relate them to published experimental results. In particular we examine uncovered InAs/GaAs dots and show that in the uncovered state a well-defined minimum exists in the configuration energy plot. The minimum corresponds to the size that agrees well with experiments.

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