Experimental results of fatigue testing for calibration and validation of composite progressive damage analysis methods

Abstract

The Air Force Research Laboratory led a research effort to benchmark the accuracy of static and fatigue predictions of several emerging composite progressive damage analysis techniques. The static portion of this technical effort is described in detail in a previous special issue of the Journal of Composite Materials. This paper provides the details of the fatigue experiments that were conducted to calibrate and validate the computational models. Initially, in-plane and out-of-plane S–N curves were generated through coupon tests that were performed on unidirectional laminae. The challenges experienced during fatigue testing of in-plane, matrix-dominated unidirectional coupon specimens are presented in detail. The higher fidelity test data from the fiber-dominated and out-of-plane experiments are also included in this paper. Following the calibration experiments, a series of tension–tension fatigue validation tests were conducted on open-hole coupons with three different stacking sequences. Each specimen was cycled to a pre-determined number of fatigue cycles, followed by static residual strength tests in both tension and compression. This paper provides the stress–strain responses of these validation tests as well as high-resolution X-ray computed tomography images of the subsurface damage as a function of cycles. Seven analysis teams used these test results to calibrate their models and to benchmark the accuracy of their predictions of damage and residual mechanical properties.

Fatigue characterization study of CFRP under hygrothermal environment based on continuum damage mechanics model

“…Besides, we can conclude the following: The fatigue damage process of the composite can be divided into three stages: the damage accumulates rapidly in the first stage because microcracks increase and some fibres with low strength break; the second stage shows a slow and stable fatigue damage growth; and in the final stage, the fatigue damage increases rapidly once again before the complete failure of specimens. Such a damage evolution conforms to the damage accumulation characteristics of general composites 32 Parameter m 1 is always less than 1 while parameter m 2 is more than 1 all the time.…”

Micromechanical analysis of longitudinal and shear strength of composite laminae

“…Some references employed the two strengths defined by the standards, instead the only rupture shear strength as the most common procedure. 37 For instance, Jumahat et al. 38 reported offset strength equal to 52 MPa and rupture strength equal to 101 MPa for carbon fiber composite, while Laustsen et al.…”

Progressive failure simulation in laminated composites under fatigue loading by using discrete damage modeling

“…A detailed description of the experimental procedures for obtaining these properties is presented in Clay and Knoth. 15 The properties are listed in Table 3. In the fatigue section of the exercise the only difference between the blind and the corrected predictions was correcting an algorithmic error, which went unnoticed in the method validation on 2D examples.…”

“…13,14 The second phase, which is the subject of present paper, consisted of predicting the fatigue performance of OH laminates. 15,16 Three different layups were subjected to specified number of fatigue loading cycles and then tested for residual static strength in tension and compression. In addition, stiffness degradation as a function of fatigue cycles was predicted and compared to experimental data.…”