Abstract
In this paper, the fracture of notched polymeric specimens under compressive stresses was investigated both experimentally and theoretically. In the experimental section, to determine the load-carrying capacity (LCC) of U-notched specimens made of general-purpose polystyrene (GPPS) and polymethyl-methacrylate (PMMA) polymers, tests were performed on notched square samples under compression, i.e., negative mode I loading. In the observation of the nonlinear behavior of the two polymers in the standard compressive tests, for the first time, the equivalent material concept (EMC) was used under compressive loading to theoretically estimate the critical stresses of the two polymers, which were shown to be significantly different from the ultimate strengths obtained from the standard compression tests. By linking the EMC to the maximum tangential stress (MTS) and mean stress (MS) criteria, the LCC of the notched specimens was predicted. The outcomes are twofold: First, MTS, MS, EMC–MTS, and EMC–MS criteria provide accurate predictions of the experimental critical loads observed in the U-notched polymeric specimens; second, the combination of the EMC with the MTS and MS criteria, allow such predictions to be obtained without any need for experimental calibration.
Highlights
The presence of discontinuities such as cracks and notches in structures leads to stress concentrations that increase the risk of failure under different kinds of loading condition, and significantly reducing the corresponding structural strength
Original fracture tests were carried out on U-notched rectangular specimens made of PMMA and general-purpose polystyrene (GPPS) polymers under compressive loading
Experimental calibration methods based on the theory of critical distances (TCD) were implemented to obtain the critical stress and the critical distances of the maximum tangential stress (MTS) and the mean stress (MS) criteria
Summary
The presence of discontinuities such as cracks and notches in structures leads to stress concentrations that increase the risk of failure under different kinds of loading condition, and significantly reducing the corresponding structural strength. Most of the research dealing with the fracture of cracked or notched components has been performed under mode I and mixed mode I/II loading conditions, where fracture is caused by local tensile stresses. Under such conditions, physical aspects of failure are analogous between cracked and notched components, beyond the evident relaxation of the stress field when moving from cracked to notched conditions. Under compressive stresses, defects experience closing mode loading, known as negative mode I loading, and there is a greater difference between the behavior of components in cracked and notched conditions. In the case of notched components, the probability of contact between the notch faces is related to the distance between them, and a fracture may be expected because of damage nucleation and propagation from the notch tip
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