Papers by Keyword: Fracture

Abstract: We have developed a new testing device which is capable of detecting hydrogen gas release during slow strain rate tensile testing (SSRT) under ordinary pressure. The device is composed of an SSRT machine equipped with a closed chamber with an inspection window that is connected to gas chromatography with a semiconductor hydrogen sensor. Local strain distribution in the specimen during the SSRT is monitored dynamically with a digital image correlation (DIC) method. Hydrogen was pre-charged to aluminum alloys by means of friction in water process. Using the device, it was shown that hydrogen was released particularly in the stage of plastic deformation and fracture. In addition, the hydrogen gas release at the moment of fracture was clearly increased when the alloys were hydrogen-charged and tested at a slow strain rate. When we calculated hydrogen gas release from the fracture surface in Al-Zn-Mg base alloys tested at 3.3×10^-6 s^-1, the hydrogen amount was estimated to be 6.24×10^-10 mol /mm² in a hydrogen-uncharged alloy, and 1.30×10^-9 mol / mm² in a hydrogen-charged alloy.

Abstract: The paper focuses on the metallographic analysis of the damaged inner shaft of a centrifugal pump with a magnetic clutch. This pump was used for the pumping of viscous suspensions. The damaged part of the centrifugal pump was made of stainless steel and transmitted power from the magnetic clutch to the impeller of the pump. The pump was overhauled by the Manufacturer after ten years of routine work. Slightly worn parts of the pump, including the inner stainless steel shaft, were replaced by the Manufacturer according to the preserved documentation. The overhauled pump failed after two days of running in the original conditions. The problematic is solved by an analysis of three used inner shafts with the aid of a metallographic analysis of the microstructure of the material, using light microscopy and scanning electron microscopy, and an EDS microanalysis of the chemical composition and hardness measurements.

Abstract: This paper focus on evaluation of behavior, damage and failure processes occurring during the loading cycles in the carbon fiber reinforced composite by acoustic emission method. Since acoustic emission is physical phenomenon that detects the released energy in form of waves spreading through the material due to stimulation of material by external or internal stress, it is possible to evaluate complex damage and failure processes. For that purpose, the standard and open holes tensile testing specimens with different number of plies were manufactured. Selected acoustic emission parameters were correlated with data obtained from mechanical test. Linear localization method together with signal analysis using Fast Fourier transform algorithm were used as another tool for detection and evaluation of spreading damage processes inside the composite during the load. Basic damage types inside the composite material were identified by metallographic analysis using light microscopy. More complex damage processes were observed on the fracture surface using stereomicroscopy and scanning electron microscopy.

Abstract: Fractures resulting from wear and fatigue process have been identified as the main causes of failure in biomaterials, especially in implants that act in place of bone or other hard tissue, as they are subject to conditions involving severe cyclic loadings. In biomaterialscase, the types of failures mentioned above must also be evaluated under the effect of degradation or corrosion, due to the direct contact with body fluids. The present research analyzed the fatigue induced by corrosion fracture of an orthopaedic implant for total knee replacementproduced with an austenitic ASTM F138 stainless steel. The morphology, compositions of the interfaces and subsequent corrosive pitting were characterized by stereoscopy and scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS). Stress concentration, inclusions and high carbon levels were the main reasons of failure.

Abstract: The structural features of epoxy polymer samples of different thicknesses under the influence of thermal energy are studied. The structure of fracture patterns of epoxy polymers, which are intensively structured in the thermal field, is investigated. The optimum temperature and duration of exposure are determined, which allows intensive production of products based on epoxy polymers with high physical and mechanical characteristics.

Abstract: In metastable beta Ti alloys, microstructural features can be varied over a wide range of length scales by changing different heat treatment parameters. Effect of cooling methods on microstructure and mechanical properties of Ti-3537 alloy after solution treatment was investigated. The result shows that with the decrease of cooling rate, the Vickers hardness of the alloy gradually increases. Among the three cooling methods of OQ, AC and FC, Ti-3573 alloy has the best shape and moderate yield strength, but tensile strength. The fractography of the β-substrate specimens showed that the fracture mode was ductile fracture. In the FC state, the α phase precipitates in a large amount in the Ti-3573 alloy, the yield strength and the tensile strength are greatly increased and the elongation is remarkably lowered. The tensile fracture shows a shallow fracture dip with low toughness.

Abstract: Mechanical failure of zeolite-high density polyethylene (HDPE) material applied to skull bone implants is a material fracture that cannot be controlled. An important step to minimize failure due to fracture is to understand the fracture characteristics indicated by the propagation path pattern. This study aimed to investigate the fracture propagation pathways of zeolite-HDPE composites in quasi-static conditions. UV-irradiated Double-edge cracked zeolite-HDPE composite was tested in mode I (a stress perpendicular to the plane of the crack) in a universal testing machine (UTM) with a crosshead speed of 2 mm/min at a constant room temperature of approximately 25°C. The stress and elongation were registered by the UTM. During loading, the evolution of cracks in the ligament length region was recorded with the camera so that the crack propagation pathway until the total fracture occurs can be clearly observed. The results show that the crack propagation pathway patterns were not all straight and parallel to the ligament length. They are also found in a deviant state of the ligament length line by forming an angle α. created between the ligament length line and the fracture propagation deviation direction. This deviation occurs after the crack propagates straight away from the initial-cracks.

Abstract: This study focuses on problems of treatment of proximal humeral fractures occurring against the background of osteoporosis. It presents statistics on osteoporosis and lower energy trauma among patients in the Russian Federation and abroad. The high susceptibility to osteoporotic changes in the bone structure of the male population of Russia compared to the global statistics of osteoporosis among men was emphasized. The main classifications used in the clinical practice of orthopedists and traumatologists allow to identify the type of fracture by clinical and anatomical basis and to structure the existing patient management tactics to achieve the most optimal result of treatment and restoration of limb function. There is an analysis of publications representing various methods of fracture treatment, which helps to use the most optimal methods of relevant fractures treatment.

Abstract: There was an oil pipeline fracture found in the unlock process of Z well in western oilfield.The reason that made the oil tube fracturewassystematically studied usingmacroscopic analysis,physical and chemical property test,scanning electron microscope with an energy dispersive X-ray spectrometer and X-ray diffraction analysis.The results suggested that the requirement of relevant standard for C110 steel grade was satisfied with the chemical component and mechanical property of oil tube.The perforation of oil tube made H₂S in the fluid medium enter the oil set of connected rings. In addition, the high-pressure gas left by gas contained certain H₂S and O₂ so that the tubewould fracture and be invalid under the combined action of sulfide stress corrosion and oxygen corrosion.

Abstract: Benefit from the gradient distribution of microstructure, gradient nanograined (GNG) metals have broad application prospect owing to their advantages of both high strength and good tensile ductility. Meanwhile, the fracture behavior of gradient nanograined metals is different from that of traditional homogeneous materials. Using molecular dynamics (MD) method, we simulated the propagation of a crack in a pre-cracked GNG Cu. Voronoi method was adopted to generate the polycrystalline topology with gradient grain size, and FCC copper atoms were filled into the topological structure. The crack was introduced by removing three layers of atoms. Then, the MD specimen was loaded to simulate the crack growth and/or blunting. The micro-defects were identified by the common neighbor analysis parameter. The effects of the grain size gradient and the crack tip initial position on the crack growth were also investigated.