Recent studies on the mechanics of materials have shown that the ductile fracture is significantly affected by the stress invariants among progressive plastic deformation. In this paper the micro-mechanical Gurson-Tvergaard-Needleman (GTN) model is utilized to investigate the fracture behavior of high-strength steel AISI 4340 under various stress triaxialities. Experimental tensile tests were conducted on the smooth and notched round-bar specimens to evaluate the e ect of the stress triaxiality on the fracture initiation. Subsequently, finite element (FE) simulations were implemented using Abaqus/Explicit via the user subroutine VUMAT. The comparison between the simulations and experimental results indicate the best accuracy of the GTN micromechanical model to appraise the ductile fracture initiation. Furthermore, the results demonstrate the significant effect of the stress triaxiality value on the start of the ductile rupture.

In Brief Gestational trophoblastic neoplasia (GTN) refers to a group of malignant neoplasms that consist of abnormal proliferation of trophoblastic tissue and may follow a hydatidiform mole or a non-molar pregnancy. Despite their malignant nature, these neoplasms are curable, especially in the low-risk group. Patients with low-risk GTN have an overall excellent prognosis with survival rates of 100 percent after treatment using six cycles of methotrexate or actinomycin injection on average (1, 2). Second curettage may be considered an alternative therapeutic method to reduce the burden of chemotherapy or the length of medication (3) and many oncologists tend to try this intervention instead of chemotherapy, especially in patients who presented with vaginal bleeding and retained products of conception. Due to the low incidence of GTN, the design of a standard, a single-center comparative study between treatment methods looks problematic...

In this paper the capability of Gurson-Tvergaard-Needleman (GTN) model in the prediction of ductile damage in 7075-T651 aluminum alloy is investigated. For this purpose, three types of specimens were tested: Standard tensile bars, Round notched bar (RNB) specimens and compact tension (C(T)) specimens. Standard tensile bar tests were used to obtain the mechanical properties of the material and to calibrate the independent parameters of GTN model. RNB and C(T) specimen test results were used for validation of the calibrated parameters. Finite element analyses were carried out using ABAQUS commercial software for two purposes, calibration of the GTN model parameters and validation of the model predictions. The comparison between the finite element analyses and the test results suggested that the GTN model is capable of damage prediction in notched specimens, but not a good in cracked specimens. Finally, To show the applicability of the model in industry-level problems, the model is used for damage predictions of internal pressure vessels made of 7075-t651 aluminum alloy.

This study investigates the effect of material parameters of the Gurson-Tvergaard-Needleman (GTN) model on the failure prediction of cellular structures. The effect of elastic modulus, calibration parameter of GTN model, isotropic hardening, fracture strain, and strut diameter on the load-displacement curve of a lattice structure fabricated by Selective Laser Melting (SLM) has been studied by using the finite element method. The power law of Hollomon has been used to model the isotropic hardening behavior. The considered lattice structure is made of AlSi10Mg alloy, which is used in different industries. A 20cm×20cm×20cm structure with 4 Body Centered Cubic (BCC) unit cells in x, y, and z directions have been considered. The results show that 250000 elements for one-quarter of the lattice structure are quite enough to obtain acceptable results. The effect of prescribed parameters on the load-displacement curve of the lattice structure has been studied. Based on the obtained results, diameter and hardening behavior are the most influential parameters and the significant effect on load-displacement curve has been observed.