Papers by Keyword: Failure

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 article summarizes the results of comprehensive theoretical and experimental studies of ice fracture under shock and explosive loads. Artificial ice and freshwater river ice were considered as objects of research. The results of full-scale underwater explosive tests are presented. Post-explosion analysis of the crushing of a 130-day ice sheet, including the morphology of destruction and diameter and state of the ice edge were obtained. The results of a five-layer ice target impacted by a low-velocity striker showed that a brittle fracture mechanism was dominant. A phenomenological model of ice destruction is briefly described. The model was a complex one of continuum mechanics and was based on fundamental conservation laws. The ice failure concept was based on a deterministic approach and the combined use of several failure criteria. The finite-element Lagrangian method contained a new method for isolating the discontinuity surfaces of materials. The calculations were carried out using the noncommercial software package Udar.Os.1. The impact of an ice cylinder on a rigid wall (aluminum plate) was simulated. Good agreement was obtained in terms of the morphology of the fracture and the velocity of the fracture wave. The contact surface algorithm was illustrated, which helped save computational time when modeling some problems of perforation and penetration, including the detonation process. In the numerical experiment, ice without phase transitions with averaged mechanical properties was considered. The impact response of the ice blocks to the shock and explosive load was simulated. The perforation of structures consisting of ice cubes and thin steel plates above and on them is simulated. Deep penetration of the steel sphere into an ice block and an ice block protected by a metal plate was simulated. Using numerical modeling, the location of explosive substances for the most effective fracture of thick ice was determined.

Abstract: The aim of the work was to assess the nature and causes of defects – cracks in the welds of membrane wall panel tubes (MW) of a thermal power plant boiler made of T24 steel. This steel is intended to produce MW evaporators and superheaters for power plant units operating in the area of supercritical steam conditions. Its advantage, compared to the originally used materials, is higher creep resistance. The main expected advantage of the steel was to obtain optimal properties of welded joints without subsequent post-weld heat treatment (PWHT).

Abstract: Studying of the strength characteristics of polymer composite materials, which are used in the structures for various applications, is an important subject for research. Here one of the major issues is the development of fastening techniques to maximize the strength characteristics of composite fibers. Based on the modification of the available test methods, a set of specimens and devices has been developed to determine the shearing (cut) strength from the fastener hole to the edge of the composite part. For this purpose, we used the modified specimen sequentially shearing along the contour after each test cycle in order to find the required parameter depending on the distance from the fastener to the part edge. According to the result of experimental studies, possible types of shearing test and shear test failures were identified. It is demonstrated that shearing strength and shear strength in the specimen plane are different characteristics with no correlation between them. It is found that a shearing in the classic sense is observed only for high-anisotropy structures when they are loaded in the more rigid direction, whereas the complex modes of failure occur for the heavily reinforced composites used. For example, during testing a pure shearing was observed in 0° planes in the specimens with the package structure of [0^°_0.7; ±45^°_0.2; 90^°_0.1], while it was observed both for the holes drilled in 0° and 22.5° directions in the specimen with the structure of [0^°_0.8; ±45^°_0.2]. We obtained the quadratic engineering dependence to predict shearing strength of the heavily reinforced basic composite. Based on processing of the experimental results, a recommendation has been made on the need for constant experimental support of the design process, which can be implemented by the proposed specimen and testing device.

Abstract: Due to the complex compression failure process of fiber composite materials, especially the direct bearing situation of the composite material end face, it is quite difficult to accurately predict it. At present, the design of composite material compression performance mainly considers a large safety factor, and a compression failure assessment method that can meet the needs of reliable engineering applications is still a challenge and a key issue that the engineering community urgently needs to solve. This article reviews the widely studied shear type buckling model, extensional type buckling model, matrix strain failure theoretical model, matrix shear failure theoretical model, interlayer shear failure theoretical model, elastic micro buckling model, plastic micro buckling model, three parameter model, fiber microbuckling finite element model and ply mesobuckling finite element model of fiber reinforced composite materials that have been publicly published in recent years, which were analyzed and summarized, providing reference for further in-depth research in the future.

Abstract: Anisotropic conductive film (ACF) is frequently used in the packaging manufacture for fine-pitch conductivity and interconnection, maintaining the electrical and mechanical connections between micro-electrodes. A key determinant of good conductivity is the deformation, fatigue, and breakage of conductive particles within the ACF packaging. This study aims to measure the resistance changes of specific conductive channels and observe the microscopic fatigue damage of compressed ACF conductive particles through the fabrication of Flex Printed Circuits (FPC) / Indium Tin Oxide-coated Polycarbonate (ITO-coated PC) specimens and the setup of bending experiments. The results show that the deformation, fatigue, and breakage of conductive particles will quantitatively affect electrical conductivity performance. By microscopically observing the breakage morphology of conductive particles before and after bending, it can be found that bending in the ACF packaging area further exacerbates the previously compressed and broken conductive particles, with cracks continuing to grow and shatter.

Abstract: This paper involves a fundamental study of a numerical method for progressive collapse resistance design of floor-to-floor joints in precast cross-wall structures. It presents a 3D numerical study of a floor-to-floor system with longitudinal and transverse ties. The model is also used to derive the post-bond behavior and the mechanism of forming catenary action concerning the bond behavior in precast cross-wall structures. The obtained results indicated the adequacy and applicability of the code specifications in British Standard, Euro Codes, and DoD 2013. Discrepancies in the tie-force between the numerical results and codified specifications have suggested an inappropriate use of the current TF method, hence, an improved model based on the numerical results has been proposed to address this concern. To the authors’ best knowledge, this is the first numerical study to investigate the behavior of floor-to-floor joints following the removal of wall support in typical precast cross-wall structures when considering bar fracture and pull-out failure mode..

Abstract: The wear failure is widely found in steel bars used for coal screener machines in the mining industries. The failed parts of such components require immediate replacement to lengthen the machine's service life. This work aimed to investigate the structure and properties of the worn bar of a screener machine after experiencing wear failure and analyze the wear mechanism. The work started by machining the sample from the original bar, then grinding and polishing. The microstructure of the worn samples was observed using SEM and XRD. The hardness distribution of the bar was measured from the periphery to the core. The results of this work would provide evidence of wear sources responsible for the wear failure.

Abstract: This article presents an experimental research carried out on polymer sheet deformed by conventional forming, i.e. tensile and Nakajima tests, as well as by single point incremental forming (SPIF). The analysis is performed for polycarbonate (PC) polymer sheet material within the framework developed in previous recent papers of the authors, which the aim of defining a complete testing methodology for assessing formability and failure by necking and fracture of polymeric sheets. In the case of SPIF, truncated pyramid and cone test geometries are selected, enabling a variety of strain states from plane to biaxial strains. The results obtained allow an accurate evaluation and assessment of the forming limits by necking and fracture within the material forming limit diagram (FLD), and also include an analysis of the influence of the process parameters on the formability and failure modes attained in the case of incremental forming.

Abstract: Deterioration of metals and alloys due to corrosion has been observed to be a serious challenge in coastal or marine environments. Exposure of mild steel to marine environments often results into dilapidation of physical structure over time. This study addresses the quick response of mild steel failure using NiZnP modified Al₂O₃ functional composite by electrolytic process. The deposition was done with stable pH of 4.5, heated bath temperature of 95°C, stirring rate of 200 rpm and deposition time of 20 min. The materials chemistry of the developed alloy was examined using open circuit potential and linear polarization technique. The structural mechanism and crystal phase formation was characterized using scanning electron microscope (SEM) equipped with energy dispersive spectrometer (EDS) and X-ray diffraction analyzer. The corrosion results under 3.65% saline environment reveals improved corrosion rate of NiZnP modified Al₂O₃. The surface site of the crystal formation evolves perfectly with hexagonal structure seen along the grain boundaries.