查看更多>>摘要：A low-pressure steam turbine blade failed at a thermal power plant reported in this paper. Few blades were damaged on the exhaust side, and the cracks originated on the trailing edge and spread toward the leading edge of blade. In the crack initiation point, shallow corrosion pits were evident, however, turbine vibrations were found to be actuating crack initiation and propagation. Due to numerous pits observed on blades surface, there were vibrations. A pressure drop on the exhaust side of the steam turbine caused condensation and water droplets impinging on the blades caused severe erosion. Upon contact with the condensed water droplets, the chromium carbide precipitates in the martensitic matrix converted into chrome oxides, and impingement of high velocity steam erodes these oxides, causing a rough surface with honeycombed texture. As a result of the roughened blade surfaces, fatigue cracks form at potentially weaker areas and subsequently the final fracture.
查看更多>>摘要：Achieving a reliable prediction of damage evolution behavior in ductile metals is among the most important challenges of researchers. In this paper, first, based on continuum damage mechanics (CDM) and Lemaitre's ductile damage model, a VUMAT subroutine is developed and implemented into the Abaqus/Explicit code. A lately proposed numerical method is applied to determine material dependent damage parameter for ductile metals like AL-5052 H32 aluminum and X30Cr13 steel alloys. Then, the model is employed to assess damage evolution behavior in different ductile sheet metals and shapes. Finally, the numerical simulation results of damage initiation, growth, and crack onset are attained and validated by experimental and contributed results of literature. It is concluded that the recently presented numerical method in combination with the CDM-based Lemaitre's ductile damage model can successfully estimate the Lemaitre's ductile damage parameter and accurately predict damage evolution behavior of ductile metals under different loading and boundary conditions.
查看更多>>摘要：Examining the creep behavior of materials locally provides important information about material performance. In this study, IN625 powder was layered on GTD-111 superalloy by the laser cladding (LC) method. After LC, the creep behavior of the clad zone (CZ), substrate, and heat affected zone (HAZ) was investigated by the small punch creep test (SPCT) method. The results showed that the CZ has the highest creep life. This was attributed to the widespread presence of equiaxed grains, high volume fraction and fineness of the gamma ' phase as well as NbC carbide particles. The HAZ region, on the other hand, had the shortest creep life due to the dissolution of gamma ' particles during LC. gamma ' phase in the substrate and gamma '' phase in CZ, the most important obstacles to dislocations movement during creep were identified, among which gamma '' particles were superior to gamma ' particles in the substrate due to their high volume fraction and fineness. The results of microhardness also confirmed this.
Santharaguru, N.Abdullah, S.Chin, C. H.Singh, S. S. K....
26页
查看更多>>摘要：This study aims to determine the appropriate frequency domain methods for durability predictions of lower suspension arm based on real-life random vibration data. In frequency domain, the power spectral densities (PSD) of the vibration signals were obtained and then analysed using three PSD cycle counting models, including the Lalanne, Dirlik and Narrowband methods. Correlation between fatigue lives predicted by time domain and frequency domain methods were evaluated to determine the appropriate frequency domain methods for durability prediction suspension lower control arm. Results show good correlation between fatigue life predicted with vibration fatigue and strain-life approaches. Therefore, it was deduced that road surfaces affect the fatigue life of the lower control arm, whereby the rougher the surface, the lower the fatigue life of the lower control arm. Lalanne and Dirlik PSD cycle counting algorithm were found to be the most suitable method for vibration fatigue analysis of lower suspension arm.
查看更多>>摘要：In real-world applications, machinery operates under non-stationary conditions such as operating environment, failure modes, and noise where domain shift problems generally arise. Hence, deep learning methods are trained on one working condition cannot generalize effectively on different conditions. Also, the suitability of prognostic features significantly affects the prediction results. To address these issues, this paper proposes a transfer learning-based bi-directional Long ShortTerm Memory (TBiLSTM) network for extracting prognostic sensitive features, and domain adaptation is realized using multi-kernel maximum mean discrepancy (MK-MMD). Therefore, the proposed TBiLSTM network can be utilized for RUL prediction of bearings under multiple working conditions. The superiority and effectiveness of the TBiLSTM method are validated by both experimentation and comparison with state-of-art methods. In addition to this, prediction results demonstrate its effectiveness on IEEE PHM challenge datasets. Hence, the results demonstrate that the prognostic features are more reliable and domain-invariant for RUL prediction.
查看更多>>摘要：Flow-drilling screw (FDS) is a new type of single-sided joining process that is increasingly used to join dissimilar aluminum alloys in automobile lightweight. Fatigue failure and high-speed collision may occur in automotive joints under actual service conditions. This study proposed a joining process combining FDS and adhesive bonding to join dissimilar aluminum alloy sheets commonly used in body manufacturing. The adhesive bonding improved the joint strength and increased the failure distance of FDS joint. A thorough study of the FDS-bonding joining process on the mechanical properties and failure behavior was conducted. Specifically, a finite element analysis (FEA) model was built to predict the plastic deformation and stress distribution of the joints. Microstructure and hardness tests of the joints were performed to study the effect of plastic deformation during the joining process. The comparison of the mechanical properties and failure behavior of joints in dynamic tensile and quasi-static tensile tests showed differences and strain rate sensitivity. In addition, the maximum load-fatigue life (F-N) curves of dissimilar aluminum alloy joining were obtained by fatigue tests to predict the fatigue strength and failure life of the joints. Furthermore, the relationship between failure mechanisms and mechanical properties was established. This work provides a new industrial solution and failure performance reference for the requirement of composite structure and often one-sided access connection position in automobile industry.
查看更多>>摘要：The Low Cycle Fatigue (LCF) performance of an aero-engine bracket in a 'struts and connectors' design, made using the Laser Powder Bed Fusion (LPBF) process has been studied using strain controlled LCF tests at different Strain Ranges (SR). From the cyclic test results, the bracket has demonstrated that it meets the target LCF performance which was in excess of the normal expected operating loads that the LPBF bracket would experience. The failures in the bracket at different locations were observed only under the extreme loading conditions. The failure of the bracket was of a progressive nature with failure of different struts/connectors happening at different discrete cycles. Even after the first five failures, the LPBF bracket had 47% of the original load carrying capacity in the tensile part of the hysteresis loop, indicating a good redundancy in its load transfer paths. In general, the surface locations of the bracket struts/connectors, where there are lack of fusion voids, were the prime sites for crack initiation. If any of these locations also coincide with high stresses, i.e. the combination of 'size of defect' and 'magnitude of stress', then this will contribute to an increased likelihood of failure at these locations in the LPBF bracket.
查看更多>>摘要：A black powder material was discovered in the Liaohe oilfield that combusted when exposed to air. The black powder's phase and elemental compositions were investigated. The elemental valence was then determined using X-ray photoelectron spectroscopy (XPS) techniques. Immersion and electrochemical experiments were conducted in the laboratory using a high-pressure reactor to simulate the actual environment. The results revealed that the black powder's main components were iron oxide (Fe3O4), ferric polysulfides (Fe9S8), and sulfur and that the corrosion products of the immersion experiments were similar to the black powder examined on site. Fe9S8 and sulfur are responsible for the spontaneous combustion of the black powder. The corrosion rate of the X52 pipeline steel rose with increasing H2S levels, peaking at 14.15 mg/ m3. H2S, which came from underground gas storage, accounted for Fe9S8 and sulfur. Finally, filters and H2S removal devices should be installed to prevent black powder from spontaneously combusting.
查看更多>>摘要：Broken spikes/screws were reported to fail in bending at the sleeper hole due to repeated lateral force and have become a major challenge for hardwood timber sleepers. The emergence of polymeric based composite railway sleepers further highlighted this problem as they are perceived to have limited screw lateral restraint. It is thus significant to evaluate the lateral restraint behaviour of timber and the timber replacement composite sleepers. This study investigated the lateral strength of timber, synthetic composite and Ultra High Molecular Weight Polyethylene plastic sleepers at the standard required displacement of 5.1 mm as suggested by the American Railway Engineering and Maintenance-of-way Association and up to failure. The results showed screw yielding and sleeper material hardening even before 5.1 mm displacement while timber and synthetic composites exhibited ultimate lateral strength almost half of plastics' performance due to the relatively weak shear capacity in the fibre direction. The grain/fibre shearout failure was noticed in the orthotropic sleeper materials (timber and synthetic composites) while the isotropic material (plastic) mainly exhibited bearing failure. Based on the isotropic hardening rule and Hill's criterion, the developed finite element models predicted very well the screw lateral deformation and strength of timber and composite sleepers.
Zderic, IvanDimitrova, RositzaPetkov, VeselinSprecher, Christoph M....
20页
查看更多>>摘要：Two different orthopaedic implant designs of straight reconstruction and pancarpal arthrodesis plates with oval radiocarpal hole - both associated with clinically negative results - were initially subjected to laboratory cyclic fatigue testing in two independent biomechanical studies and presented with a fracture. Fractographic analysis was performed of each one randomly selected sample - Reco-Frac and OH-Frac. Reco-Frac fracture surface was characterized by three different plateau-like zones, distinguishing from each other by different topographies and fracture features. Complexity of the fracture was associated with a complex loading protocol. OH-Frac fracture surface revealed distinct radial marks originating at the bone-oriented side and was characterized with smeared metal and cleavage-like patterns. The fracture surface was more uniform, which can be ascribed to a simpler loading protocol. Clinically, fractures of the investigated two plate designs can be attributed to bone fracture healing disturbances, leading to prolonged cyclic loading of the plates and ultimately to their fatigue failure.
NSTL
Elsevier