Utilizing the Anti-Plane Punch-Through Shear Specimen for Mixed-Mode I/III Fracture Analysis of Epoxy Resins

The primary objective of this study is to introduce and analyze a test geometry designed for measuring the shear fracture resistance of cracked epoxy resins under anti-plane loading conditions. This geometry is denoted as the anti-plane punch-through shear (APPTS) specimen. The APPTS specimen is a rectangular beam that has been weakened by two parallel pre-cracks separated by a specific longitudinal distance (S). This specimen is then subjected to anti-plane punch shear loads, commonly known as mode III loading. Initially, the APPTS specimen is modeled numerically using the contour integral method within the Abaqus code. This modeling approach helps to characterize the distribution of normalized stress intensity factors (SIFs) along the pre-crack front. The numerical simulations are conducted across a wide range of normalized pre-crack lengths relative to the specimen width (referred to as a/w), as well as normalized longitudinal distances (S) relative to the specimen length (referred to as S/L). The obtained results reveal that despite the application of an anti-plane shear load (mode III loading), the crack front of the APPTS specimen consistently experiences a combination of tensile stress (mode I) and anti-plane shear stress (mode III). This combination results in a negligible contribution of mode II stress in the crack front stress distribution. Furthermore, as the a/w ratio increases, there is a respectively a decrease and increase trend in the influence of modes I and mode III on the stress state of the crack front. In other words, by increasing the a/w ratio, the mode I stress does not reach zero, while mode III increases signifying the dominance of mode III loading. In addition to this, the ratio of normalized mode I to mode III SIFs indicates that when the S/L ratio is relatively low, the mode III stress state at the crack front becomes more dominant compared to the mode I stress state. In conclusion, the obtained normalized SIFs can be utilized as essential input parameters in theoretical criteria aimed at predicting the punching shear fracture envelope of cracked epoxy resin components during experimental tests.