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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.

Geotextile is made of permeable geosynthetic. Geotextile s are formed from synthetic fibers based on polymers that have high mechanical properties in tensile strength, trapezoidal tearing strength, and puncture resistance. Therefore, researchers want to increase the use of Geotextile as an added material in the tensile area of concrete blocks. The test objects used are 9 pieces of 150mm×150mm×600mm beams. The results of the research were that the addition of woven Geotextile s and non-woven Geotextile s on concrete blocks increased, for woven Geotextile s by 21.593% of beams without using Geotextile s and non-woven Geotextile s of 17.058% of beams without using Geotextile s. So the use of Geotextile s on concrete blocks can improve quality because the value of the flexural strength of beams using Geotextile s is greater than beams without using Geotextiles.

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.

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.

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 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.

In this paper, we have studied the influence of resonance magnetic perturbation (RMP) on the double tearing modes induced by asymmetric magnetic perturbation in a 2D geometry based on the MHD model...

Statement of the problem. The goal of this study is to identify the effect of wet surfacing on its wear and tear. The mechanism of influence of transport loading in the presence of moisture and experimental methods of measurement of its influence on wear and tear of the top layer of asphalt concrete are discussed. Results. The contribution of the presence of moisture in the upper layer of the pavement to its wear and tear in the form of track formation was identified, and the hydrodynamic effect of water in the micropores of the pavement was investigated. Experimental data on the values of water pressure in the pores of the asphalt-concrete pavement in the moistened state under the action of the wheels of the moving traffic flow were obtained. Therefore it became possible to identify the maximum values of the pressure effect, the depth of penetration of the fluid pressure front and its effect on the destruction of the surfacing.Conclusions. The analysis of the data showed not only the presence of brittle fracture, but also the impact of moisture moving in the pores of asphalt concrete, exceeding its structural strength. Using experimental data, regression dependences of the wear and tear value on the standard flow parameters were obtained. For the operated surfacings regression dependence enables one to predict the size of wear and tear for the whole life cycle of the road.

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.

Aim: To investigate the relationship between the degree of tearing in the rotator cuff tendons and the subacromial region volume using the proton-density weighted Sampling Perfection with Application optimized Contrasts using different flip angle Evolution technique and the contribution of this technique to shoulder magnetic resonance imaging. Material and methods: A total of 125 patients who underwent shoulder magnetic resonance imaging for shoulder pain between January 2016 and December 2016 were included in this single-center, retrospective study. Rotator cuff tendon injury grading was performed using coronal plane 2D short tau inversion recovery T2-weighted sequences (grades 1–4). Subacromial region volume was calculated from PD-weighted 3D SPACE sequence images in sagittal oblique plane. The relationship between rotator cuff tears and subacromial region volumes was evaluated using Pearson’s correlation analysis. The measurements were made at different times by two independent radiologists. Results: There was a strong negative correlation between the grade of RC tendon tear and subacromial volume (p Conclusion: Shoulder magnetic resonance imaging with high-contrast resolution can be obtained by the Sampling Perfection with Application optimized Contrasts using different flip angle Evolution technique. The degree of rotator cuff tendon tear, which is a cause of shoulder pain, is associated with the subacromial region volume. Using the Sampling Perfection with Application optimized Contrasts using different flip angle Evolution technique can also easily reveal the cause of the damage.

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.

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.

Different types of rotor-stator and jet-impingement refining equipment are used depending on the methods of production of fibre semi-finished products and on the initial state of raw materials. This article examines various refining modes for jet-impingement devices and their influence on the physical and mechanical properties of the processed material. Main design parameters that affect the refining process in this type of plant were determined. It was shown that the time required to refine a fibre mass using this plant depends on the jet flow rate (from the nozzle to the barrier), i.e. as the jet flow rate increases, the time required to refine the fibre mass decreases. A dimensionless machine parameter was obtained that characterises the effectiveness of the refining process and the design of jet-impingement refining plants. Using the dimensional method, a functional dependence was observed of breaking length, bursting strength, folding strength, and tearing strength on the machine complex parameter. The numerical value of the machine complex parameter was determined, depending on refining duration.

AA3003 aluminum alloy made from raw scrap materials that have the advantage of economical use, but hottearing often occurs in the product billets of the direct chill casting process. This study used ANOVA analysis method for determination of chemical composition of AA3003 aluminum billet products to show influence of chemical composition on hot-tearing ability. The evaluation of the microstructure and chemical composition distribution of the elements by optical and scanning electron microscopes combined with energy dispersive spectroscopy showed the existence of impurities such as Cu, Zn, Fe, Pb exceeding the allowable limit in aluminum billets, especially at grain boundary, which can be the main reason for the hot-tearing of cast aluminum billets.

The subject matter of the article is a comparative analysis of indicators of strength and elasticity of textile materials of the main parachute canopy before and after long-term storage. A simplified approach proposed by N. A. Lobanov and P.O. Fomichov was used, the coefficients of degradation of the strength characteristics of the textile materials of the main parachute of the D-5 landing parachute system of series 2 after its long-term storage were experimentally determined. These coefficients are defined as the ratio of the strength characteristics of individual elements of the parachute system in the design sections after the operation or long-term storage to their initial value adopted in the design of the parachute. The goal is to obtain an array of data to assess the state of the physical and mechanical characteristics of the main parachute materials. It is known that in the process of long-term storage there is a deterioration (degradation) of the strength characteristics of the strongest elements of the frame of the parachute canopy, lines, canopy fabrics, reinforcing tapes, etc. Further operation beyond the established period while maintaining sufficient safety factors is possible only with the availability of modern data. Tasks: to develop and test a method of sampling materials, experimentally determine the characteristics of materials, choose an effective algorithm for calculating safety factors. The following methods and equipment were used. The actual value of the indicators was established by destructive strength measurements. The methodology for preparing test samples of D-5 series 2 landing parachute systems, taking point and elementary samples of textile materials of individual elements of the parachute system in design sections for laboratory research to determine mechanical characteristics (strength, elongation, and air permeability) has been improved. The tearing machine is equipped with specialized clamping devices. The batch size was 25 parachute systems. The breaking load and the relative elongation were measured for slings and braids, for fabric - along the warp and weft, a total of 1250 elementary samples. Degradation coefficients were calculated. The array of empirical data was processed by mathematical and statistical methods of the Descriptive Statistics software package from the add-in of the MS EXCEL Analysis Package. The following results were obtained. In terms of breaking load, the fabric of the main parachute canopy slightly (up to 3 percent) exceeds the standard value. The elastic characteristics of the fabric fully meet the requirements - exceeding 1 ÷ 4 percent. During storage, the slings of the main parachute lost up to 21% in strength, but at the same time retained their elastic properties - exceeding up to 3 times. The tapes have satisfactory strength characteristics (exceeding from 3 to 12 percent), in terms of elongation at break, they have lost from 15 to 25 percent. Conclusions. The novelty of the results obtained is as follows: for the first time, the strength characteristics were measured and evaluated in the design sections of the fabric, reinforcing tapes of the power frame of the canopy and lines of the main parachute of the D-5 landing parachute system of series 2 on a large sample of 25 parachutes; it is shown that the obtained data will be correct for all parachute systems produced in 1973-1974.

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.