Long-term failure of transversely loaded glass/iPP

Herein, temperature‐dependent long‐term behavior of polypropylene and its transversely loaded unidirectional glass fiber reinforced composite is investigated and a lifetime prediction method is proposed, which is based on the observed long‐term failure mechanisms. Furthermore, the effect of cooling rate during processing on the time‐dependent behavior is addressed. The composite is revealed to exhibit multiple molecular deformation mechanisms, similar to neat polypropylene, which is modeled using the Ree–Eyring approach. Failure kinetics under constant‐strain‐rate and creep tests are found to be identical and switching from creep to cyclic loading decelerates the failure, which are signs of plasticity‐controlled failure. Hence, lifetime is predicted well by using a lifetime prediction methodology for the plasticity‐controlled failure which combines the Ree–Eyring approach and the concept of critical strain. A change in the cooling rate alters the deformation and failure kinetics: lower cooling rates promote embrittlement

Total fatigue life estimation of aircraft structural components under general load spectra

This work presents total fatigue life prediction methodology of aircraft structural components under general load spectrum. Here is presented an effective computation procedure, that combines the finite element method (FEM) and strain-life methods to predict fatigue crack initiation life and fatigue crack growth model based on the strain energy density (SED) method. To validate computation procedure in this paper has been experimental tested specimens with a central hole under load spectrum in form of blocks. Total fatigue life of these specimens, defined as sum of crack initiation and crack growth life, was experimentally determined. Crack initiation life was computed using the theory of low cycle fatigue. Computation of crack initiation life was realized using Palmgreen-Miner’s linear rule of damage accumulation, applied on Morrow’s curves of low cycle fatigue. Crack growth life was computed using strain energy density (SED) method. The same low cyclic material properties of quenched and tempered steel 13H11N2V2MF, used for crack initiation life computation, were used for crack growth life computation. Residual life estimation of cracked duraluminum aircraft wing skin/plate 2219-T851 under multiple overload/underload load spectrum was considered too. Presented computation results were compared with own and available experimentally obtained results