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Analysis of crack geometries on glass/polymer and polymer sandwich specimens
Abstract
Interfacial cracks in bimaterial and sandwich specimens in 4-point flexure were analyzed using the finite element method. The energy release rate(G) and the loading phase angle($\Psi$)were calculated in a variety of bimaterial and sandwich specimens. In the sandwich specimens, different crack configurations were analyzed. For sandwich specimens with fully formed cracks on both interface #s 1 and 2, the analysis predicted crack arrest on interface #1 and growth on interface #2. This phenomenon was observed in previous studies with glass/epoxy/glass sandwich specimens. The analysis also showed that the G value for the crack on interface #2 can be calculated by multiplying the G value for a crack on interface #1 by an appropriate correction factor. This correction factor depends on whether the precrack penetrated the epoxy layer or was arrested at interface #1. The loading phase angle for the crack on interface #2 was found to be greater when the precrack penetrated the intermediate layer than when it was arrested at interface #1. Subcritical crack growth and fracture energy(G$\sb{\rm c})$ measurements were made on glass/PMMA and glass/epoxy/PMMA specimens under high humidity. Threshold values for subcritical crack growth and G,values were lowest for the glass/PMMA interface and highest for the epoxy/PMMA interface with the precrack penetrating the epoxy layer. The Van der Waals bonds between glass and PMMA appear to be weaker than those between epoxy and PMMA. For a crack at the epoxy/PMMA interface in the glass/epoxy/PMMA sandwich specimen, threshold values for subcritical crack growth and G$\sb{\rm c}$ values were lower when the precrack was arrestedon interface #1 than when it penetrated the epoxy layer. The lower phase angle ($\Psi = 5\sp\circ)$ for the crack on interface #2 with the precrack arrested at interface #1 results in a large opening mode stress state on interface #2 which facilitates subcritical crack growth at lower threshold values and also lower G$\sb{\rm c}$ values as compared to the case when the precrack penetrates the epoxy layer and grows along interface #2($\Psi = 66\sp\circ).$
Subject Area
Mechanical engineering|Materials science
Recommended Citation
Prakash, Guru C, "Analysis of crack geometries on glass/polymer and polymer sandwich specimens" (1996). Doctoral Dissertations Available from Proquest. AAI9619424.
https://scholarworks.umass.edu/dissertations/AAI9619424