Papers by Keyword: Ductile Fracture

Abstract: Despite remarkable advances in additive manufacturing (AM), the uncertainty in direction-dependent strength and fracture behavior of metallic components still poses major challenges for their reliable structural application. The layered nature of laser powder bed fusion (LPBF) produces highly anisotropic textures and microstructure architectures that influence both plastic flow and fracture. While numerous studies have characterized tensile anisotropy, the coupling between build-induced anisotropy and stress-state-dependent fracture remains largely unresolved, yet it governs the structural integrity of AM parts under multi-axial loading. In particular, the extent to which anisotropy alters the ductile-to-brittle transition or fracture locus is still unknown. This study addresses this gap by combining experiments and advanced constitutive fracture modelling for two typical AM metals, austenitic 316L stainless steel and AlSi10Mg aluminum alloy. The goal is to formulate a unified, physically based description of anisotropic plasticity and fracture that is applicable across various material classes. LPBF samples of 316L stainless steel and AlSi10Mg were built at multiple orientations between 0° and 90° relative to the build direction. Uniaxial tensile tests were carried out with digital image correlation to capture full-field strain evolution and to determine r-values as a measure of plastic anisotropy. Complementary fracture tests under different stress states ranging from simple shear to plane strain tension were designed to evaluate the fracture dependence on stress states and anisotropy. It can be concluded that both alloys exhibit orientation-dependent flow and r-value during plastic deformation. The fracture strain decreases with rising triaxiality, yet its rate of decrease depends strongly on orientation, demonstrating a clear coupling between anisotropy and stress state.

Abstract: This work analyses the influence of batch-to-batch variability on both strain hardening and ductile fracture behaviour of a 42CrMoS4 steel under cold forging conditions. Mechanical testing combined with full-field strain measurements and finite element simulations is used to characterise material response and fracture under different stress states. Batch-dependent hardening laws are identified, and ductile fracture initiation is described using the Hosford–Coulomb criterion, calibrated independently for each material batch. The identified fracture strains and fracture surfaces exhibit a measurable variability between batches, even for similar stress-state conditions. The results provide quantitative evidence of batch-dependent material behaviour relevant for forming simulations

Abstract: In this regard, two beta titanium alloys in the Ti-Al-Mo-V-Cr system, Ti-3Al-5Mo-7V-3Cr (Ti-3573) and Ti-3Al-8Mo-7V-3Cr (Ti-3873), have been designed. Comparison of the microstructure and mechanical properties of both alloys after solution treatment was conducted. The result shows that the β grains in Ti-3873 alloy are abnormally grown at WQ. The elongation of Ti-3573 alloy is higher than that of Ti-3873 alloy, it is related to the the smaller grain size. The Ti-3873 alloy has moderate plasticity but higher yield strength and tensile strength. Fine and deep dimples associated with ductile fracture were obtained for the Ti-3573 alloy. The fractography of the β-substrate specimens showed that the fracture mode was ductile fracture. The Ti-3873 alloy has a combination of slip and twinning during deformation. It is possible for the Ti-3573 alloy to undergo both twinning and TRIP effect upon deformation. Therefore, Ti-3573 alloy exhibited good plasticity and strength matching.

Abstract: The paper extends Orowan’s method to the prediction of ductile fracture in plane strain rolling. In general, any uncoupled ductile fracture criterion can be used in conjunction with the solution found. However, the present paper focuses on a ductile fracture criterion based on the workability diagram. It is assumed that the initiation of fracture occurs at the axis of symmetry.

Abstract: This paper presents an efficient analytical method for design of streamline dies driven by fracture. The method is based on Bernoulli’s theorem relating pressure and velocity along any streamline extended to ideal flows in plasticity. The Cockroft-Latham criterion is adopted to predict the initiation of ductile fracture. In order to apply the method developed, it is not necessary to know the solution to the boundary value problem of plasticity. The final result is a simple relation between geometric parameters of the process and the constitutive parameter involved in the fracture criterion. Since the latter is supposed to be known for a given material, the relation determines a safe domain for drawing without fracture.

Abstract: In this study, the Drucker yield function and S-shaped strain hardening model are employed to describe the yielding and hardening behaviors of SUS304 respectively. An uncoupled ductile fracture criterion is calibrated and then utilized to construct the fracture locus of SUS304. To explore the effect of various notches on the prediction of ductile fracture, the constitutive models and ductile fracture criterion are then introduced into the ABAQUS/Explicit code to predict the onset of ductile fracture of various notched specimens. The comparison demonstrates that the ductile fracture criterion captures the fracture strains for all specimens with different notch radius accurately and the finite element models predict the strain distribution, strain evolution and load-stroke curves with good agreement for specimens with large notch radius compared with the experimental results.

Abstract: Pipeline transportation is the most economical and reasonable way to transport natural gas. However, there are still some technical problems in high grade gas pipeline, in which fracture control is one of the key problems. The ductile fracture for long-range expansion is the most destructive failure mode of high pressure gas pipeline. In this study, the determination and prediction methods of crack arrest toughness of high grade (X80 and above) pipe line steels were introduced. Their application range, advantages and disadvantages were analyzed. The results showed that the toughness of X80 pipe line steel can meet the needs of the pipeline crack arrest requirements. It is difficult for the ultra-high-grade (X90 and above) pipe line steel to arrest crack by their own toughness. Therefore, the crack arrester should be installed. This paper introduced the crack arrest principle, advantages and disadvantages of various kinds of crack arresters.

Abstract: The use of uncoupled damage models has been widely used over the years for the prediction of ductile fracture in engineering applications. Nevertheless, its applicability in the prediction of failure has been shown to be limited in the wide range of loading conditions encountered in different manufacturing processes. In order to enhance the formulation of former damage models, the Lode angle has been recently used to characterize the stress states along with the stress triaxiality. This new family of damage models has been demonstrated to give excellent results when proportional loading paths are considered, but its efficiency in more complex applications still need further analysis. To this end, a comparative study of former and recently developed uncoupled damage models is performed in this work. The identification of material parameters is done considering simple mechanical tests under different conditions. Then, the models are used to predict the onset and propagation of cracks during blanking, where numerical predictions are compared with experimental results. Finally, the selected damage models presented a remarkable overall performance in the range of clearances under study.

Abstract: Variety of metals are complex materials exhibiting various behavior under different loading. Many metallic materials exhibit Tresca-like behavior rather than von Mises. It means different behavior in tension under plane strain and uniaxial stress conditions. This might be described by Lode dependent plasticity which should result in better prediction in force or torque responses of material tests. Good agreement between computation and experiment is also very important when calibrating the ductile fracture criteria. Several tests under plane strain and uniaxial stress states were carried out on aluminum alloy 2024-T351 where the Lode dependency was significant. The Lode dependent plasticity was implemented along with von Mises and Tresca-like yield criteria, which resulted in improvement of force–displacement responses of plane strain tests simulations. But it also caused significant change in the stress state of tensile flat and grooved plates which wrongly approached uniaxial tension condition. This inconvenience prevents plane strain experiments from using for calibration of ductile fracture criteria under these circumstances.

Abstract: The theory of sheet and bulk ideal plastic flows is used for the preliminary design of metal forming processes. The present paper develops an approach to incorporate the Cockroft and Latham ductile fracture criterion in this design method for stationary bulk flows. In particular, it is demonstrated that the initiation of ductile fracture can be predicted without having the ideal flow solution for stress and strain in the plastic zone (it is only necessary to know that the solution exists). Using the approach proposed the initiation of ductile fracture in axisymmetric drawing is predicted.