Frequency Effects on a Stiffness-Based Fatigue Failure Criterion in Flawed Composite Specimens

2009 ◽  
pp. 171-171-14 ◽  
Author(s):  
KL Reifsnider ◽  
WW Stinchcomb ◽  
TK O'Brien
Keyword(s):  
Fatigue Failure ◽  
Failure Criterion ◽  
Frequency Effects

A Note on the Shear Stress Criterion for Fatigue Failure under Combined Stress

1969 ◽  
Vol 20 (1) ◽  
pp. 57-60 ◽  
Author(s):  
R. E. Little
Keyword(s):  
Shear Stress ◽  
Fatigue Limit ◽  
Fatigue Failure ◽  
Failure Criterion ◽  
Basic Problem ◽  
Failure Criteria ◽  
Test Methods ◽  
Combined Stress ◽  
Stress Criterion

SummaryNishihara’s combined bending and torsion out-of-phase fatigue limit data are analysed. The Tresca shear stress failure criterion predicts strengths up to 30 per cent higher than observed. It thus appears that renewed attention should be given to the basic problem of developing reliable combined stress failure criteria. It is suggested that new test methods will be required for this purpose.

scholarly journals Investigation of creep and fatigue in high temperature polymer matrix composites using a micromechanical approach

2021 ◽  
Author(s):  
Alireza Sayyidmousavi
Keyword(s):  
High Temperature ◽  
Fatigue Failure ◽  
Polymer Matrix ◽  
Failure Criterion ◽  
Failure Modes ◽  
Polymer Matrix Composites ◽  
Matrix Composites ◽  
Difficult Situation ◽  
Strain Evolution ◽  
Micromechanical Approach

Polymer matrix composites (PMC’s) are widely used in critical aerospace structures due to their numerous advantageous mechanical properties. Recently, PMC’s have been considered for high temperature applications where viscoelasticity arising from the time dependent nature of the polymer matrix becomes an important consideration. This inherent viscoelasticity can significantly influence deformation, strength and failure response of these materials under different loading modes and environmental factors. With a potentially large number of plies of different fiber directions and perhaps material properties, determining a fatigue failure criterion of any degree of generality through experiments only, may seem to be an unrealistic task. This difficult situation may be mitigated through the development of suitable theoretical micro or macro mechanical models that are founded on considering the fatigue failure of the constituting laminas. The micro‐approach provides a detailed examination of the individual failure modes in each of the constituent materials i.e. fiber, matrix. In this work, a micromechanical approach is used to study the role of viscoelasticity on the fatigue behavior of polymer matrix composites. In particular, the study examines the interaction of fatigue and creep in polymer matrix composites. The matrix phase is modeled as a vicoelastic material using Schapery’s single integral constitutive equation. Taking viscoelsticity into account allows the study of creep strain evolution during the fatigue loading. The fatigue failure criterion is expressed in terms of the fatigue failure functions of the constituent materials. The micromechanical model is also used to calculate these fatigue failure functions from the knowledge of the S‐N diagrams of the composite material in longitudinal, transverse and shear loadings thus eliminating the need for any further experimentation. Unlike the previous works, the present study can distinguish between the strain evolution due to fatigue and creep. The results can clearly show the contribution made by the effect of viscoelasticity to the total strain evolution during the fatigue life of the specimen. Although the effect of viscoelsticity is found to increase with temperature, its contribution to strain development during fatigue is compromised by the shorter life of the specimen when compared to lower temperatures.

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