Abstract
Recent studies on local stress fields in proximity of crack and notch tips have shown that Strain Energy Density (SED), averaged in a circular control volume surrounding the point of stress singularities, represents a reliable engineering approach for assessing the brittle fracture of several brittle materials. It is worthy of notice that the application of SED criterion and the reliability of its results are strictly related to the proper determination of fracture parameters, i.e. the critical value of deformation energy Wc and the radius Rc of the control volume. This work presents an experimental methodology for their determination by means of notched specimens for different polyurethane densities, ranging from 100 to 651 kg/m3. Then, once obtained these critical parameters, the failure load in different types of notches and cracked specimens under mode I have been predicted. Moreover, for cracked specimens under mixed mode and mode II, the authors propose a personal approach that confirms PUR foams can be treated as brittle materials
Highlights
I n the last years, Polyurethane (PUR) has widely gained interest in industrial applications because of its high versatility
Their mechanical properties have been extensively investigated in the past, showing a relationship, based on the geometry of cellular structure and the relative density, with solid materials used for manufacturing [2,3], and revealing a crushable behaviour in compression, characterized by the capability to absorb considerable amount of energy due to plateau and densification regions
In a research by Negru et al (2015) it’s defined the inherent stress for the Theory of Critical Distance (TCD), an approach based on the same theory of strain energy based (SED) method, they belong to the linear elastic mechanic fracture theory (LEFM)
Summary
I n the last years, Polyurethane (PUR) has widely gained interest in industrial applications because of its high versatility. The criterion states that brittle fracture failures occur when the strain energy density averaged in a circular control volume of radius Rc, which surrounds a crack or notch tip, reaches a critical value Wc dependent on the material. The robustness of this criterion has been proved by several works on different notches geometries and on different loading conditions [21,22,23,24,25,26,27]. The main purpose of this work is to evaluate the effectiveness of SED criterion on PUR foams, aiming to experimentally evaluate the main parameters of this method, i.e. Rc and Wc
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