查看更多>>摘要：? 2021The deviations between characteristic parameters of some individual samples and statistical expectations are relatively large because of the material dispersion. To solve this problem, a mean value updating and compensation algorithm for failure criteria based on heuristic maximum a posteriori estimation has been proposed, the failure criterion would be updated with new samples, the difference between new and old failure criteria would be used to compensate for the new sample to improve the accuracy of the fault diagnosis of the material damage to the gearbox shell. In this study, a failure mode of tensile damage has been done and the effectiveness of this method has been demonstrated.
查看更多>>摘要：? 2022 Elsevier LtdThe centrifuge test is considered as a promising alternative to the traditional, usually time-consuming mechanical tests of adhesive joints mainly due to its limited testing time and multi-sample testing capability. The present paper reports the first attempt to simulate the centrifugal loading of adhesive joints. To this end, a composite-to-metal adhesive joint was modeled and analyzed using the LS-Dyna explicit finite element software. Debonding was simulated using the cohesive zone modeling approach. The model was capable to predict the adhesion strength of the joint. Using the model, the effects of computing parameters (mesh density, loading rate) and geometrical parameters (adhesive thickness and diameter) on the adhesion strength were evaluated. The predicted adhesion strength values of the joints agreed very well with experimentally measured values obtained from a previous work of the authors. More specifically, simulating smaller adhesive diameters led to strength reduction, so did the alternation of the standard film thickness. The model can be potentially used to optimize the centrifuge test of adhesive joints and for virtual testing.
查看更多>>摘要：? 2022 Elsevier LtdAdditive technology has recently grown from experimental rapid prototyping to the production of functional engineering components for various applications, but the inherent quality of additive manufacturing and significantly weaker mechanical properties in comparison with traditional manufacturing still limit their application. Hence, a modified fused deposition modeling (FDM) method which allows the structure to be selectively reinforced with continuous fiber reinforcement results in composite structures with improved mechanical properties. It has indications of notable deviation from the classical laminate theory (CLT) theory and the rule of mixture, as well as a significant influence of manufacturing defects on the overall mechanical properties. Although the results in the mechanical behavior analysis of these materials are scarce today, authors up to date have documented some mechanical properties under tensile loading without interruption. Those experimental data lack the stress–strain relationship response in the unloading stages, thus missing the possibility of plastic strain determination. Therefore, eight sets of continuous carbon fiber reinforced thermoplastic composite (CFRTP) test specimens were designed and additively manufactured according to ASTM-D3039 for different fiber volume fractions and layer stacking sequences of 0/90, ?30/30, ?45/45, ?60/60. Moreover, specimens were prepared by milling the unnecessary edges, and the layup surface was treated to achieve a stochastically paint pattern for digital image correlation (DIC) tracking. Finally, the prepared specimens were statically tested over three consecutive phases of progressive tensile loading and unloading, while the displacements were monitored and measured using the GOM-Aramis DIC system.
查看更多>>摘要：? 2022Transient blade loading limits the lifetime of turbocharger turbine blades. This study investigates the flutter instability of a radial turbocharger turbine blade under pulsating inlet conditions. The viscous Navier-Stokes equations with the SST-kω turbulence model and curvature correction were solved. A time-marching 3D finite volume method was used in the CFX17 CFD solver to model the vibrating blade in a traveling wave mode applying Fourier Transformation. For flutter calculations, moving boundaries with specified modal displacements were used. An area of instability was recognized on the suction-side of the rotor blade. FSI steady-state analysis was then performed to assess the effects of shock position and blade profile on the blade stability in the recognized vulnerable region. The results show that a higher trailing edge radius increases the stability and leads to a significant reduction of flutter risk whereas the maximum thickness and leading-edge radius do not notably affect the flutter occurrences.
查看更多>>摘要：? 2022 Elsevier LtdOne of very common defects of bolt products are failures resulting from the plastic forming processes of materials. Surface discontinuity defects can take the form of folds, forging laps and cracks. These defects are known phenomenon associated with the production of bolt products, and they are described in the standard DIN EN 26157–3. The reasons for their formation may be different and the knowledge about improving the quality of bolt products is very important. Prevention of these defects is one of the key issues related to an improvement of product quality and implementation of a new bolt technology. The work presents and analyzes mechanisms of generating forging laps and cracks formed in a four- and five-stage cold forming processes of bolts. Three cases of defect generating were selected and analyzed using numerical simulations by the QForm3D software. The FEM results were compared with results of an experiment of bolt forging on a forging machine. In the first case, the influence of the volume of the material determined on the forging of the bolt head was examined. A variant with a constant volume and a variant with a volume that changed with successive stages were prepared. In the second case, dies with different geometry were used (constant or graded corner radii dies shaping the transition of the pin into the bearing surface of the bolt). In the third case, the shaping of the bearing surface of the bolt in one or two steps of forging was considered. Potential errors in the design of the process of shaping the bearing surface and threats in further use of bolts were indicated. Forging laps and cracks based on the microstructure of the material flow lines, photos and FEM simulations were presented.
查看更多>>摘要：? 2022 Elsevier LtdIn a process gas synthesis for ammonia production, steam precursors are produced in a shell and tube heat exchanger (HE), called a waste heat boiler (WHB), because it uses heat from a gaseous produced in the reformer. The process gas flows in the tube, and a saturated water-steam mixture is on the outer shell side. In many cases, the waste heat boiler fails because of corrosion, erosion, and a combination of both. In this present work, a new failure mechanism of WHB tube is reported. The tube failed due to excessive oxidation wastage and had black products on the water-steam side. The oxide product was magnetite, intact on the surface, and the water-steam flow eroded some. The microstructure of the failed tube was composed of pearlite and ferrite without observed degradation. A computational model based on computational fluid dynamics revealed flow recirculation attributed to sudden enlargement at the end of the ferrule. This created high heat flux at some distance from the ferrule end; consequently, the tube excessively oxidized because of the high heat flux and temperature gradient across the tube thickness. This study provides a basis for developing HE designs and exploring the damage mechanism of shell and tube heat exchangers.
查看更多>>摘要：? 2022 Elsevier LtdThe polygonal wear is a significant concern in railway engineering, and the mechanism behind it remains elusive. In this study, the polygonal wear on a specific metro line in China is analyzed. The 7th-order and 8th-order wheel polygonal wear are commonly measured on the metro, in which corresponding excitation frequency is located in the 44.3–58.9 Hz interval at the operating speeds of 60–70 km/h. Meanwhile, an obvious natural resonance at 50.7 Hz is found by analyzing the acceleration of axle box, which is verified by the eigen analysis of the corresponding metro track. Moreover, the vehicle-track coupling model with polygonal wheel is established to analyze the vertical wheel/rail forces induced by polygonal wear. The result indicates that the P2 resonance is the main contributor to the high amplitude vertical wheel/rail forces, which is also the main factor for development of polygonal wear after formation.
查看更多>>摘要：? 2022Excessive tool wear seriously affects the surface quality of the workpiece and reduces the processing efficiency. Therefore, real-time monitoring of the tool wear status is very important. This paper proposes a new tool wear prediction method based on multi-sensor hybrid domain information fusion. First, the collected multi-sensor signals are decomposed by wavelet packet to extract the energy values of 16 frequency bands; in addition, the energy values are combined with the time domain and frequency domain features to construct a hybrid domain feature set; then, the gated recurrent unit model is used to adaptively explore the internal relationship between the hybrid domain features and tool wear, which overcomes the low efficiency of manual feature fusion monitoring; finally, the wear milling cutter data is used to verify the superiority of the proposed method. The results show that the prediction accuracy of tool wear based on multi-sensor feature fusion is significantly better than that based on a single sensor. Also, compared with traditional wear prediction methods, it again verifies the advancement of the proposed method in predicting tool wear.
查看更多>>摘要：? 2022 Elsevier LtdThe issue of containment stems from the aero-engine field, and there is little research in the turbocharger field. In order to reduce the number of tests, development cycle and cost, it is necessary to predict the burst speed of the turbine accurately. In response to this problem, a coupled plasticity-damage model is developed for turbine materials according to the stress state and operating temperature of the turbine. The effect of stress triaxiality, temperature are considered in the plastic constitutive and the failure criterion. The stress update algorithm of plasticity-damage model is given. According to the operating temperature and stress state of the turbine, the experimental scheme of K418 nikel-base superalloy is designed to calibrate the plasticity-damage model. Finally, the coupled plasticity-damage model is verified by the specimens with the notch radius R6 at 550 °C and 600 °C. The results show that the maximum error of proposed model is about 7.3%, which is better than the 14.2% prediction error of the constitutive model without any corrections. Moreover, the failure displacement can be predicted by the proposed constitutive model (the maximum error is about 8.2%), which is beyond the ability of traditional model. The location of failure initiation, fracture pattern in numerical studies have also showed close correspondence to the experimental results.
查看更多>>摘要：? 2022 Elsevier LtdPlates are widely used for lightweight structures in various disciplines, e.g. aircraft construction. However, these plates are susceptible to lateral forces due to impacts from falling tools, bird strikes, collisions with objects, etc. These impacts can occur anywhere on the plate. Here we report the dependence of the impact location on the impact itself. We use a semi-analytical approach that is verified in a code-to-code analysis using a commercial FE solver. Based on this code, a strong dependence of the impact location as well as the mass ratio of impactor and plate is found for the plate deflection and contact force. In addition, a general explanation for impact events is developed, leading to the distinction between small and large mass impacts. This work supports previous findings on the influence of mass ratio and completes the understanding of impact events at arbitrary locations.
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