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Mg-6Gd-3Y-0.5Zr (VW63K) alloy is widely used in the aerospace field because of its excellent mechanical properties not only at room temperature but also under high service temperature. In this study, the effect of minor changes to the Y alloying levels on the hot tearing behavior of VW63K alloys was researched by using a "T" mold, with pouring temperature of 720 °C and mold temperature of 150 °C. The results show that the hot tearing susceptibility of the alloy decreases gradually with the increase of Y content from 2.8 to 3.4 wt%. The reason for this phenomenon is that high content of Y element narrows the susceptible freezing range and increases the eutectic liquid fraction of the alloy, which is helpful for the alloy to have a better compensation at the late stage of solidification and, thereby decreasing the hot tearing susceptibility.

Carbon fiber-reinforced plastic (CFRP) composites are increasingly utilized in the aircraft manufacturing field due to their excellent properties of high specific strength/modulus, good corrosion resistance, flexible designability, and long fatigue life. But CFRP composites belong to typical difficult-to-cut materials, and tearing, burrs, and delamination can easily occur in its drilling process. Longitudinal-torsional coupled ultrasonic-assisted drilling (LTC-UAD) is a promising technology to suppress the drilling defects of CFRP composites, and thrust force and torque are significant factors affecting the drilling quality of CFRP composites. In this paper, a mechanical model for predicting thrust force and torque in LTC-UAD of CFRP composites is presented in terms of the spindle speed, feed rate, ultrasonic parameters, tool geometry, and workpiece material properties. The oblique cutting modeling is used for the cutting lip, and the corresponding cutting region is divided into chipping region, pressing region, and bouncing region, respectively. The chisel edge is regarded as a rigid wedge-shaped body extruding into the workpiece material, and the contact theory is utilized to obtain the contact force between the chisel edge and the workpiece material. Furthermore, longitudinal and torsional vibrations are introduced into the modeling of cutting force by considering the dynamic feed angle and dynamic uncut chip thickness. The accuracy of the model is verified by the drilling experiments, and the results show that the predicted values of the thrust force and torque are in good consistency with the measured ones. The maximum deviations of the predicted thrust force and torque compared to the measured values are 13% and 11%, respectively.

During wire and arc additive manufacturing (WAAM) of high nitrogen austenitic stainless steel (HNASS), the explosion of droplets with high-content nitrogen will induce grievous spatters, causing incomplete fusion, cracks and inclusions. In this study, the formation, characteristics and influence of spatters on cold metal transfer + pulse (CMT+P)-based WAAM of HNASS were investigated. The droplets exploded violently due to the sharp decrease of nitrogen solubility in liquid steel, which produced abundant spatters at the pulse stage. The spatter particles were a mixture of manganese oxides (MnO and Mn3O4) and molten metals of the wire. The overall particle size followed normal distribution. The majority of particles were spherically shaped in diameter of 20–150 µm, and over 80% of spatters were below 200 µm in diameter. Inclusion of manganese oxide spatter particles appeared in the deposition metals of single-pass single layer. The spatters at the root of the deposited metal can be hardly removed, which produced interpass defects in overlapping deposition. For multi-pass multilayer deposition, interlayer tearing occurred to reduce the mechanical properties of HNASS. The interlayer tearing was caused jointly by the incomplete fusion caused by spatter particles of manganese oxide and the large thermal stress. Hence, the spatters generated in the droplet transition for WAAM of HNASS must be controlled.

The deep drawing process is implemented for sheet metal forming in industries for acquiring the intricate shape of products and helping to maintain a high productivity rate. Failures viz. wrinkling, earing, tearing and fracture of the sheet metal, during this process are common. The aspects related to these failures are explored in this paper to reduce the occurrence of these failures. The latest method for analyzing failures is through simulation techniques in which numerical methods are combined with software packages. Different cases of failures and their corresponding method of analysis are discussed such as—effect of blank holder force, die shape, stress–strain development, contact pressure distribution, effect of die and blank holder shapes, wrinkling and fracture failures in sheet metal. Failures can be predicted from simulation for different product designs. The tool widely used for this is ANSYS which is found effective to obtain the desired results.

The research of casting properties especially the fluidity and hot tearing susceptibility is crucial for cast aluminum alloys. The fluidity and hot tearing susceptibility of two aluminum alloys were studied by three different methods (steel mold cast, thermal analysis and thermodynamic calculation), and the results were discussed in detail. The flow length and hot tearing susceptibility (HTS) of AlSi3.5Mg0.5Cu0.4 and A356 alloys were compared by using the spiral mold and constrained-rod cast mold, respectively. The solidification range (ΔTS) and dendrite coherency point (TDCP) were measured by cooling curve thermal analysis to explain the difference in fluidity of the two alloys, which reveals that the alloy with a smaller ΔTS and a lower TDCP will show a better fluidity. The thermal analysis results show that the alloys with a shorter “hot tearing sensitive range” can obtain lower hot tearing susceptibility. A hot tearing mechanism of the two aluminum alloys was proposed, that is, the hot tear initiates at the end of solidification and propagates along the liquid film. The thermodynamic calculation with Thermo-Calc software was proved to be an accurate and simple method to compare and analyze the fluidity and hot tearing susceptibility of aluminum alloys.

High-quality micro-holes play an important role in modern industry. However, in micro-hole drilling, a series of problems, such as chip removal and heat dissipation, restrict the improvement of micro-hole processing quality. Ultrasonic-assisted drilling (UAD) is a hybrid machining technology that combines conventional drilling (CD) with ultrasonic-assisted machining and it has great advantages when processing regular-size holes. This study mainly focuses on the influence of vibration amplitude in UAD on micro-holes manufacturing. By analyzing the cutting mode caused by periodic vibration in UAD, the influence of amplitude on the contact characteristics of the cutting edge and workpiece was studied regarding chip formation and separation ratio. Finite element simulations and experiments of micro-hole manufacturing using UAD and CD are conducted. The results show that the chip damage in UAD is more severe than CD, and as the amplitude increases, the chips became more fragmented. Compared with CD, in UAD, the thrust force is reduced by 20.1–30.05%. In addition, in UAD, the tool wear is better suppressed than in CD, and the increase in the amplitude ensures the integrity of the cutting edge. In CD, the morphology of the inner wall of the micro-hole is observed, indicating that the surface tearing and material loss are serious. In contrast, in UAD, as the amplitude increases, the material loss is almost completely suppressed. Consequently, the ultrasonic-assisted micro-hole drilling technology can be an optimal method to overcome the urgent problem of high-quality micro-hole manufacturing.

Instrumented constrained rod casting method and the controlled diffusion solidification (CDS) process were used to study the high susceptibility of the aluminum alloy AA 7068 to hot tearing. A precise analysis of the measured hot-tearing curves is provided considering the casting design and different feeding mechanisms. Scanning electron microscopy was used to study the hot-tear surfaces. It was found that the solidification of the eutectic liquid at the film stage and the phenomenon of solid feeding strongly affects the hot-tear formation. The early formation of an absorbed eutectic layer on the primary phase due to low rate of back-diffusion is proposed to explain the loss of ductility at the film stage. The layer can serve as an efficient substrate for the eutectic nucleation and growth; hence, its formation can advance the eutectic solidification. The isolation of liquid eutectic by its partial solidification results in development of solid-feeding stresses breaking the solid eutectic and provides the required tearing initiators. By increasing the back-diffusion rate, the CDS process avoids formation of the adsorbed solid layer which postpones eutectic solidification thereby mitigating the hot-tearing susceptibility.

Many forming failures such as tearing and wrinkling are encountered during sheet metal forming operations, and it is important for manufacturers to find a quick solution for these failures that hinder the production of a desired part. The theory of inventive problem-solving (TRIZ) is a problem-solving method that considers the patents issued in the past that have been useful in solving problems across a variety of industries. In this paper, TRIZ methodology was utilized to solve the tearing problem occurring during the forming of the lower control arm (automotive suspension part) without altering the desired shape and material of the part. For this purpose, a contradiction matrix was developed and the four different TRIZ principles of segmentation, taking out, the other way around, and parameter change were implemented in four different experiments. Of the conducted experiments, the experiment in which the TRIZ principles of segmentation, taking out, and parameter change were implemented together resolved the problem in a way that was acceptable and feasible for mass production of the lower control arm. WOS:000665698700001 2-s2.0-85116006399

This study examined the microstructural evolution and castability of Al–Mg–Si ternary alloys with varying Si contents. Al–6Mg–xSi alloys (where x = 0, 1, 3, 5, and 7; all compositions in mass pct) were examined, with Al–6 mass pct Mg as a base alloy. The results showed that in the ternary alloys with Si ≤ 3 pct, the solidification process ended with the formation of eutectic α-Al–Mg2Si phases generated by a univariant reaction. However, in the case of ternary alloys with Si > 3 pct, solidification was completed with the formation of α-Al–Mg2Si–Si ternary eutectic phases generated by a three-phase invariant reaction. In addition to the eutectic Mg2Si phases, the primary Mg2Si phases formed in each of the ternary alloys, and the size of both sets of phases increased with increasing Si content. The two-phase eutectic α-Al–Mg2Si nucleated from the primary Mg2Si phases. The inoculated Al–6Mg–1Si alloy had the smallest grain size. Moreover, the grain-refining efficacy of the Al–5Ti–B master alloy in the ternary alloys decreased with increasing Si content in the alloys. Despite the poisoning effect of Si on the potency of TiB2 compounds in the inoculated Al–6Mg–1Si alloy, the grain size of the alloy was slightly smaller than that of the Al–6Mg binary alloy. This resulted from the increasing growth restriction factor (induced by Si addition) of the Al–6Mg–1Si alloy. In terms of the castability, the examined alloys showed different levels of susceptibility to hot tearing. Among the alloys, the ternary Al–6Mg–5Si alloy exhibited the highest susceptibility to hot tearing, whereas the Al–6Mg–7Si exhibited the lowest. The severity of hot tearing initiated by the unraveling of the bifilm was determined by the freezing range, grain size, and the amount of eutectic phases at the end of the solidification process.

Carbon fiber-toughened silicon carbide composite matrix composite (Cf/SiC composite) occupies an important position in the field of aerospace due to its excellent mechanical properties. Because Cf/SiC composite have good high temperature resistance and hardness, machining traditional Cf/SiC composite is a difficult and time-consuming process. In this paper, two-dimensional braided Cf/SiC composite is used as the object, and a new laser-assisted machining orthogonal experiment system for processing Cf/SiC composite is developed by combining laser and conventional machining. The influence of laser-assisted orthogonal micromachining (LAOM) and conventional orthogonal micromachining (COM) input variables on the machining performance of Cf/SiC composite is mainly studied. By comparing the processing characteristics of the workpiece surface roughness, surface micro-topography, etc., the process benefits of laser processing variable changes are analyzed. The orthogonal experiment method is used to analyze the influence of factors such as machining speed, machining depth, and laser power on surface quality. The experiment results showed that the surface quality obtained by LAOM was better than that of COM. The machining depth had the most significant effect on the surface roughness, followed by the laser power, and the machining speed exerted the lowest effect on the surface roughness. Considering the surface quality requirements, the smallest surface roughness of the workpiece was obtained and the surface roughness Sa value was 3.841 μm with the optimal combination: a machining depth of 20 μm, a laser power of 20 w, and a machining speed of 300 mm/s. Microscopic analysis revealed that there were no pits, fiber tearing, pulling out, and other defects on the surface of the LAOM workpiece, and the surface was relatively flat and smooth.

In this paper, biaxial warp-knitted flexible composites (BWFS) were fabricated with high tenacity polyester and PU film. The mechanical properties of the above BWFS samples are tested, including their tensile performance (in 0 °, 45 ° and 90 ° directions), tearing performance (in both 0 ° and 90 ° directions) and stabbing resistance. The results show that the tensile stress firstly decreases and then increases form 0 ° to 90 ° directions and the damage process of composite under uniaxial loading can be divided into three stages. The vertical tearing stress of all BWFS was almost higher than the horizontal tearing stress. In addition, the peak load and deformation displacement of the composites increase with an increase of high tenacity polyester fineness and inserted yarns density in stabbing resistance.

Compared with the conventional drilling, the helical milling has obvious advantages in making holes of carbon fiber-reinforced plastic (CFRP). Nevertheless, the rapid wear of cutting edges readily causes some defects in the outlet holes, such as burrs and tearing. In order to improve the hole-making quality of CFRP, a comparative experimental study on conventional and ultrasonic-assisted bi-directional helical milling of CFRP was carried out. The wear mechanism of the forward and reverse cutting edges was analyzed in the two types of machining, and the change laws of cutting forces and hole wall quality were obtained by different machining means. The experimental results indicated that the flank face of forward and reverse cutting edges was dominated by the abrasive wear mechanism in the ultrasonic-assisted milling. With aggravation of the tool wear, no obvious coating peeled off the forward cutting edge, the reverse cutting edge remained relatively intact, and the wear form of neither cutting edge changed. Furthermore, in the ultrasonic-assisted reverse milling, the axial force and hole diameter deviation were restrained better than in the conventional milling, and especially when the tool wear occurred, the cutting force fluctuation varied slowly. In the ultrasonic-assisted milling, the shear fracture predominated over bending fracture. Meanwhile, the time variation of effective rake angles improved the chip breaking and removing performance of cutters, and thus, the machining quality of hole wall was enhanced obviously.

In this paper, the alumina nitrile rubber was prepared by mechanical blending. The effects of different amount of alumina doping on tensile, tearing and tribological properties of nitrile rubber were studied and analyzed. The results show that the tensile and tear fracture of alumina nitrile rubber is neat, and there are crack propagation and rapid fracture stages, which do not affect the basic fracture mechanism of nitrile rubber. The doping of alumina enhances the matrix strength of nitrile rubber. When 5 g alumina is added, the synergistic load-bearing effect of alumina and nitrile rubber makes the composite have the best wear resistance, and the wear resistance is more obvious at high load and high speed. In friction test, alumina nitrile rubber mainly shows fatigue and adhesive wear.

The hot tearing susceptibility of Mg-1Ca-xSr (x=0, 0.2, 0.4, 0.6, wt.%) alloys was investigated by CRC mold with a contraction force measurement system with a load cell and a temperature monitor. The results showed that the hot tearing susceptibility of Mg-1Ca-xSr alloys significantly improved with increasing of Sr content. Especially in Mg-1Ca-0.6Sr alloy, no visible tear was found on the casting sample. The force dropped and the final force value from the time-force-temperature curve derived from the hot tearing instruments could reflect the hot tearing susceptibility of different alloys. The mechanism of improved hot tearing resistance of Mg-1Ca-xSr alloys was clarified. In addition to susceptible temperature range and eutectic liquid fraction, it is found that the formation tendency of divorced eutectic also plays an important role on the hot tearing behavior of Mg-1Ca-xSr alloys.

Ultrasonic cutting with a disc cutter is an advanced machining method for the high-quality processing of Nomex honeycomb core. The machining quality is influenced by ultrasonic cutting parameters, as well as tool orientations, which are determined by the multi-axis machining requirements and the angle control of the cutting system. However, in existing research, the effect of the disc cutter orientation on the machining quality has not been studied in depth, and practical guidance for the use of disc cutters is lacking. In this work, the inclined ultrasonic cutting process with a disc cutter was analyzed, and cutting experiments with different inclination angles were conducted. The theoretical residual height models of the honeycomb core, as a result of the lead and tilt angles, were established and verified with the results obtained by a linear laser displacement sensor. Research shows that the residual height of the honeycomb core, as a result of the tilt angle, is much larger than that as a result of the lead angle. Furthermore, the tearing of the cell wall on the machined surface was observed, and the effects of the ultrasonic vibration, lead angle, and tilt angle on the tear rate and tear length of the cell wall were studied. Experimental results revealed that ultrasonic vibration can effectively decrease the tearing of the cell wall and improve the machining quality. Changes in the tilt angle have less effect than changes in the lead angle on the tearing of the cell wall. The determination of inclination angles should consider the actual processing requirements for the residual height and the machining quality of the cell wall. This study investigates the influence of the inclination angles of a disc cutter on the machining quality of Nomex honeycomb core in ultrasonic cutting and provides guidelines for machining.

The effect of a low-frequency alternating magnetic field (AMF, 0 A 0 Hz, 5 A 10 Hz, 10 A 10 Hz, 15 A 10 Hz) on the hot tearing susceptibility (HTS) of a magnesium alloy (EV31) was systematically studied using a combination of experiment and numerical simulation. By observing the macroscopic hot cracks in hot joints of the "T" samples, the hot tearing tendency of the samples was analyzed. The HTS of the alloy can be predicted via numerical simulation and the crack susceptibility coefficient (CSC). The microstructure and morphology of the hot tearing zone of EV31 were investigated using scanning electron microscopy (SEM). Results show that increasing the magnetic field strength reduces both the alloy solidification temperature range and the dendrite coherency temperature, which increases the feeding time during solidification and decreases the HTS of the alloy. When the magnetic field parameters are 10 Hz 15 A, the EV31 alloy shows the lowest HTS. The main component of the second phase in the microstructure is Mg12Nd. This study also found that the electromagnetic field can effectively refine the grains, purify the melt, and reduce the oxide content in the melt. The obtained simulation results are consistent with the experimental results.

As a result of frequent food waste and environmental pollution, there has been an increasing demand for the development of packaging materials that intrinsically inhibit and reduce likelihood of non-Newtonian liquids adherence. In this work, inspired from ciliary structures on the leg of water strider, the hierarchical conical array was formed by magnetic field control and laser etching without any mask. Due to the tapered geometry of the cones and the multiscale surface roughness of the array, the droplets would bounce many times after impacting with the superhydrophobic surface (SHS) and roll off. By changing the spaces and apex angles of conical microcolumns the SHS has controlled adhesion, superior self-cleaning property and droplets bounce performance for a variety of non-Newtonian viscous liquids. After suffering from various types of damage including repeated tape tearing, finger touch and folding test, the SHS still maintained excellent superhydrophobic property, which may have potential application as all kinds of packaging interface materials. We demonstrate that the excellent droplets bounce behavior of the hierarchical array enables the efficient and robust prevention of food liquids adhesion.

In order to study the mechanical properties of Recycled Aggregate Concrete-filled Square Steel Tubular (RACFSST) stub columns after fire exposure, a total of 37 specimens were exposed to heating temperatures and cooling phases (including natural cooling and water spray cooling), and the axial compression tests were subsequently conducted. The failure modes, axial load versus deformation curves, and residual bearing capacity of specimens with different cooling methods were obtained. The results show that all specimens suffered steel tube tearing and local buckling. The overall change law of the axial load versus displacement curves was significantly affected by the heating temperature and cooling method, whereas not obviously affected by the replacement ratio of RCA. Compared with natural cooling, the residual bearing capacity of specimens decreased after water spray cooling, with a maximum decrease of 38.17%. A simplified formula for calculating the residual bearing capacity which can take into account the influence of RAC ratio, heating temperature, and cooling method of reclaimed aggregate was proposed.

The fatigue crack propagation (FCP) behavior of FSW welded 7050-T7451 joints was studied using compact tensile specimens. Based on Paris law and three-stage theory of FCP, the FCP rate of joint was obtained by data fitting and calculation. The fracture morphologies at different stages of FCP were characterized by metallography and scanning electron microscopy (SEM). Results showed that the FCP rate in each region for FSW joint was as follows: heat affected zone (HAZ) > weld nugget zone (WNZ) > base metal (BM). In the first stage of FCP, the fracture morphologies of BM and HAZ were mainly tearing ridges and river pattern. There were a small number of dimples on the fracture of BM, but no dimples on the fracture of HAZ. In the second stage of FCP, the fatigue striations of the BM were denser and finer than those in the HAZ, and have dimple fracture characteristics. In the third stage of FCP, dimples still existed in the fracture surface of the BM, and the fatigue striations disappeared. The HAZ was dominated by lamellar tearing and cleavage fracture without dimples. During the three stages of FCP, the fracture morphology of the WNZ in the first and second stages was fine dimple fracture with significant equiaxed deep dimple morphology. In the third stage, the fracture dimple in the WNZ changed from equiaxed deep dimples to tearing dimples.

Hot tearing is a common solidification defect in both continuous cast steels and foundry shaped castings, which has a significant impact on the quality of the final products. It is a complex phenomenon that involves both the thermal and mechanical conditions and chemical element segregation that evolves during casting process. Over several decades, much effort has been invested into improving our understanding of the conditions required for the occurrence of hot tearing and to relate these conditions with casting parameters, like casting speed in continuous cast process, alloy composition, cooling conditions, etc. This review summarizes the results from previous investigations that have focused on the hot tearing phenomenon of steels, including criteria for hot tearing, experimental methods, and several validated models for different testing methods. The factors that influence hot tearing sensitivity are also reviewed and discussed in the present work.

Bonding among fibers is critical to developing a high strength fabric. Chemical adhesive (polyvinyl butyral, abbreviated as PVB) can improve the bonding between fibers to improve yarn strength to the required level. However, retaining the fabric strength after abrasion and washing without the loss of chemical adhesive is challenging. In this study, a novel method has been applied to intra-layer PVB-paste spinning to improve yarn strength. The forming mechanism and PVB flow/fibers compaction model of PVB-paste spun yarn were analyzed. The optimum process parameters of intra-layer PVB-paste spinning combined with orthogonal experiments were established, which maximally increased the binding force between the filament and staple fibers to improve the yarn strength. Moreover, in comparison to original yarn, PVB-paste spun yarn strength can be increased up to 32.3 % in the best case. Therefore, the yarn strength could be improved via intra-layer PVB-paste spinning. Meanwhile, the tearing and breaking strength of PVB-paste fabric were approximately 27.8 % and 7.2 % more than those of cotton fabric, respectively. Additionally, the fabric made by that yarn also maintains good strength performance during abrasion and washing, while also having good hand-feel characteristics. Overall, the successful manufacture of these PVB-paste fabric should promote the development of high-performance fabric.

For roll-bending formation in bow-shaped sheet metal parts, the distance of the traditional roll-forming transverse unit is constant, which often causes corner wrinkles, corner cracks, tearing, springback, and peak longitudinal strain defects throughout the formation process. To solve these shortcomings, this paper proposes an optimized bending angle distribution function to synergize the variable lateral roll distance technique. By parameterizing the abstract function according to the function boundary trajectory, the bending angle of each roll pass is measured; furthermore, the optimal function curve can be obtained through finite element analysis. Then, the roll-bending simulation is conducted, and the forming angle of the sheet metal parts is redistributed to determine the most effective reduction of peak longitudinal strain and transverse roll spacing. The bending angle distribution function aids the variable transverse roll distance technology to execute roll-bending experiments on 3004Al arch parts, ultimately obtaining the optimal roll-bending angle and transverse roll distance. The results of the roll forming simulation, based on the optimized bending angle distribution function and variable transverse roll distance technology, corroborate the experimental results, and good roll forming efficiency and quality are achieved.

A multi-scale approach for simulating hot tearing during the DC casting of aluminum alloys is presented. The novelty of this approach lies in the combination of a macro-scale finite element simulation of the DC casting process with direct prediction of hot tears via a meso-scale multi-physics granular model. This approach is capable of simulating hot tearing initiation, growth, and propagation within a representative volume element of the mushy zone. The change of cooling conditions experienced by the DC cast billet as a result of variations in casting speed as well as non-uniformity of heat extraction from different locations of the billet affect the deformation state, cooling rate, and thermal gradient, which further influence the strain rate, grain size, permeability, and feeding coefficient. Considering all the mentioned parameters, the multi-scale approach emphasizes the fact that hot tearing is a phenomenon resulting from the combination of the tensile deformation and restricted feeding of the mushy zone. The developed hot tearing formation maps identify the locations where hot tearing will occur as predicted by the multi-scale approach for two alloys—AA5182 and AA3104—thus demonstrating the approach’s sensitivity to both processing parameters and alloy composition.

International audience; The stainless clad steel materials (particularly A283-Gr-C hot-rolled to austenitic stainless steel plate SA240 TP 316L) have become widely used in the fabrication of heat exchangers, pressure vessels, and other components owing to their very interesting properties and low production cost. These cladded materials are mostly joined using multi-pass welding techniques. The temperature distribution that supervenes during welding affects the microstructures and the mechanical properties and may generate residual stresses in the heat-affected zone of the welded plates. Since limited experimental data are available in the literature regarding the complex cases of multi-pass welding of cladded steel materials, a thorough experimental study was performed in order to evaluate the temperature distribution on the welded plates. In fact, eight K-type thermocouples were fixed at different distances from the weld centerline in order to record the temperature evolution along longitudinal, transversal, and thickness directions during the welding process. Due to the unavoidable effects of the generated heat fluxes that always follow the welding, several dimensional changes were occurred on the welded plates. In this study, the longitudinal shrinkage and the angular distortion generated during the welding process by the effect of the heat fluxes were investigated. Then, tensile and bending tests were performed in order to check the welded plate reliability. It was found that (i) the welded joint presents a higher mechanical tensile strength than the parent metal and (ii) no separations, fractures, or tearing appear on the weld joint surface after the bending test.

The perforation resistance of fibre metal laminates (FMLs) made of an S-glass fibre reinforced poly-ether-ketone-ketone (GF/PEKK) composite and an aluminium alloy (2024-T3) is investigated. Initial attention is focused on assessing the effect of the processing temperature on the tensile strength of the aluminium alloy. Here, it has shown that the processing cycle results in a reduction of approximately 35% in both the tensile strength and yield strength of the aluminium alloy. A comparison of the quasi-static and dynamic perforation responses of the FMLs highlighted the rate-sensitivity of these laminates, with the perforation energy increasing as the loading rate varies from quasi-static to impact. After testing, the FML specimens were sectioned to highlight the prevailing failure modes. An examination of the cross-sections indicated that the impact energy of the projectile is absorbed through plastic deformation and tearing of the metal layers, delamination between the composite plies and metal layers as well as fibre fracture. Finite element models (FEM), using ABAQUS/Explicit, have been developed to predict the behaviour of the FMLs subjected to dynamic loading. The outputs of the FE models were then validated against the measured experimental force–displacement traces and the observed failure modes. The results of the FE models were in a good agreement with the experimental data, in terms of the initial stiffness, maximum force and maximum displacement, as well as the perforation mechanisms.

The influence of 3.5 wt pct NaCl on the work-hardening response of AA 7004 is investigated through subjecting the tensile data to Kock-Mecking analysis. Due to the exposure to chloride, the decay in the work-hardening rate (−dθ/dσ) increases by ~28 pct when the alloy has GP zones and decreases by ~22 pct when η′/η precipitates are present. In contrast, no significant variation in ultimate tensile strength and elongation values are observed for the alloy, although it suffered embrittlement which results in tearing topography surfaces. Accordingly, −dθ/dσ seems to be a more reliable parameter to assess the environmentally assisted cracking (EAC) susceptibility of the less EAC susceptible AA 7004.

Synthetic, non-degradable packaging materials have become a severe environmental threat, and therefore the demand is growing for environmentally friendly materials for sustainable packaging. This study presents a feasible method of developing a novel, sustainable packaging material using the Arecanut leaf sheath (ALS). CarboxyMethyl Cellulose was coated on the material for improving its mechanical properties. The results were compared with those of polythene: the most commonly used packaging material. The novel material has an areal density of 132.5 g per square meter and 1 mm thickness. The material also possesses a tearing strength of approximately 71% of polythene and exhibits approximately 5% elongation at failure. The bursting strength of the material was found to be three times higher (0.3 kg/cm2) than that of polythene (0.1 kg/cm2). The constitutive behaviour of the material was found to be orthotropic. The breaking force of the material was approximately 70% and 22% of polythene in lengthwise and widthwise directions, respectively. The transmittance of the material varied from 54 to 68% in the visible spectrum. Novel material shows a good thermal stability where initial degradation occurred in the temperature range of 200–375 °C.The tensile behaviour was also numerically modelled using the commercial finite element code LS-DYNA. The predicted stress–strain behaviour of the novel material by the numerical model is in close agreement with experimental results. ALS holds promise as a raw material in the development of transparent, sustainable packaging materials for a wide array of applications.

The hot tearing susceptibilities of an Al–Si based alloy were investigated for hot tearing characteristics. The experimental studies were conducted using a newly developed enhanced constrained rod casting method that enables real-time measurements of the contraction load developed in the casting and the temperature variations during solidification as a function of time. A304 and A380 casting alloys were selected to study hot tearing characteristics at pouring temperatures of 700 °C, 750 °C, and 800 °C. The study showed that hot tearing was not observed in measurement rod of A304 and A380 casting alloys. However, hot tearing was observed in the constrained rods A and B of A380 casting alloy at 750 °C. A304 alloy showed higher resistance to hot tearing at a casting temperature below 750 °C.

Dynamic mechanical properties of thermal aging hydroxyl-terminated polybutadiene (HTPB)-based propellant were tested using split Hopkinson pressure bar (SHPB) under low temperature (− 50 to 25 °C) and high strain rate (800–2000s−1). Relevant test data were obtained. Moreover, microscopic damages of thermal aging HTPB under dynamic conditions were observed through scanning electron microscopy (SEM) and micro computed tomography (CT). The test results demonstrate that the dynamic stress–strain curve of the thermal aging propellant is similar to that of non-aging propellant, and its dynamic mechanical properties show evident temperature and strain rate effects. With the increase in aging time, the dynamic compressive strength of thermal aging propellant increases continuously. Given the same aging time, the dynamic strength of the propellant is negatively related with temperature but positively correlated with strain rate. Moreover, it shows a logarithmic linear relation with strain rate. After low-temperature dynamic loading, the thermal aging propellant mainly presents damages of transgranular fractures, porosity increase, and matrix tearing. Moreover, the thermal aging propellant develops more serious impact-induced damages than the non-aging propellant. Finally, the master curve of the dynamic strength of the thermal aging propellant is obtained based on time–temperature equivalence principle.

Punch–die misalignment is one of the factors that can contribute to drawn cup defects such as thinning and tearing. Deep drawing is a closed-die process, and defects can be identified only after the drawing is finished. In this work, the effect of punch–die misalignment severity on the drawing force and wall thickness distribution of electrolytic zinc-coated steel blank (SECC) was investigated. The stress–strain diagram and forming limit diagram of SECC material was determined and simulated using the Hill’48 model. Two conditions of punch–die misalignment were studied: single-axis and multi-axis misalignment. A high punch–die misalignment severity contributes to the increment in the drawing force. Furthermore, wall thickness distribution becomes non-uniform, and the thinning pattern increases due to the greater misalignment severity. For validation, an experiment was conducted on a universal tensile machine.

During tandem cold rolling mill process, strip tearing reduces production rate, damages the rollers, and consequently decreases efficiency of production. Predicting and postponing of this phenomenon leads to less expensive trial and errors in rolling industries. In this research first, DIN1623 St12 steel which is frequently applied in metal forming industries and also Bao–Wierzbicki ductile damage criterion is selected. Then, six curve fitting methods are employed to calibrate the material and are presented in 2D space of equivalent plastic strain to fracture and stress triaxiality. Finally, the achieved fracture loci are validated by comparing corresponding simulation results with experimental tests and the best curve fitting method with aims of high accuracy for tracking the strip tearing in a tandem cold rolling mill process and fewer numbers of required tests is revealed. Eventually, due to engaging this innovative approach, it is possible to trace the strip tearing in tandem cold rolling mill process by performing only two simple tensile tests. Therefore, it is concluded that strip tearing phenomenon can be precisely predicted in tandem cold rolling mill processes by a special focus on calibration of the Bao–Wierzbicki damage criterion in the range of low positive stress triaxiality which causes less number of needed tests.

The development of new alloys characterized by a high strength-to-weight ratio and low production costs is one of the major objectives of the modern automotive industry with a view to lowering CO2 emissions and obtaining automotive castings that are both lightweight and capable of maintaining their performance under elevated temperature service conditions. The Al-2wt%Cu alloy is one such alloy; it contains 2wt% Cu, 0.05–1wt% Si, 0.4wt% Mg, 0.42wt% Fe, 0.7wt% Mn, and 0.02 wt%Ti (developed by General Motorrs-USA-coded GM220). The low Cu and Si content of the alloy, associated with an acceptable level of tensile strength, make this alloy suitable as a replacement for a number of other alloys such as the 319-type alloys used in engine blocks and cylinder heads. As a new alloy under development, the Al-2wt%Cu alloy has necessitated an in-depth investigation of its castability. Generally, the Al-2wt%Cu-based alloys exhibited higher resistance to hot tearing than 206-based alloys. It was found that an elevated mold temperature is beneficial in reducing the hot tearing susceptibility of the Al-2wt%Cu and 206 alloys in that the hot tearing susceptibility value decreased from 21 to 3, as the mold temperature was increased from 250 to 450 °C. The refinement of the grain structure obtained with Zr-Ti or Ti additions decreased the hot tearing severity as a result of an increase in the number of intergranular liquid films per unit volume and a delay in reaching the coherency point. Increasing the Si content reduced the hot tearing susceptibility of the Al-2wt%Cu alloy considerably; this reduction is attributed to an increase in the volume fraction of eutectic in the structure, and a decrease in the freezing range of the alloy. The addition of Sr caused a deterioration in the hot tearing resistance of the base alloy as a result of the formation of Sr-oxides and an extension of the freezing range of the alloy. It was also observed that α-Fe particles may obstruct the propagation of hot tearing cracks. The 1wt%Si-containing Al-2wt%Cu alloy was judged to be the best composition in view of its low hot tearing susceptibility.

Nomex honeycomb core has been widely applied in aerospace industries due to its superior strength and rigidity. However, the machining defects of honeycomb core can deteriorate the bonding strength between honeycomb core and connective face sheet. This paper investigates the tearing defects formatted in milling process of Nomex honeycomb core. Firstly, a cutting force model is proposed to predict the milling forces under various tool entrance angles. Then, finite element simulation for machining honeycomb wall is conducted to reveal the formation mechanism of tearing defects. The accuracy of the model is verified by a group of experiments under different entrance angles and the relative error is below 25% in 1-direction and 20% in 2-direction. It is found that the formation of tearing defects is closely related to the deformation of honeycomb wall and the component of cutting force in direction parallel to wall. The tool entrance angle can be thus optimized based on the reduction of tearing defects. The optimized entrance angle of double wall is among 40° and 70°.

In this study, aluminium matrix (A6063) composites reinforced with titanium nitride and sugarcane bagasse ash were fabricated using liquid metallurgy technique. Reinforcements were added to a maximum of 10 wt% in aluminium alloy. The composites were then subjected to various mechanical properties study. Microscopic examinations were employed to analyse the distribution of reinforcement and phases in the composites. The tensile and impact test specimen after fracture was exposed to scanning electron microscopy to study the fracture mechanism. The tensile strength, hardness, yield strength and flexural strength of composites increased to a maximum of 29.7%, 31%, 34% and 7.7%, respectively. Ductility and impact strength decreased to a maximum of 47% and 11.5%, respectively. The presence of dimples, shearing, tearing microcracks, pull-out, stress concentration, hillock and particle fracture influenced the tensile and impact fracture mechanisms. Contribution of titanium nitride was higher in influencing the tensile strength, hardness, flexural strength and impact strength than that of bagasse ash.

Mg–Zn–Ca alloy has a good development prospect in biomedical alloy. However, its development is restricted by large hot tearing susceptibility. Herein, the influence of Ca addition on the hot tearing susceptibility (HTS) of Mg-4Zn-xCa-0.3Zr (0.5, 1, 1.5, and 2 wt%) alloys has been studied by using thermal analysis and numerical simulation software, Procast. The “Clyne–Davies” hot tearing prediction model was improved, and Cracking Susceptibility Coefficient (CSC) was recalculated to highlight the physical significance of the model. The hot tearing zone was observed via optical microscopy and scanning electron microscopy, and the phase composition was analyzed with X-ray diffraction. The results of numerical simulations suggest that the Hot Tearing Indicator (HTI) tended to decrease with increase in Ca addition. However, the experimental results reveal that with the increase in Ca addition, the hot tearing susceptibility of the alloys first decreased with Ca addition up to 1.5 wt% and then displayed a slight increase with the addition up to 2.0 wt%. The SEM images and experimental results reveal that the thickness and ability to resist solidification shrinkage stress of the liquid membrane, quantity of the second phases, and feeding ability were all enhanced with the increase in Ca addition, thereby reducing the HTS of Mg-4Zn-XCa-0.3Zr alloys. When the Ca addition reached 2.0 wt%, the brittle calcium-containing phase forms at the grain boundary, which reduces the high-temperature strength of the matrix and the ability to resist the solidification shrinkage stress of the alloy, resulting in an increase in HTS. Therefore, when the Ca addition was 2.0 wt%, the simulation results were different from the experimental results.

Wood fiber/polyethylene composite (WFPEC) is composed of a natural wood fiber and a recyclable polyethylene plastic, which is normally used as an environmental protection composite material. However, better knowledge of chip formation and surface damage mechanism of WFPEC is essential to improve its machinability for extending exterior and interior applications. In this article, machinability of WFPEC was investigated by analyzing the disparity between cutting efficiency and surface quality through a group of orthogonal cutting experiments with change of cutting depth. The chip formation process was recorded by a high-speed camera system with 5000 frames per second. Surface topography was observed by a scanning electron microscope. The results showed that the chip morphology changed from continuous cutting governed by a continuous shearing process under the shallow cutting depth, to a discontinuous cutting governed by plastic fracture under the deep cutting depth ahead of the tool tip. Flattened matrix was the main form of surface topography caused by shallow cutting depth, while matrix-fiber tearing was caused by deep cutting depth. Pullout/fracture and debonding of fibers were related to the fiber orientation angle and the diameter of fiber bundles, but not to the cutting depth. Taken together, the toughness of the workpiece material in the cutting region decreased with the increase in cutting depth. To avoid matrix-fiber tearing, shallow cutting depth should be used during finishing to maintain surface quality. In contrast, pre-cutting can be performed with a deep cutting depth in order to improve the cutting efficiency.

The hot tearing behavior of the double ternary eutectic alloy system, Al-6Mg-xSi (0 to 6.0 wt pct Si) alloys, was evaluated by a constrained rod casting mold equipped with a thermocouple and a load cell connected to a data acquisition system. Experimental results were compared with the results calculated by Scheil’s model using Pandat software to predict the occurrence of hot tearing in Al-6Mg-xSi alloys. The curve of hot tearing susceptibility contained two peaks, which were mainly affected by the double ternary eutectic reactions and the solidification phases evolution. And it agreed with the Kou’s hot tearing index precisely. The types and fractions of solidification phases (Al3Mg2, Mg2Si, and eutectic Si) determined by the addition of Si content changed the freezing range and eutectic liquid fraction greatly. In addition, the types, fractions, sizes, and distributions of solidification phases affected the nucleation, propagation, and healing of hot tear cracks. The maximum contraction force value decreased as the reduction of volume shrinkage coefficient due to the addition of Si content. The drop-in force value on the contraction force curve could indicate the occurrence of hot tearing, and predict the hot tearing susceptibility when considering the shrinkage coefficient.

The fast pressure crash associated with the nonlinear evolution of DTMs is investigated using a three-dimensional toroidal and nonlinear MHD code CLT. Our simulation results indicate that the fast pressure crash is not directly related to the explosive growth of DTM because the explosive growth of the DTM takes place in the earlier nonlinear phase and the fast pressure crash happens in the much later nonlinear stage. It is also found that the explosive growth lasts much longer than the fast pressure crash. At almost the end of the explosive growth phase, the magnetic fields around the magnetic axis become stochastic, and a strong radial flow is generated. The radial flow can effectively transfer the hot plasma around the magnetic axis into the outer cold region and consequently leads to the fast crash of the pressure in the core. As a result, the dependence of the crash time on the resistivity is very weak. It is also found that the geometry of Tokamaks has very weak influence on the fast pressure crash.

Gd has higher solid solubility than Y in Mg, which has a greater influence on the mechanical properties of the alloy, but there is little research on its hot tearing. In this paper, the coupling behavior of solidification and hot tearing of Mg–xZn–2xGd (x = 0.5, 1, 1.5, 2 at.%) alloy was studied, and its micro-mechanism was revealed. It is found that the microstructure of Mg–2xGd–xZn alloy is composed of α-Mg, LPSO and W phase. With the increase of x, α-Mg grain is refined, the second phase content is increased, and the hot tearing susceptibility is decreased. Under the same composition, Gd has a better effect on reducing the hot tearing tendency than Y. Further studies show that with the increase of x, the relative content of residual liquid phase between α-Mg grains increases after crystallization, and its feeding ability to local shrinkage of solid phase is enhanced. In addition, the morphology of LPSO precipitated along the grain boundary is wedged into both sides of α-Mg matrix, which is considered to be helpful to prevent the propagation of hot cracking along the grain boundary, which is another important reason to reduce the hot cracking sensitivity of the alloy.

This research study reports the central slit tearing behaviour of three different varieties of industrial-grade high-strength fabrics, namely (a) Kevlar, (b) Nylon 6, 6, and (c) Polyester, all of these with a special thermoplastic polyurethane (TPU) coating. Tear resistance was evaluated and the tear behaviour was analyzed based on the critical load required for tear initiation and the energy required for tear propagation, by changing slit length and slit orientation. The study revealed that the coated Kevlar fabric has the highest specific tear energy among all the fabric materials, but the Polyester fabric displayed highest tear load and tear energy. This research work also showed that there are three major factors that determine the tear performance of envelope material, namely the yarn tenacity, yarn count, and yarn weaving density/yarn spacing, so the index based on the three factors was proposed for explaining the tearing behaviour. The materials for coating were selected for assessing the performance for inflatable application, so the degree of anisotropy was calculated for the tearing parameters; load, energy, and specific energy for all the coated fabrics. The breaking strengths of three varieties of basic and coated fabrics were evaluated for assessment of the influence of TPU coating.

In the advanced Tokamak magnetic field configuration, the instability of the double tear mode excited by the diamagnetic shear configuration plays an important role. At the same time, due to the fusion reaction and auxiliary heating means, a large number of fast particles will be generated. The existence of fast particles will affect the growth of double tear mode. In the context of resistive magnetic fluids, the role of fast particle specific pressure in the instability of the double tear mode was analyzed, and the CLT-K program was used to simulate the instability of the fast particle specific pressure to the double-tearing mode to explore the physical mechanism of its impact.

Titanium alloy, with superior mechanical properties, is widely used to manufacture key parts in the aerospace industry. Nonetheless, there exist some problems in machining titanium alloy, such as low machining efficiency, serious tool wear, and difficulty to guarantee the surface quality. In this paper, the comparative experimental study is conducted on milling the titanium alloy TC11 with indexable milling cutters and self-propelled rotary milling ones, and the wear process of the two types of cutters is explored to have found how the milling force, chip micro-morphology, and machined surface quality of theirs vary according to milling length. The experimental results indicate that compared with indexable milling cutters, self-propelled rotary milling cutters show relatively minor and slowly increasing cutting forces. Moreover, self-propelled rotary milling cutters show better wear resistance; that is, the flank wear is more evenly distributed along the cutting edge and the wear rate is slower. The two types of cutters both produce serrated chips, but the curling degree of the chips produced by self-propelled rotary milling cutters is comparatively larger than that by indexable milling cutters, and with the increase of milling length, the former produces more regular chip morphology and evener sawtooth distribution. When the cutting edge wear is slight, the machined surface quality by the two types of cutters does not differ a lot. However, with the increase of the milling length, the wear of indexable milling cutters becomes increasingly serious, and the machined surface quality by it becomes a lot worse as some defects occur such as holes and tearing on the workpiece surface. In comparison, the surface roughness of self-propelled rotary milling cutters get worsen slowly.

Carbon fiber reinforced plastic (CFRP) composites are extremely attractive in the manufacturing of structural and functional components in the aircraft manufacturing field due to their outstanding properties, such as good fatigue resistance, high specific stiffness/strength, and good shock absorption. However, because of their inherent anisotropy, low interlamination strength, and abrasive characteristics, CFRP composites are considered difficult-to-cut materials and are prone to generating serious hole defects, such as delamination, tearing, and burrs. The advanced longitudinal–torsional coupled ultrasonic vibration assisted drilling (LTC-UAD) method has a potential application for drilling CFRP composites. At present, LTC-UAD is mainly adopted for drilling metal materials and rarely for CFRP. Therefore, this study analyzes the kinematic characteristics and the influence of feed rate on the drilling performance of LTC-UAD. Experimental results indicate that LTC-UAD can reduce the thrust force by 39% compared to conventional drilling. Furthermore, LTC-UAD can decrease the delamination and burr factors and improve the surface quality of the hole wall. Thus, LTC-UAD is an applicable process method for drilling components made with CFRP composites.

Helical milling, a new machining technology, has obvious advantages in hole making of carbon fiber reinforced plastic (CFRP), and the technology, nonetheless, shows some defects such as hole diameter tolerance and surface damage aggravation caused by fast tool wear. Aiming to improve the hole making quality of CFRP, this paper proposes the bi-directional helical milling strategy, carries out the experimental research on milling CFRP with stepped bi-directional milling cutters, analyzes the wear mechanism of forward and backward cutting edges, and thus obtains the change laws of cutting forces and hole-making quality in different tool wear conditions. The experimental results show that in the initial milling stage, strip-shaped and spoon-shaped wear bands are formed by abrasive wear mechanism on both forward and backward cutting edges; with aggravation of the tool wear, the wear mechanism of forward cutting edge is gradually dominated by the fatigue wear, and subsequently, a large-area coating peels off the tool surface, causing the rapid wear of substrate. Compared with the forward cutting edge, the backward cutting edge produces less and more stable axial cutting force, and causes all the cutting forces to rise more slowly. In comparison with traditional drilling and milling of CFRP, bi-directional hole-making can effectively suppress some defects such as hole diameter shrinking, burrs and tearing, and thus it shows better machining quality.

Mg–2xY–xTM(Zn,Cu,Ni) alloys reinforced with LPSO have outstanding mechanical properties, but there is less research on Mg–2xY–xNi hot tearing sensitivity. Therefore, based on Clyne Davies Model and Newton Baseline Method, the hot tearing tendency of Mg–2xY–xNi alloys with x = 0.5, 1, 1.5, 2.0, 2.5 wt% was quantified, and the tendency was further verified by the tearing evaluation of “T” shaped castings. The results show that the hot tearing susceptibility (HTS) decreases with the increase in x. Especially when x ≥ 1.5 wt%, and the HTS of Mg–Y–Ni alloys is even lower than that of Mg–Y–Zn alloys. The analysis of solidification microstructure evolution reveals that with the increase in x, the grain refinement and equiaxed tendency of α-Mg increases, and the solid fraction increases when dendrites are coherent, and the feeding stage of residual liquid phase between dendrites is shortened, which is an important reason for the decrease in hot tearing tendency. The analysis of phase transformation shows that with the increase in x, the residual liquid phase between α grains increases, which has better feeding effect on solidification, while the precipitation amount of LPSO phase which has coherent relationship with α increases, and its bridging effect on inhibiting grain boundary cracking is enhanced, which is another reason for reducing the HTS.

This study was undertaken to investigate the tensile properties and hot tearing susceptibility of cast Al-Cu alloys containing excess Fe (up to 1.5wt%) and Si (up to 2.5wt%). According to the results, the optimum tensile properties and hot tearing resistance were achieved at Fe/Si mass ratio of 1, where the α-Fe phase was the dominant Fe compound. Increasing the Fe/Si mass ratio above unity increased the amounts of detrimental β-CuFe platelets in the microstructure, deteriorating the tensile properties and hot tearing resistance. Decreasing the mass ratio below unity increased the size and fraction of Si needles and micropores in the microstructure, also impairing the tensile properties and hot tearing resistance. The investigation of hot-torn surfaces revealed that the β-CuFe platelets disrupted the tear healing phenomenon by blocking interdendritic feeding channels, while the a-Fe intermetallics improved the hot tearing resistivity due to their compact morphology and high melting point.

The influence of Nd on the hot tearing susceptibility(HTS) of Mg-4.5Zn-1Y-xNd-0.5Zr (x = 0, 1, 2, 3 wt.%) alloy was systematically studied by using Clyne–Davies model, the Newton baseline method based on the thermal analysis and the “T” hot tearing die with temperature and force testing system. The HTS of the alloy decreased first and then increased with Nd content increase, reaching the minimum value at the Nd content of 2 wt.%. Based on the results of thermal analysis, the solidification path of multi-component alloy was studied, and the evolution of phase precipitation and microstructure was discussed by SEM, EBD and TEM. It was found that the precipitation of W-phase, which has a relatively high precipitation temperature and a certain coherent relationship with the parent phase, and reduced the intergranular hot tearing tendency. The results show that with the increase in Nd content to 2 wt.%, the decrease in HTS was due to α-Mg grain refinement, and the entry of Nd atoms into phase I and phase W, so that the ratio of phase I with low melting point to phase W decreases. When the content reaches 3 wt.%, the reason of HTS decrease was α-Mg grain turn to coarsening and the appearance of another T-phase with much lower melting point than W-phase, i.e., ternary (MgZn)92Nd8 phase. It was considered that the smooth feeding channels caused by fine and uniform α-Mg grains and the high grain boundary bridging strength from the higher precipitation temperature of W-phase with a certain crystallographic relationship to the matrix leads to the lowest HTS of the Mg-4.5Zn-1Y-2Nd-0.5Zr alloy.

In this paper, the finite element tearing and interconnecting (FETI) method and proper orthogonal decomposition-based reduced order model (POD-ROM) are suggested as fast and novel computational approaches for multi-scale and multi-physics analysis. FETI is one of non-overlapping domain decomposition methods, facilitating the parallel computation. POD-ROM reduces the number of degrees of freedom (DoFs) to several representative POD modes which completely describe the behavior of the full order model. The computational time for the analyses using large number of DoFs can be decreased by using the previously mentioned methods. The present FETI-local and POD-ROM are found to reduce computational time significantly in each example.

This paper proposes a novel collision post structure designed to improve the crashworthiness of subway cab cars. The structure provides two innovative features: 1) a simpler connection between the post and the car roof, which gives a more reasonable load transfer path to reduce the stress concentration at the joint; and 2) a stiffness induction design that provides an ideal deformation model to protect the safe space of the cab cars. The novel collision post structure was evaluated with finite element analysis, and a prototype cab car was mechanically tested. The results demonstrate that the deformation response was stable and agreed well with the expected ideal mode. The maximum load was 874.17 kN and the responses remained well above the elastic design load of 334 kN as required by the design specification. In addition, there was no significant tearing failure during the whole test process. Therefore, the novel collision post structure proposed has met the requirements specified in new standard to improve the crashworthiness of subway cab cars. Finally, the energy absorption efficiency and light weight design highlights were also summarized and discussed.

The effects of pouring and mold temperatures on the fluidity and hot tearing susceptibility (HTS) of Al–3.5Si–0.5Mg–0.4Cu alloy were investigated by the spiral mold test and the constrained-rod casting mold test, respectively. Optical microscope (OM) and scanning electron microscope (SEM) were carried out for microstructure observation. The results showed that the flow length (Lf) of Al–3.5Si–0.5Mg–0.4Cu alloy increased with increasing pouring temperature (T) and mold temperature (T0). Moreover, the functional relationship between the fluidity and casting parameters was obtained by fitting the fluidity data as: $$ L_{f} \, = \, 60.9 \, + \, 1082.4\text{[}\Delta T/T - T_{0} \text{]} $$ . The hot tearing mechanism was analyzed by observing the microstructure of the hot crack, and the HTS of the alloy with the mold and pouring temperatures was discussed in detail. According to the research, to achieve a lower hot tearing susceptibility under better fluidity, the suggested pouring and mold temperatures are 740 °C and 200 °C, respectively.