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A criterion based on solidification microstructure was proposed to precisely predict the hot tearing behavior of cast alloys, which takes into account the effects of both mechanical and nonmechanical factors. This criterion focuses on the events occurring at the grain boundary, which are determined by the thermal contraction, solidification shrinkage, grain growing and liquid feeding. This criterion responds to a series of factors that affect hot tearing, such as alloy composition, mold design, casting process and microstructure. Its credibility has been validated by studying the hot tearing behavior of Mg-Ce alloys. In conformity with the experimental results, this criterion predicted decrease in the number of rods occurring hot tearing with increasing cerium content. A simplified criterion was derived and validated by Mg-Ce (equiaxed grain) and Mg-Al (columnar grain) alloy systems, which is suitable for the case where the eutectic liquid fraction is low and the liquid feeding can be ignored. In addition, a hot tearing index for equiaxed grains was proposed, that is, | d T / d ( f s 1 / 3 ) | near ( f s ) 1 / 3 = 1 , and its prediction results were consistent with the hot tearing susceptibility calculated from the experimental results.

Abrasive waterjet (AWJ) has a significant impact on the dimensional accuracy and machining damage of Cf/SiC composites. Thus, this paper aims to investigate the hole characteristics and formation mechanisms of surface damages (e.g. crack damage, tearing damage, delamination damage and burr damage). The results show that the diameters of hole entrance and hole exit varies with the traverse speed, jet pressure, standoff distance, and abrasive flow rate within certain parameters range. The over-machined phenomenon has the greatest impact on the hole dimensional accuracy, which can be effectively enhanced by improving the jet trajectory. The formation mechanisms of various damages are also obtained. These results will guide realizing high-precision and low-damage hole machining for ceramic matrix composite material.

Aluminum-copper (Al-Cu) alloy B206 is a high strength and ductile alloy showing promise for use in automotive suspension components. Incorporation of lightweight B206 alloy in automotive suspension components may significantly reduce overall vehicle weight and increase the vehicle’s fuel efficiency. However, one of the major factors inhibiting the use of B206 is its high susceptibility to hot tearing during casting. Hot tearing is a complex phenomenon attributed to alloy solidification, microstructure and stress/strain development within a casting. Numerous methods (e.g. preheating of mold, grain refinement, elimination of sharp corners in a component) help to reduce the occurrence of hot tears in castings, but the underlying mechanisms responsible for hot tearing remain ambiguous. This research aims to advance the understanding of the mechanisms responsible for hot tearing in B206 Al alloy. In this research, the conditions associated with the formation of hot tears in B206 were investigated via ex situ and in situ methods. Titanium was added in three levels (i.e. unrefined, 0.02 and 0.05 wt%) to investigate the effect of grain refinement on hot tearing. Ex situ neutron diffraction strain mapping was carried out on the three B206 castings to determine casting strain and stress. Further, in situ techniques were used to establish the onset temperature and solid fraction of hot tearing in B206 and to improve the understanding of microstructure development in B206. The results indicate that titanium additions had a significant impact on the hot tearing susceptibility of B206, by effectively reducing grain size and transforming grain morphology from coarse dendrites to fine globular grains. Further, thermal analysis suggested that grain refinement delayed the onset of dendrite coherency in B206 and therefore enhanced the duration of bulk liquid metal feeding for the refined casting conditions. As a result, the interactive effects of such factors resulted in a more uniform distribution of strain, and subsequent higher resistance to hot tearing for the grain refined castings. Finally, in situ analysis determined the onset solid fraction of hot tearing in B206 and provided an understanding of the role of microstructure on hot tearing in B206.

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.

Mechanical and metallurgical behavior of double-sided friction stir welded (DS-FSW) joints of 6 mm thick magnesium alloy (AZ31B) plates, under 0° (Joint W1) and 2° (Joint W2) tool tilt angle, using scrolled shoulder and screwed pin tool were investigated for the first time. Joint fabrication using tool rotational speed of 800 rpm and welding speed of 50 mm/min resulted in tunnel defect in W1 joint and defect free W2 joint. The tensile test results show the joint efficiency of 74% for W1 joint and 87% for W2 joint. The defect free micro tensile samples extracted from first pass (FP), second pass (SP) and overlap region (OZ) of both the welds shows higher degree of grain refinement. Also, microhardness in stir zone (SZ), thermo-mechanically affected zone (TMAZ) and heat-affected zone (HAZ) of W2 joint is high compared to W1 joint. These metallurgical enhancements in each zone of 2° tilt angle joint led to the remarkable improvement in joint efficiency of FP-2 (80%), OZ-2 (71%) and SP-2 (91%) tensile specimens compared to FP-1 (76%), OZ-1 (63%) and SP-1 (67%) for W1 welded joint. Significant improvement by 26%, 19% and 32% and in percentage elongation was observed in the first pass, overlap region and second pass respectively for W2 joint over W1 joint. Scanning electron microscopy (SEM) characterization revealed ductile and shear fracture modes, wherein, larger area fraction of dimpled morphology and tearing ridges was observed for the macro and micro tensile specimens of W2 joint.

In this study, 6802-T6 alloy plates were welded using tools with different pin lengths. Different depths of incomplete penetration defects, including kissing bond (K) defect and remain joint surface (R) defect, were obtained. Mechanical fracture and kernel average misorientation (KAM) maps indicated that joint root tearing caused K defect during the friction stir welding (FSW) process. The critical value for incomplete penetration geometry appeared to be a depth of 0.4 mm. Within this interval, the ultimate tensile strength of the joint (thickness of 3 mm) was more than 224 MPa, and the fatigue strength exceeded 70 MPa at 107 cycles.

Shear assisted processing and extrusion (ShAPE) was used to extrude aluminum alloy 7075 tubing at speeds up to 12.2 m/min without surface tearing. This work presents the first experimental evidence for high-speed extrusion of 7075, which improves upon conventional extrusion where 2.0 m/min is the limit. The increased speed is primarily attributed to more extensive shear deformation, compared to conventional extrusion, which results in a high density of low angle grain boundaries that facilitate continued deformation and delay the onset of surface tearing. Mechanical testing after heat treating to the T6 condition provided an ultimate tensile strength of 565.3 ± 4.6 MPa, yield strength of 495.7 ± 8.7 MPa, and elongation of 16.4 ± 1.0%. Strength values exceed the ASTM International minimum standard and are on par with American Society for Metals (ASM) typical values, while elongation was substantially improved compared to 7 and 11% for the ASTM and ASM values respectively. It was observed that low temperature extrusion at 341 °C and 40 rpm gave superior material properties in the T6 condition compared to high temperature extrusion at 441 °C and 120 rpm because of variances in nanoscale second phase size and distribution.

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.

Longer and stronger; stiff but not brittle Hydrogels are highly water-swollen, cross-linked polymers. Although they can be highly deformed, they tend to be weak, and methods to strengthen or toughen them tend to reduce stretchability. Two papers now report strategies to create tough but deformable hydrogels (see the Perspective by Bosnjak and Silberstein). Wang et al . introduced a toughening mechanism by storing releasable extra chain length in the stiff part of a double-network hydrogel. A high applied force triggered the opening of cycling strands that were only activated at high chain extension. Kim et al . synthesized acrylamide gels in which dense entanglements could be achieved by using unusually low amounts of water, cross-linker, and initiator during the synthesis. This approach improves the mechanical strength in solid form while also improving the wear resistance once swollen as a hydrogel. —MSL

This study conducts alternative-basic-angle trapezoidal tearing and single-edge notch tearing tests on a polytetrafluoroethylene coated woven fabric, where the two methods are related through the basic angle of a trapezoid. The tearing process and failure modes are carefully examined, and load–displacement curves and tearing strength are analyzed. The tearing process comprises three stages, which are distinguished photographically or in different load–displacement curve sections. Corresponding to these stages, failure modes can be classified into three parts with varying extension directions. The effect of the basic angle is clearly illustrated. As the angle increases, three stages and parts appear in sequence; the tearing strength increases, but the larger one changes from weft to warp. The relationship between the tearing process and tearing strength is described. The three stages correspond to the increase in tearing strength, occurrence of the maximum tearing strength, and failure. Because the single-edge notch tearing method is more complex and important, it is the method that is studied mainly. Digital image correlation equipment is used to observe the strain distribution at the crack section. Moreover, the applications of four frequently used models are investigated. The results indicate that Thiele’s empirical formula offers the best simulation among the three tearing strength prediction models, and the theoretical stress distribution model also provides good simulation. Furthermore, a numerical simulation is conducted. The critical tearing strength and load–displacement curves before tearing initiates acquired through the simulation and test agree well. All results may provide basic data for future improvements in design theories.

This study presents an experimental and analytical investigation on central crack tearing properties of PTFE coated fabric. Firstly, tearing tests under uniaxial tension load were carried out to investigate the influence of crack length and crack orientation on tearing properties of PTFE coated fabric. Tear failure process was carefully recorded and two types of failure modes can be characterized, i.e. progressive failure and brutal failure. The effect of initial crack length and orientation on tearing residual strength (TRS) can be attributed to the numbers of the cut yarns, which can be represented by the equivalent crack length. Secondly, the available TRS models are summarized and discussed in detail. It is found that these models can be classified into two types, i.e. fracture-mechanic-based models and stress-field-based models. By comparing the prediction results with test data, these models present to be only valid for small crack conditions, and the stress-field-based model shows better accuracy.

The load-bearing capacity of a CC(T) specimen (Center-Cracked Tension) in the ductile fracture regime is usually controlled by plastic collapse. If the material’s tearing resistance is sufficiently low, the load-bearing capacity can drop below the plastic collapse value. Here, a recently developed simple fracture mechanics-based Charpy-V impact energy criterion for plastic collapse was used to provide a best estimate assessment of the CC(T) specimen load-bearing capacity.

The viability of novel coextruded, fluoropolymer-free backsheets for photovoltaic (PV) modules has been questioned as a result of a large number of early-life backsheet failures in PV installations containing one of the earliest co-extruded polyamide (PA)-based backsheet to reach the market, “AAA.” New PV reliability testing protocols have been recently developed and applied to backsheets to reproduce failures observed in the field and evaluate the durability of novel backsheet materials and designs prior to commercialization. A new co-extruded PA-based backsheet was tested using combined-accelerated stress testing (C-AST) and demonstrated a greater lifetime than AAA, and some other fluoropolymer-based backsheets such as polyvinylidene fluoride. The improved PA-based backsheet also eventually failed by through-thickness cracking. Using surface and bulk material characterization techniques, we performed a comprehensive study of material properties before and after the stress testing. Aging of the backsheet resulted in an increase of surface roughness by erosion of the outer PA layer. However the failure is more likely related to an increase in crystallinity of the polyolefin core layer reducing the backsheet tearing energy. The analysis can ultimately inform on the specific weaknesses of the materials so that the manufacturer can improve the backsheet design to extend its lifetime.

Objective: Aluminium and its alloys components are used in aero and space industries where in many cases trioboloading prevails. In space application, in addition to triboloading, the components should also perform in the absence of atmosphere. In the present investigation, attempted has been made to simulate the field conditions in the laboratory by sliding Al6061 alloy pin of different diameters in a vacuum at different temperatures using a vertically configured pin-on-disc test rig. Method: The pin diameters were 2, 4, and 6mm and the testing temperatures were 373, 473, and 573K. The normal contact pressure was 0.625MPa and the sliding speed was 0.5ms-1 and both were constant throughout the experiment. The coefficient of friction was monitored using a PC and the worn pin surface was studied in scanning-electronmicroscope. Findings: The result showed that the coefficient of friction at sliding temperatures 373 and 473K was found to be dependent on apparent contact area i.e., pin diameters 2, 4, and 6mm. The coefficient of friction was found to be 3.27 and 2.69 for pin diameter 2mm at temperature 373 and 473K whereas the coefficient of friction was of the range 1.36 to 0.33 for the pin of diameter 4 and 6mm. The scanning-electron-microscopic study revealed uniform plastic deformation for pin diameter of 2mm and non-uniform plastic deformation accompanied with abrasion extrusion phenomenon for the pin of diameters 4 and 6mm. The coefficient of friction at sliding temperature 573K was found to be insensitive to the apparent contact area. The coefficient of friction was in the range of 1.24 to 2.30. The SEM study revealed a large scale of non-uniform plastic deformation accompanied by abrasion, tearing of ridges, extrusion of both ridges, and entrapped wear debris. Novelty: It is a generic study for understanding the response of aluminium for tribo loading which. Keywords: Pin on Disc (POD); Scanning Electron Microscope (SEM); High Temperature; Vacuum; Coefficient of Friction; Al6061 Aluminium Alloy 1

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.

The article examines existing works considering the process of tearing of flax fibre, specifically fibrous matrix and linkages within it. In particular authors point out the necessity of taking into account the destruction of individual fibres during deformation and tearing process. The end result of this analysis is a multipart mechanical model allowing for various effects that may take place during the said process. This model is implemented in software and used to model the behaviour of several strands of fibre of varying quality. The results match the observed behaviour of actual samples with similar properties, which allows using the model presented to estimate the effect various properties of flax fibre have on its tensile strength.

Lightweight sandwich structures are used in the aircraft industry because of their high strength-to-weight and stiffness-to-weight ratios. Structural components are often subjected to edge loads in compression or tension. The sandwich structure under the edge compression load exhibits excellent compression capacity. On the contrary of loading under flatwise compression, the sandwich under edge compression undergoes drastic tearing and fracture. The current study is based on experimental work on sandwich-structures made of carbon fiber and natural fiber reinforced face sheets with different core materials. The natural fiber (hemp) is highlighted in the current study to improve the fracture resistance of skins. The hemp-skin demonstrates comparable compression properties to those of carbon fiber under edge compressive load. The skin from hemp has great fracture resistance while the carbon one experienced dramatic fracture, tearing, and delamination. This outcome of the current study, in addition to the lightweight, low- cost ease handling, simple manufacturing, and eco-friendship make the hemp a competitive industrial material in aerospace applications. More details about the manufacturing and the failure modes are discussed as well.

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.

In this study, 40CrMnSiB steel cylindrical shells were tempered at 350, 500 and 600 °C to study the effect of tempering temperature on the dynamic process of expansion and fracture of the metal shell. A mid-explosion recovery experiment for the metal cylinder under internal explosive loading was designed, and the wreckage of the casings at the intermediate phase was obtained. The effects of different tempering temperatures on the macroscopic and microscopic fracture characteristics of 40CrMnSiB steel were studied. The influence of tempering temperatures on the fracture characteristic parameters of the recovered wreckage were measured and analyzed, including the circumferential divide size, the thickness and the number of the circumferential divisions. The results show that as the tempering temperature was increased from 350 to 600 °C, at first, the degree of fragmentation and the fracture characteristic parameters of the recovered wreckage changed significantly and then became essentially consistent. Scanning electron microscopy analysis revealed flow-like structure characteristics caused by adiabatic shear on different fracture surfaces. At the detonation initiation end of the casing, fracturing was formed by tearing along the crack, which existed a distance from the initiation end and propagated along the axis direction. In contrast, the fracturing near the middle position consists of a plurality of radial shear fracture units. The amount of alloy carbide that was precipitated during the tempering process increased continuously with tempering temperature, leading to an increasing number of spherical carbide particles scattered around the fracture surface.

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.

Polyacrylamide is widely employed in constructing functional hydrogels. However, the volume expansion of this hydrogel in water weakens its mechanical properties and restricts its application. Herein, we report a strategy to convert the swollen and weak polyacrylamide/carboxymethyl chitosan hydrogel into a strong and tough one by hydrolysis in acid solution with an elevated temperature. The obtained hydrolyzed hydrogels possess a high strength, toughness, and tearing fracture energy of 5.9 MPa, 22 MJ/m3 and 7517 J/m2, which are 254, 535 and 186 times higher than those of the original swollen one, respectively. In addition, the gels demonstrate low residual strain and rapid self-recovery abilities. Moreover, the gels have good shape memory behavior controlled by temperature. Furthermore, the gels can be worked as strain sensors with a broad strain window, high sensitivity, excellent linear response, and great durability in monitoring human motions after immersing treatment in a normal saline solution. This work provides a new method for preparing the stretchable and tough polyacrylamide-based hydrogels used in the areas of soft actuators and flexible electronics.

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.

Tearing strength is one of the important quality items of finished woven fabrics. It refers to the rupture of a fabric progressively along a line thread by thread. Tearing strength mainly depends on fibre, yarn and fabric characteristics along with mechanical and chemical finishing treatments given to the fabric. From an industry point of view, studying this fabric characteristic is an essential and urgent step because it reflects the endurance extent of the end textile structure. The main objective of this investigation is to examine the effect of twist multiplier (4.1, 4.4 and 4.7) on weft/warp tear strengths for fabric samples of cotton/polyester blend (50:50) using carded and combed spun yarns. In addition, three weft densities being 18, 22 and 25 were also applied. Results exhibited that the weft/warp tearing strengths are negatively responded to the increase of twist multiplier and weft density for the two spinning systems. In some cases, the weft-way and warp-way warp tearing strengths may be decreased with increasing twist multiplier to a certain extent and then slightly decreased or constant. On the other hand, it is observed that weft/warp tearing strength values for the fabrics made of combed spun yarns were very close to their corresponding values for carded spun yarns under most tested treatments.

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.

This paper presents a J - integral - tearing modulus analysis for thick plates containing uniform through cracks and subjected to biaxial bending stresses. The solutions are derived for various crack length ratios and applied stress conditions. They are useful for predicting stability of crack propagation in plates with limited plasticity in the vicinity of crack tip. The results are then applied to a carbon steel plate to predict the onset of crack growth instability. Similar applications may be made for other materials, plate geometry and stress conditions.

Tape-based discontinuous composite is a relatively new type of composite material that offers improved mechanical properties for similar process-ability compared to Sheet Moulding Compound or Bulk ...

Pulsed laser welding was used to join ultra thin Inconel 718 alloy foils whose thickness was 0.2 mm. A fixture was designed to obtain the edge joint. The joint geometry and hot cracking were both observed on the cross sections. The relationship between the height, width of the joint and the energy density were fitted as linear functions. The effect of heat input on the hot cracking in the edge joint was obtained. It was shown that a hot cracking occurred during the solidification of the molten metal under laser heating. The crack initiated at the gap between the foil pair and propagated along the Laves phase with low melting point. The crack length could be reduced by applying low heat input. Tearing tests were conducted to evaluate the influence of the cracking on the mechanical performance of edge joints. There existed two failure modes for the edge joint under a tear loading. When the crack length exceeds 106.9 μm the hot crack starts to propagate and the tear loading decreases with crack length increasing. A finite element model was established to simulate the stress evolution during the cooling stage. The main reason of crack initiation and propagation were both presented.

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.

Most of the cracks in the rock masses are in a three-dimensional (3D) state, and it is always a hot topic to reveal the mechanical mechanism of 3D crack growth. In this paper, the research on the growth behavior of 3D crack is performed through laboratory experiments and numerical simulations. Cement samples with different angles of 3D crack are prepared, and the uniaxial compression experiment is carried out. The results indicate that initiation of preexisting crack with an angle of 45° is easier and shear failure characteristics of corresponding samples are obvious. Through theoretical analysis, the preexisting crack starts to grow at the end of the short axis, along the short axis end to the long axis end of the preexisting crack, the shear effect decreases gradually, and the tearing effect increases gradually. Combined with numerical simulation, the experimental and analysis results are verified, and the preexisting crack growth process is presented. The growth direction of the preexisting crack changes from perpendicular to the crack surface to parallel principal stress direction, and the maximum growth length can reach 1.2 times the minor axis radius of the preexisting crack. The research results can provide an important theoretical basis for revealing the evolution process of the cracks in rock masses.

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.

To study the removal mechanism and damage behavior during the machining of ceramic particle-reinforced metal matrix composites, a finite element model (FEM) comprehensively considering the distribution and shape of the particles and the damage behavior of ceramic particles is established. Corresponding experiments are conducted to demonstrate the reliability of FEM. The results demonstrate that chips are easy to separate where the particles gather. The stress concentration is serious at the edges and corners of the particles. The cutting and thrust force, subsurface damage, surface roughness and maximum profile peak-valley height increase with the increase of depth of cut. Voids, particle fracture, particle peeling off, matrix tearing and interface failure are the main surface defects. Moreover, according to the failure mode and mechanism of ceramic particles, the positional relationships between the ceramic particles and the tool are divided into three categories: the particle is below, on and above the cutting path.

Recently, much interest has been attracted in the graphene-assembled hollow nanospheres (GAHNs) because of outstanding multi-functional properties. This paper systematically explores the compressive mechanical behaviors and gas bearing capability of GAHNs by a coarse-grained molecular dynamics (CGMD) simulation combining with in-situ compressive test. It was found that the GAHNs possess excellent compressive elasticity (experimentally recoverable strain can reach ∼ 58%). Under large compressive strain (>90%), the GAHNs also display obvious plastic deformation owing to inter-layer slippage between graphene nanosheets. In addition, the morphology of force measurement tip (FMT) plays critical roles on the compressive failure modes of GAHNs. When FMT is sharp, it can pierce through the shell of GAHN, whereas the blunt one compels GAHN to collapse. The thermal expansion process of GAHNs was investigated by CGMD simulation. With the increase of ambient temperature, the internal pressure of GAHN increased until a crack appears. To further understand this expansion failure, an in-situ scratching experiment was designed and the tearing strength of shell of GAHN was estimated to be ∼748 MPa. This work provides an in-depth understanding on intrinsic mechanical properties of GAHNs and broadens their potential applications.

The research deals with the effect of industrial materials and acids on the natural properties of paper. In it, the fibrous and chemical composition of the paper was addressed and the mechanical properties of the paper were studied in terms of tensile strength, folding strength, force of tearing, as well as the study of physical properties in terms of density, degree of thickness and weight, as well as optical properties in terms of the degree of gloss and opacity, as well as the chemical properties in terms of the degree of viscosity and the degree of polymerization.- Additives during the manufacturing process (chemicals - natural materials) and their effect on the manuscript.- Treatment methods and materials.- Conditions during formation.- Drying and polishing.The impact of these substances and treatments on the age of the manuscript and how to avoid the impact of these substances in the future, as well as how to deal with the damage caused by them and the ways in which they are treated, were studied.

Steel ingot with a large height-to-diameter ratio is utilized to produce multiple products by one stock in practice. Water cooling is a usual way to enhance production efficiency. However, the combination of the two factors will generate internal defects, such as shrinkage porosity and hot crack. The characteristic of internal shrinkage crack in a 10 t water-cooled steel ingot with a large height-to-diameter ratio was examined by an ultrasonic test. A slice was sectioned from the ingot middle part where billets containing star-like crack were further extracted. The billets were examined by X-ray high energy industrial CT, and the compactness was reconstructed in three dimensions. Microstructure near the crack was observed using scanning electron microscopy, and the solidification process and grain size were studied by high temperature confocal microscopy. Moreover, thermomechanical simulation and post-processing were carried out to analyze the formation of shrinkage porosity and hot crack. A new criterion considering mushy zone mechanical behavior in brittle temperature as well as grain size distribution was proposed to evaluate hot cracking potential in the ingot. The results show that a deep shrinkage porosity band easily forms in the center line of such an ingot with a large height-to-diameter ratio, and water-cooling further generates excessive tensile stress tearing the liquid films around the porosities. Then, hot cracks begin to propagate along grain boundaries. The grain size in the upper and center of the ingot is large, which leads to an inverted cone shape defects zone in the ingot center.

In this study, detailed uniaxial in-plane tearing tests including uniaxial central, single-edge notched, and trapezoidal tearing tests of a type of polyvinylchloride (PVC)-coated polyester fiber fabric were conducted. Two types of tearing failure modes, brutal and progressive, were examined. In addition to differences in the descending sections of the stress–displacement curves and the membrane surface morphology near the crack, it was found that the uniaxial central tearing test could be replaced by the corresponding single-edge notched tearing test to minimize the usage of test materials. The configuration of the single-edge notched specimen, including the gauge length and width, was investigated to determine the conditions under which the tearing resistance of the practically nearly infinite membrane surface can be studied with finite-size specimens. To obtain the fracture toughness GIC, which characterizes the ability of materials to prevent crack growth, a theoretical method and two test methods were introduced. After comparing the methods, the test method based on the area of the parallelogram obtained from the zigzag wave in the descending section of the load–displacement curves was proved to be superior. The value of GIC obtained with this simple test method was relatively stable, and it could be used to evaluate the tearing resistance and calculate the tearing strength of the coated fabrics.

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.

In order to understand the fracture behavior of the fractured tube of the ammonium pipeline in the fertilizer production system. it is necessary to take into considerauon the interrelation among nucrostructure, development of voids and the mechanical behavior of the material from which the tube is made. A study of the influence of microstructures parameters on fracture toughness of the tube material (Nickel-Iron Chromium alloy) has been made. Using the J integral concept. J-resistance curves have been obtained and the influence of strain hardening on fracture toughness has been evaluated. Hence, the tearing instability Concept was applied to investigate the fracture Process. The relationship between critical Stress intensity factor and the microstructural parameters has been taken into account Ductile fracture occuring by the formulation growth and coalescence of voids around the inclusions was described. In addition micro-fractographic culmination has been carried out to establish a possible corrclation between the mechanical properties and the micro mechanisms of fracture.