Papers by Keyword: Notched Specimen

Abstract: Fracture mechanics has been a crucial aspect in the field of engineering science as technologies are rapidly growing nowadays. Various numerical methods have been developed to analyze fracture behaviour in different types of materials used in industries. Meanwhile, the application of polymers garners attention worldwide due to outstanding characteristics such as good strength, lightweight, and high temperature resistance, exemplified by polymers like polycarbonate (PC) and polypropylene (PP). Hence, failure aspects of such materials must be taken into consideration when conditions arise that may lead to failure, such as high-load impact, fatigue, and extreme temperatures. In this study, a bond-based Peridynamic model (PD) for the tensile behaviour, including fracture, of polymers has been developed. The PD model is constructed using the Centos software and encompasses both brittle and ductile fracture behaviours. Numerical results, including crack propagation, damage zone, and force-extension curves of notched specimens, are validated by comparison with experimental results of PC and PP. Through the validation process, PC specimens exhibit a difference percentage range for maximum load and rupture extension of 2.9% to 18.8% and 2.4% to 4.6%, respectively. PP specimens show a difference percentage range for maximum load and rupture extension of 31.2% to 43.5% and 0.9% to 30%, respectively. Consequently, the validation results indicate that the PD model for brittle specimens aligns more closely with experimental data compared to the PD model for ductile specimens.

Abstract: This paper presents the peridynamic (PD) numerical model for simulating a tensile test until total fracture for a brittle polymeric material namely polymethyl methacrylate (PMMA). U-notched and V-notched specimens were used to investigate the effect of the notches on the elongation and fracture of PMMA. The tensile elongation of PMMA exhibits nonlinearity with respect to the applied load, while the fracture occurs when the material stress has reached the ultimate tensile stress of the material. Similar elongation and fracture properties were applied on PD simulations. Two types of elongation equation are used namely brittle and ductile equations to form PD-brittle and PD-ductile models. The published experimental data of tensile fracture test on notched PMMA specimens are used as reference to validate the simulations of the PD models. The PD numerical force-extension curves have good quantitative similarity for V-notched specimen but adequate quantitative similarity for U-notched specimen. As for the quality of the fractured specimen shape, the PD simulations have good similarity for the V-notched specimen but adequate similarity for the U-notched specimen. The plot of the internal force distribution from the simulations of PD shows good qualitative similarity to the plot of the stress distribution from the published data of FEM in terms of stress concentration. From the PD results, it is observed that the PD-ductile model has better capability in producing accurate simulation of the notched specimens than the PD-brittle model.

Abstract: The paper presents the evaluation of limit deformations by the tensile test of notched specimens to measure the left side of forming limit curve. The notch radii R5, R10, R17.5 and R25 were machined on the specimens of 40 mm in width. The limit deformations have been assessed for Zn coated high strength steel TRIP with thickness 0.76 mm. Two types of deformation grid were electrochemically etched on the specimens: circles with diameter of 2 mm and the pattern of dots with diameter 0.5 mm and spacing 1 mm. The tensile test of notched specimens has been also numerically simulated. The experimentally measured limit curves have been compared to the mathematic Swift-Hill model.

Abstract: This article deals with multiaxial fatigue strength of notched round bars made of Cr-Al-Mo steel and tested under combined tension and torsion loading. Fatigue life is one of the important factors in design since majority of engineering components are subjected to variable loading. Most of mechanical components in engineering practice are subjected to combined loading, which can lead to sudden fatigue failure. In present work the fatigue life of specimens made of low-alloy Cr-Al-Mo high-strength steel is studied. Experiments were focused on the high-cycle fatigue region (over 100 000 cycles to final failure). The most relevant goal of this paper is to verify the efficiency of modified classical multiaxial fatigue criteria. The criterion proposed by Goncalves, Araujo and Mamiya was found to be the best in the fatigue life prediction for bending-torsion loading of notched specimens.

Abstract: Joining aluminium alloys with the use of welding techniques often impairs their strength properties and in some cases it is very difficult or even impossible. An alternative method for joining this type of material is friction welding including FSW welding. The airplane aluminium alloy 2024-T3 is an example of material that can be welded using this method. Heat emitted during the process, which contributes to the material plasticisation in the zones of welding, causes significant changes in the material structure, thus affecting the joint properties. Fatigue life calculations of this type of joint can be performed according to different approaches. One of them is a local approach which requires knowledge of local strains or stresses within the notch zone. This paper is a presentation of exemplary results of experimental and numerical tests of strain in the zone of notch that occur in a joint under time variable loading.

Abstract: The paper is focused on a numerical study of fracture test of quasi-brittle materials which is a combination of both the wedge splitting and the three-point bending configuration. Changes in some parameters of the test geometry lead to variations in constraint conditions at the crack tip, which affects the extent of the fracture process zone, i.e. the volume where the crucial processes, determining the possibility and extent of the failure take place. Differences indicated by the failure extents (expressed as the crack pattern) and stress distributions are plotted for several stages of loading for the proposed fracture test configurations.

Abstract: A research on the effect of strip defect in the notched specimen of low alloy hot rolled steel 16MnR at -196°C is carried out in this paper. 4-point positive and negative bending experiments of notched specimen with different preloads are carried out to introduce strip defects of different dimensions in the front of notch. And then the residual stress and work hardening is eliminated through high temperature tempering. Bending fracture experiment is carried out at -196°C. Through microscopic observation and the measurement and analysis of mechanical parameters, it is discovered that: when the preload ratio P0/Pgy0.861, the Pf /Pgy rapidly decreases as the P0/Pgy increases. That’s because the increase of local high stress-strain region caused by the strip defect at the front notch end makes the distribution of crack-shaped nucleus active region of cleavage fracture increase, causes the cleavage initiation and leads to discrete numeric values of material notch toughness Pf and W.

Abstract: This present contribution consists of implementing an advanced GTN damage model as a "User Material subroutine" in the Abaqus FE code. This damage model is based on specific nucleation and growth laws in order to predict the void coalescence properties of the material. When applied, this implementation predicts the damage evolution and the stress state of notched specimens made from dual phase steel. By comparing numerical predictions with experimental results, the numerical approach was improved and then validated.

Abstract: The cleavage fracture behaviors are studied in notched specimens of a low alloy hot rolled steel 16MnR. The results show that two types of cleavage initiation sites are existed in notched specimens, one being related to the inclusions ahead of notch root (IC type) and the other related to inclusions located ahead of string cracks far from the notch root (SIC type). The types of initiation sites are influenced strongly on temperature, changing from IC type at -196°C to SIC type at -130°C. In both IC and SIC initiation mechanisms, the crack nucleation is induced by inclusions and the final fracture is controlled by propagation of a ferrite grain-sized crack into matrix grain. The cleavage fracture of IC initiation type in notched specimens satisfies a dual-criterion model, i.e. a critical plastic strain ep ³e_pc for initiating a crack nucleus and a critical tensile stress syy³s_f for its propagation. While for SIC initiation type, the dual-criterion model is evolved with the expression of e_p+eps³e_pc and s_yy+syys³s_f.

Abstract: Giga-cycle fatigue behavior of notched specimens with stress concentration factor, Kt of 1.5, 2.0 and 2.5 for 0.65 mass% carbon matrix high speed steel, YXR3 with Rockwell C scale hardness number of 60.7 is investigated. The higher the stress concentration factor the lower the giga-cycle fatigue strength is. The emphasis is placed upon the subsurface crack initiation observed on all notched specimens. Crack initiation mode of high speed steel is discussed with respect to fracture surface morphology.