Papers by Keyword: Fracture Analysis

Abstract: This study investigates the stress intensity factors (SIFs) in cylindrical pressure vessels with nozzles, focusing on the effect of nozzle offset on crack behavior. Cracks are positioned on the inner wall of the cylinder at the nozzle intersection, and their location remains constant while the nozzle is systematically offset on the cylindrical surface. The analysis aims to determine how varying nozzle positions influence the SIFs, providing critical insights into structural integrity under different loading conditions. The study employs finite element analysis (FEA) to model the stress distribution and crack propagation behavior for various nozzle offset scenarios. Results highlight the sensitivity of SIFs to nozzle displacement and emphasize the importance of precise positioning in pressure vessel design to prevent crack propagation and failure. These findings offer practical implications for optimizing pressure vessel and nozzle designs in industrial applications, ensuring enhanced safety and reliability.

Abstract: This study investigates how heat treatment affects the mechanical properties and microstructure of extruded AA2017 aluminum alloy. Quenching (icy water vs. liquid nitrogen) and tempering (T6: 120–160°C; T7: 240°C) significantly alter hardness, tensile strength, and fatigue life. T6 promotes fine, coherent precipitates, enhancing strength and fatigue resistance, while T7 leads to over-aging and property degradation [X]. Icy water quenching improves fatigue life over liquid nitrogen by refining precipitates [Y]. Microstructural analysis reveals elastic adaptation (T6) and plastic shakedown (T7) as fatigue stabilization mechanisms, with fracture modes shifting from ductile (T6) to mixed ductile-brittle (T7) [Z]. These results optimize heat treatment for AA2017 in high-strength, fatigue-critical applications.

Abstract: Cast aluminium alloys are widely utilized in various industrial applications due to their favourable properties. A comparative analysis of fracture surfaces for EN AC 5083 cast aluminium alloy specimens processed in a single-pass by friction stir processing (FSP) and submerged friction stir processing (SFSP) has been carried out in this paper. Fracture surface evaluation involves mechanical tensile tests, microscopic investigations using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) to analyse the microstructure, fracture characteristics and elemental composition of the processed material. The findings provide valuable insights into the fracture behaviour of EN AC 5083 aluminium alloy FSP and SFSP processed, contributing to further research on optimizing friction stir processing techniques in ambient and submerged process conditions.

Abstract: The good environmental effect and possible cost reduction which can be achieved by reinforcing natural fibers in composites while improving some properties led to the development of these materials in various fields. In terms of mechanical properties of composites with natural fibers, both fiber loading and their orientation in the matrices are important factors. In this research work, the effects on the mechanical properties of reinforcing quasi-unidirectional salago fiber in epoxy resin were investigated. Varying alkaline treated fiber contents of 5 %, 10 % and 15 % by weight were characterized through tensile, flexural and impact tests. Fracture analysis after mechanical testing was done with the aid of optical microscopy. As the fiber weight content increases, results revealed enhancements on tensile strength, modulus of elasticity, flexural modulus and impact strength. Overall, the 15 wt. % fiber loading obtained the highest mechanical properties with average tensile and Izod impact strengths of 89.2 MPa and 137 J/m, respectively.

Abstract: The effect of segregation defect of SiC particles on the properties of materials was studied. 15% SiCp/2009Al composites were prepared by powder metallurgy (PM). Special SiC/Al samples were added to 15% SiCp/2009Al composites. These SiC/Al samples with different sizes and volume fractions were 25%, 35%, 45% and 60%, respectively, which resulted in SiC particulates segregation defect. The 15% SiCp/2009Al composites with defects were tested by ultrasonic testing. Tensile samples were obtained at the locations, where defects might be detected and the mechanical properties were tested. The results showed that all defective samples were cracked at the defective location. The difference in tensile strength between the samples of defect and the samples without defect was large. The toughness of the sample containing the defect reduced and the brittleness increased. The dimples on the matrix indicate that ductile fracture occurred during the fracture process. The cleavage fracture or cracking of the SiC particulates indicated that the stress can be effectively transferred from the matrix to the particles, and the particulates strengthen the matrix well. However, the sample with defect led to brittle fracture in the defect, and a crack source produced at the interface, resulting in a significant decrease in the mechanical properties of the material. If the inhomogeneous distribution of particulate containing a large area was found in the ultrasonic testing of the aluminum matrix composites, the tensile properties of the products generally cannot meet the requirement for application.

Abstract: The 2011 Tohoku Earthquake ruptured multiple faults simultaneously, generating strong ground motions over a long duration at long periods. Such severe events have recently begun to be considered in structural design, requiring explicit calculation of the low cycle fatigue capacity and fracture point. This paper presents a numerical study of dual moment and braced frames, with either conventional or buckling-restrained braces. Both brace and beam end fracture is considered, and incremental dynamic analysis (IDA) used to determine the ultimate failure mechanism under extremely large ground motions. Fragility curves are generated, demonstrating the significant role that member fracture has on the seismic performance of braced frames.

Abstract: Fracture of concentric braced frames due to local buckling under cyclic loading often requires computationally intensive 3D shell models. For practical design, the authors have previously proposed a phenomenological stick model that accurately captures local fracture, referred to as the Direct Local Strain Evaluation Method. However, the accuracy of the proposed method has previously only been validated using quasi-static cyclic component tests. This research extends this work, validating the method under dynamic loading conditions using numerical studies and in-frame shake table testing. The method is shown to be in good agreement with the global response and to accurately capture fracture due to local buckling under cyclic dynamic loads.

Abstract: Additive technologies are replacing the conventional methods of casting and subsequent time-consuming machining because of its high productivity. Resent engineering development in the field of additive manufacturing allows increasing assortment of useful powder materials. Technology of high-speed direct laser deposition (HSDLD) is a one of most perspective new technologies. It allows realizing heterophase process during the manufacturing, which there is process of partial melting of used powder is realized. The product is formed from a metal powder, which is supplied by compressed gas-powder jet directly into the laser action zone, wherein the jet can be as coaxial and as non-coaxial. Ni-based alloys found their application in many industrial areas, mostly there are used engine systems, aircraft and shipbuilding, aeronautics. The unique combination of operational characteristics depending on the type of alloy makes them promising materials. Heating and cooling rates during direct laser deposition determine structure and affect on its properties. Research is focused on structure and phase formation within technological process of HSDLD for Ni-base superalloys. Mechanical tests were carried out on the static tensile test, microhardness was measured. Based on research results the high-speed direct laser deposition technology could be used for manufacturing of products from different Ni-based alloys without subsequent heat treatment.

Abstract: Ni-based superalloys are used as turbine blade material in which creep-fatigue is an important damage mechanism. Simulation and experiment methods are used to investigate and predicte the failure mechanism of the first stage high pressure turbine blades of an aeroengine after 600 hours service. The high pressure turbine blades were made of Ni-base superalloy DZ4, fabricated by DS investment casting. The largest stress point was obtained by finite element analysis. During the fatigue test, the high temperature and low cycle fatigue/creep load simulating the real working condition were applied on the blades until they fractured. And then several examinations were carried out to identify the fracture’s main cause, such as visual examination, SEM fractography and microstructural characterization. In conclusion, the fracture of the high pressure turbine blades was mainly caused by the interaction of the fatigue and creep. Besides, the oxidation accelerated the blades fracture.

Abstract: Environmentally correct composites, made from natural fibers, are among the most investigated and applied today. In this paper, the mechanical behavior of epoxy matrix composites reinforced with continuous buriti fiber, through bending tensile tests was investigated. Specimens containing 0, 10, 20 and 30% in volume of buriti fiber were aligned along the entire length of a mold to create plates of these composites. The plates were cut following the ASTM standard to obtained bending test specimens. The test was conducted in an Instron Machine and the fractured specimens were analyzed by SEM. The results showed an increase in the materials flexural properties with the increase in volume fraction of buriti fiber.