The high-speed trains designed and constructed in Indonesia will use Aluminum alloy Al 6061-T6 as a structural material. Aluminum alloys are prone to fatigue failure due to the absence of endurance limit of the material, hence fatigue life prediction has to be carried out. Fatigue cracks could initiate at the defects of welded joints. Analyzing the fatigue load spectrum of critical locations in the train structures is crucial to predicting fatigue life. These critical locations are selected from areas with high static stress and stress concentration. The loads are analyzed using the multibody dynamic with rigid body assumptions and track roughness following UIC Standard Code 518. The finite element method is used to calculate the stresses from the loads generated by the multibody dynamic. The load sequence is further analyzed with rainflow counting method, and the load exceedance curve can be constructed. Finally, the Miner Linear Cumulative Damage Model is used to predict fatigue life.

BACKGROUND: The feed pipeline made from 30408 stainless steel of a new unit leaked during the air pressure test. OBJECTIVE: The present work aims to examine the specific cause of pipeline cracking, and providing effective approaches to avoid similar failures. METHODS: Macroscopic inspections of the cracked pipe defects were made on site immediately after leakage. Mechanical properties and hardness of specimens machined from the failed pipe were tested. In addition, microscopic analyses including material composition, microstructure observation and crack morphologies of the failed part were performed to get detail information. Composition of the feed raw material was also analyzed to identify whether it had been contaminated by corrosive elements or not. RESULTS: No impurity composition was found in the feed raw material. The element constituents, yield strength, tensile strength and hardness of the cracked pipe fulfill standard requirements. A number of scratches and defects with a size of several microns were found on the inner wall of the leaked pipe, and they were believed to be formed at the perforation step during pipeline processing. Liquation cracks were found at the pipeline butt weld joint, and they laid hidden dangers for the safety and steady operation of the pipeline. CONCLUSION: The overall analysis results indicated the pipeline leakage during air pressure test was caused by cracks initiated around inner wall defects, which sabotaged the bearing capacity of the pipe by wall thickness reduction and stress concentration. Therefore, improving the inner wall surface quality at the perforation step may help to avoid such failure. The metallurgical effect and weld stress caused during the welding process promoted the initiation and propagation of liquation cracks. The tendency of welding hot crack formation could be reduced by taking strict composition control of the welding rod and adopting reasonable welding parameters.

Blowout preventer reliability is important for safe drilling operation. In order to study the sealing mechanism and failure mechanism of conical blowout preventer, a numerical model of conical blowout preventer was established based on the theory of large deformation of rubber, and the deformation law, stress distribution and sealing performance of rubber core in well shut-in operation were studied. The results show that there are stress concentrations in the contact area between the rubber core and the piston, the grooves in the middle of the adjacent support ribs, and the chamfered corner of the inner wall of the rubber core, the main form of failure at these locations is rubber cracking. Higher stress is present in the neck region of the upper plate and the back region of the lower plate of the support ribs. The inner wall surface of the rubber core gradually produces stripes of wrinkles, and the smaller the size of the sealed drill pipe, the more obvious the wrinkles are. When the drill pipe joint is sealed by the rubber core, there is a sealing buffer zone at the shoulder, and the contact pressure change abruptly. The lower portion of the rubber core’s inner wall serves as the primary sealing area. Increasing the piston displacement appropriately can enhance the sealing performance of the rubber core. The results can provide a theoretical basis for the optimization design of the conical blowout preventer.

Piezoelectric materials are widely used in electronic devices like sensors. In this study, a strip saturation zone model is provided for a transversely isotropic piezoelectric plate which is cut along three equal collinear impermeable cracks. The developed saturation zones are assumed to be subjected to the linearly varying electric displacement conditions. The problem is solved using Stroh formalism and the complex variable approach. Analytic closed-form expressions are obtained for fracture parameters including crack opening displacement, crack opening potential, and saturation zone length. A numerical study also presented showing the effect of linearly varying electric displacement on the saturation zone length.

In this work, two reinforcements (natural jute fiber and glass fiber) hybridized with different volume fractions, are reinforced with a constant volume epoxy resin through hand layup method. The ASTM standard tensile specimen of jute natural epoxy composite of different volume fractions and orientations of fibers, with varied single edge notch (SEN) size were subjected to uniaxial tensile load in universal testing machine. Effect of jute volume fraction, notch size and fiber orientation on tensile strength and fracture toughness has been studied through experimental results. Increased percent of jute fibre showed decrease in tensile strength and fracture toughness. Also, with the increase in notch size, the tensile strength decreased and the fracture toughness increased. Further, the tensile strength and fracture toughness were superior in 0°/90° fiber orientation specimen than those with ±45° fiber orientation. Furthermore, experimental results were validated by conducting statistical and fractographic analysis. The jute fiber percentage was ranked as best level factor affecting the fracture behavior as per taguchi method. Morphological features of fractured surfaces were analyzed through scanning electron microscopic (SEM) images with respect to nature of jute fiber failure under uniaxial loading conditions.

This study examined the failure mechanism of fiber-wound composite pipe and determined the optimum winding angle. Simulation models of glass fiber-wound composite pipe were established. Failure factor of the reinforced layer of fiber-wound composite pipes under internal pressure, torsion, axial tension and bending load are investigated in conjunction with the three-dimensional Tsai-Wu failure criterion. The results show that the winding angle has a significant effect on the stress distribution of the reinforced layer. The inner layer of the reinforced layer is prone to failure under internal pressure. The outer layer of reinforcement layer under torsion is the easy failure position. The failure-prone layer under tensile load is related to the winding angle. The inner layer of the reinforced layer is prone to failure when the winding angle is less than 60°, and the outer layer is prone to failure when the winding angle is more than 60°. The outer reinforced layer is prone to failure under bending loads. When the winding angle is less than 50°, the easily failed failure position is on the inside of bending. When the winding angle is greater than 50°, the easily failed position is on the outside of bending. The smaller winding angle is conducive to improve the tensile, bending and torsion resistance of the composite pipe. The larger winding angle is beneficial for improving resistance to internal pressure. The optimal winding angle range for each load is different and multiple winding angles should be used in the design to obtain a higher overall load carrying capacity. The research results can provide a theoretical basis for the improved design, manufacture and evaluation of fiber-wound composite pipes.

In order to investigate new crack generation in thermally tempered glass, crack propagation and crack divergence were observed using Cranz-Schardin high speed camera. Tempered glass of 3.5 mm thick was used as a specimen. Generation of cracks due to two crack-collision was also observed in 3.5 mm tempered glass, as well as those observed by Caustics method in 10 mm thick tempered glass. Regarding the presence/absence of new cracks the dependence of two cracks on the collision angle was confirmed. Considering that it is based on the synthesis of stress 𝜎CR generated at the crack tip, tensile stress necessary for the new crack generation could be created.

Brittle materials such as ceramics are subject to fracture without warning. Because non-destructive techniques are unreliable for determining potential fracture sources in ceramic materials one must rely on statistical analysis of laboratory strength data. This data is used to determine the minimum strength, and its uncertainty, of a set of specimens, and then must translate this laboratory data into a projection of the reliability of components manufactured from the material. This paper sets forth new guidelines for the choice of a statistical methodology to fit the laboratory data and puts forth a procedure – known as tolerance limits and coverage – to extrapolate this data to predict component reliability. Data on a borosilicate glass is used to demonstrate the usefulness of this procedure.

BACKGROUND: Structural integrity assessment of components containing cracks is of paramount importance when they are part of critical structures. In this context, the fracture behavior of components containing cracks is crucial. OBJECTIVE: To investigate the effect of the diameter, number and position of holes drilled in the vicinity of the centre crack in a finite plate on the mode I stress intensity factor (SIF). METHODS: A 2D model with central horizontal crack was created in ABAQUS® simulation software and validated with the analytical results after performing mesh convergence. Circular holes of different diameters and at different positions were then introduced in the vicinity of the crack. RESULTS: By increasing the diameter of the hole and its number, the SIF reduced significantly. An optimum amount of distance between the crack and the hole was found at which the SIF was minimum, beyond it increased and asymptotically approached that of the plate without holes. CONCLUSION: The diameter of the hole and the spcacing between the hole-centre and the crack axis has a major influence on the mode I SIF. By introducing multiple holes, the mode I SIF significantly reduced.

Although ductile fracture properties of aluminum alloy have been examined by several research works, the effect of strain rate in small punch test is still unclear. An investigation on rate sensitivity of fracture mechanical characteristics of aluminum alloy in small punch test is necessary. In the present study, an experimental investigation of small punch test is performed at different deformation rate in quasi-static test for aluminum alloy 1050-H14. The strain-rate sensitivity of fracture properties are discussed based on the force-deflection curve as well as observation of fracture surface of deformed specimen after testing. The obtained results show that the material possesses a positive rate-sensitivity in the investigated range of displacement rate from 0.48 to 1.26 mm/min. The necking appears in a small region due to inhomogeneous deformation in the direction of cross-section at lower deformation rate. In the case of higher rate of deformation, more uniform deformation in the direction of cross-section and the local ductile fracture with more dimples can be observed.