Ali Reza Torabi

Material extrusion (MEX) is an extensively used additive manufacturing technique that facilitates the fabrication of precise physical components with complex geometries through successive material deposition. However, the anisotropic behavior inherent to MEX-printed materials can substantially influence their fracture response. This study examines the fracture behavior of U- and blunt V-notched (BV-notched) MEX-printed Acrylonitrile Butadiene Styrene (ABS) under symmetrical three-point bending using rectangular specimens with a symmetrical [0/90]_s cross-ply printing architecture. To this end, three different notch root radii within the 1–4 mm range are experimentally investigated, and the measured fracture loads are compared with theoretical-numerical predictions obtained by integrating the virtual isotropic material concept (VIMC) with four failure models, namely the point stress (PS), mean stress (MS), and averaged strain energy density (ASED) criteria, as well as the extended finite element method coupled with a cohesive zone model (XFEM-CZM). All four VIMC-based criteria provide reasonable correspondence with the experimental results. Among them, the ASED-VIMC criterion exhibits the lowest average percentage difference of 5.7% for the 1–4 mm range of notch root radius, symmetrical [0/90]_s cross-ply printing architecture, and symmetrical three-point bending, followed by the PS-VIMC criterion with 7.4%. ASED-VIMC criterion also demonstrates the most consistent performance for both notch configurations, likely due to its lower sensitivity to notch geometry.

Purpose: This study aims to investigate the effect of specimen size on the fracture resistance of V-notches with end holes (VO-notched) polymeric samples under opening mode loading experimentally and theoretically. Design/methodology/approach: First, a number of VO notched Brazilain disk (VONBD) and VO notcehd semi-circular bend (VONSCB) samples with different sizes were made from polymethyl methacrylate and general-purpose polystyrene sheets and then were tested under pure Mode I loading. After that, it is tried to predict the fracture resistance of notched samples using two stress-based criteria [point stress (PS) and mean stress (MS)] considering the size effect. Findings: First, it is found from experiments that the fracture resistance of polymeric VO-notched specimens varies with the size of specimen in such a way that notch fracture toughness increases by increasing the specimen size. Secondly, it is found that the PS and MS criteria are able to predict in good accuracy the fracture resistance of tested samples. Originality/value: The size effect on the notch fracture toughness of VO-notched polymeric samples is investigated for the first time, and it is the main novelty of this research.

In this research, the cohesive length of various rock types is measured using quantitative fractography alongside a recently developed multifractal analysis. This length is then utilized to gauge material cohesive stress through the theory of critical distances. Furthermore, the fracture process zone length of different rings sourced from identical rocks is assessed as a function of ring dimensions and experimental measurements of fracture toughness, in accordance with the energy criterion of the finite fracture mechanics theory. Subsequently, employing the stress criterion within coupled finite fracture mechanics, the failure stress corresponding to the fracture process zone is determined for various rings. Ultimately, through interpolation, the critical stress corresponding to the cohesive length, quantified via quantitative fractography, is approximated. Remarkably, the cohesive stress values derived from both methodologies exhibit perfect alignment, indicating the successful determination of cohesive length for the analyzed rock materials. The study also delves into the significant implications of these findings, including the quantification of intrinsic tensile strength in quasi-brittle materials and the understanding of tensile strength variations under diverse stress concentrations and loading conditions.

The purpose of this study is to predict the load-bearing capacity (LBC) of fracture specimens containing V-notched friction-stir welded (FSWed) joints of AA7075-Cu and AA7075-AA6061 materials and subjected to mode I loading conditions. Due to the resulting elastic-plastic behavior and the corresponding development of significant plastic deformations, the fracture analysis of the FSWed alloys requires elastic-plastic fracture criteria, which are complex and time-consuming. Thus, in this study, the equivalent material concept (EMC) is applied, equating the actual AA7075-AA6061 and AA7075-Cu materials to equivalent virtual brittle materials. Then, two brittle fracture criteria, the maximum tangential stress (MTS) and mean stress (MS), are utilized to estimate the LBC of the V-notched FSWed parts. The comparison between the experimental results and the theoretical predictions reveals that both fracture criteria, in combination with EMC, can accurately predict the LBC in the analyzed components.