Papers by Keyword: Fracture

Abstract: Medium-Mn steel (MMnS) and quenching and partitioning (QP) steels are two representatives of third-generation advanced high-strength steels (3^rd Gen AHSS), developed to achieve an optimal balance between strength and ductility. In forming applications, global formability reflects a material’s resistance to necking, while local formability indicates its resistance to fracture. Both aspects are essential for assessing mechanical performance. Global formability is often characterized by the forming limit curves at necking and is highly sensitive to work hardening behavior. Similarly, the forming limit curves at fracture determined from different stress states can be applied to evaluate the local formability. In addition, these deformation characteristics can be influenced by anisotropy introduced during sheet processing. Rolling process introduces orientation-dependent variations in both plastic flow and fracture behavior, which significantly affect necking development and fracture initiation. This study investigates and compares the global and local formability of various 3^rd Gen AHSS grades, with a focus on the influence of anisotropy. To investigate the anisotropic effects on plasticity and ductile fracture under different stress states, tensile tests were conducted on specimens with various geometries and orientations cut from sheet materials. Based on the tensile tests, the forming limit framework of Shen et al [1] was broadened to include anisotropic effects.

Abstract: The influence of the stress state on damage evolution, fracture behavior, and component performance is well established for proportional loading conditions. In contrast, many industrial sheet-forming processes involve non-proportional loading paths, which can significantly alter material hardening and fracture responses. Recent results have shown, that load direction changes affect damage evolution in the dual-phase steel DP800. This paper aims to investigate to what extend these results can be transferred to the aluminum alloy AA6082-T6. Therefore, specimens are first prestrained in uniaxial tension and subsequently reloaded either in the same direction or orthogonally, using additional tensile tests. Fracture strains during the subsequent tensile tests are determined by Aramis DIC. Orthogonal load direction changes lead to an increased fracture strain for DP800, but decreased fracture strain for AA6082. While the observed behavior of DP800 can be attributed to the void morphology, which is established during prestraining, the results of AA6082 indicate different damage mechanisms which cause this behavior.

Abstract: The aim of the study was to prepare samples suitable for testing the shape memory phenomenon in ceramic systems. Testing would be carried out by preparing micro-objects with dimensions in the order of micrometers using SEM/FIB techniques, and subsequent testing using a nanoindenter. The article deals with the influence of the preparation method on the properties of samples prepared by conventional annealing and spark plasma sintering. Two commercial powders were used, namely PSZ-10C and PSZ-20C. The microstructure of the samples, fracture surfaces and HV hardness, as well as indentation hardness were evaluated on the prepared samples. It was shown, that both conventional annealing and SPS can be used for preparation of samples with a suitable grain size, but also that the preparation method has a significant impact on the properties of the sample. Depending on the preparation method, the grain size varied from approximately 1 μm to 50 μm. There is also difference in the character of the fracture surfaces and in the hardness of the samples, where a difference in indentation hardness from approximately 10 GPa to approximately 20 GPa was measured.

Abstract: Fatigue damage is one of the key degradation mechanisms affecting the service life and reliability of aluminum alloys in a wide range of technical applications. The present study focuses on the fracture mechanisms of aluminum alloys under cyclic loading, with a view to the initiation and analysis of fatigue crack propagation in the context of the microstructural characteristics of the material. Special attention was paid to the influence of grain morphology, distribution and type of intermetallic phases, as well as the presence of casting defects on the initiation and development of cracks. Fatigue experiments were performed on a selected Al-Mg alloy of the EN AC 51200 type for the use of three-point bending loading. The results show that the key factors affecting the fatigue behavior are the size and distribution of precipitates, the nature of the interfaces between the phases and the occurrence of microcracks initiated mainly in areas of stress concentration. The knowledge gained contributes to a deeper understanding of fatigue mechanisms in aluminum alloys and provides a basis for their optimization in terms of composition and technological processing in order to increase their resistance to fatigue failures.

Abstract: Modern pipeline steel has high toughness and ductility, which can effectively prevent long-distance crack propagation. The full-scale blasting test is the most effective method to verify and evaluate the crack propagation and arrest behavior in high-grade pipeline steel pipes. This article investigates the crack propagation and crack arrest behavior of X90 grade natural gas pipeline steel pipes through full-scale blasting tests. The test results show that once the X90 grade natural gas pipeline steel pipe cracks and propagation under a pressure of 12MPa, as long as the Charpy impact toughness CVN of the steel pipe is greater than 286J, it can ensure effective crack arrest of the pipeline, providing technical support for the application of X90 high-grade pipeline steel pipe in high-pressure transmission pipelines.

Abstract: Microforming holds great importance due to the rising demand for miniaturized parts across diverse industries. It enables the efficient mass production of small-scale components using sheet metals. By exploring microforming processes, researchers can uncover the unique challenges and opportunities associated with manufacturing at the microscale. This research work investigates the impact of temperatures during the annealing on the mechanical properties, microstructural behaviour and formability of austenitic stainless steel 316 thin sheets. The thin sheet, with a thickness of 50µm was considered for the present analysis and were annealed at temperatures ranging from 400 to 1000°C for 30 minutes. Tensile tests were performed and mechanical properties were evaluated at various annealing temperatures. It was witnessed that as the temperature of annealing increases, the ultimate tensile strength reduces and ductility enhances. Erichsen cupping tests were conducted to assess the formability, measuring the dome height of the drawn cups. The results revealed that the as-received thin sheet exhibited poor formability. However, increasing the annealing temperature resulted in enhancing the formability, as evidenced by an increase in the dome height of the drawn cups. Furthermore, the annealing process led to an increase in grain size, which in turn inversely affected the material strength. Therefore, annealing not only enhanced formability but also influenced the microstructural characteristics of the stainless steel 316 foils. Fractography studies were done and the results show that higher annealing temperatures result in ductile fracture, which is favorable for practical applications. At lower temperatures, brittle fracture occurs with the presence of river markings. The present work helps in selecting appropriate annealing conditions for improved toughness and resistance to sudden failure in micro parts.

Abstract: Carbon and glass fabric reinforced polymer (C/GFRP) composites are extensively used in aerospace and sports industry because of their exceptional properties. However, during service, static and dynamic bending loads can ensue damage in composites affecting their strength, stiffness and energy absorption. Carbon fiber composites, being inherently brittle, are prone to sudden catastrophic fracture without ductile-like behavior of metals. This study investigates mechanical behavior and damage mechanisms of woven C/GFRP composites in on- and off-axis orientations during bending. Initially, bending tests with quasi-static loading were performed, followed by dynamic ones using an Izod impact testing apparatus. Results showed distinct behavior in on-axis CFRP laminates with brittle fracture. Off-axis CFRP samples and both on- and off-axis GFRP laminates showed signs of damage and non-linear behavior, yet they retained their ability to bear loads. Significantly, off-axis specimens of both types and on-axis GFRP laminates exhibited enhanced energy absorption capabilities without experiencing fracture, undergoing pseudo-ductile deformation. CFRP specimens were analyzed with micro-computed tomography (micro-CT), provided insights into prevalent damage modes such as matrix mircocracking, debonding of tows, delamination and breakage of fabric. While on-axis CFRP laminates experienced brittle fracture, off-axis specimens exhibited a ductile-like response attributed to matrix plasticity, cracking and fiber trellising before eventual failure.

Abstract: In this work, rectangular sheets of composite materials consisting of epoxy with a single layer of fiberglass were studied with the internal crack at angles (0°, 90°) with the x-axis in the presence of nanomaterial TiO₂ in proportions (1 wt%, 2 wt%, and 3 wt%), the study was experimental and numerical using the ANSYS. The sample mold was made from plastic using a CNC machine. One case was studied in both the experimental and numerical parts, which is clamped-clamped-free-free (CC-FF). After conducting the test, it was found that the crack negatively affects the rectangular composite plate, as it reduces the value of the natural frequency and increases the value of damping. However, in the case of adding the nanomaterial, it was found that the natural frequency increases with the increase in the percentage of nanomaterials, and the maximum value of the natural frequency was at 3% because it works to increase hardness rectangular plate stiffens and reduces damping. The error rate between the experimental and numerical parts did not exceed (9.717%).

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 integrated two severe plastic deformation methods, namely frictional extrusion, and friction stir spot welding to obtain synergetic benefits and create a friction extrusion spot welding (FESW) process. The FESW process was carried out with the use of AA1xxx Al alloy by interchanging the location of the predrilled extrusion hole (between the upper and bottom plates). The microstructure, tensile-shear load, and fracture behaviours of the welds were investigated. The results revealed the presence of no weld discontinuities/flow-aided defects while the FESW process was effective in filling the extrusion holes irrespective of the location of the predrilled holes. An inverse relationship was found to ensue between the tool’s rotating speed and the tensile-shear load of the bottom plate hole-friction extrusion spot welded joint joints while a direct correlation occurred between the tensile-shear load and the rotational speed (up to 1100 rpm) in the top plate hole-friction extrusion spot welded joints. The difference in the tensile and fracture behaviours of the two weld categories is attributed to the disparity in the hole-filling mechanisms. The maximum tensile shear load of 3.1 kN (at 710 rpm) and 3.3 kN (at 1100 rpm) were obtained in the bottom plate hole-and top plate hole-FESW joints respectively.