Rubber is an important material in mechanical engineering industries. Rubber sealing materials play a key role in many mechanical instruments, and aging of rubber seals may cause unpredictable failures or even huge losses. Hence, aging research of rubber sealing materials are attracting great attentions. The aging research progress of rubber sealing materials is reviewed, including aging behavior and mechanism, effects of stress and chemical media on aging, lifetime evaluation indexes and prediction, and aging analysis techniques. The existing problems in aging research of rubber sealing materials are discussed. Future research perspectives are proposed, including studies on accelerated aging methods, aging mechanism, correlation between accelerated aging and natural aging of rubber seals, and so on.

With the continuous development of intelligent society, piezoelectric sensors are increasingly used. The types, structures, measurement principles and application scenarios of piezoelectric sensors are described. The research progress on sensitive element materials is reviewed, and the application of high-temperature piezoelectric materials and lead-free piezoelectric materials is summarized. Finally, the future development direction of piezoelectric sensors is prospected.

The wire and arc additive manufacturing (WAAM) has gained more and more attention because of its unique advantages in forming large-scale components, and has become one of the most widely used metal additive manufacturing technology. The development history of WAAM is described. The influence of process parameters on the morphology of deposited layer and the evolution mechanism of microstructure is analyzed from the perspective of “shape and property control”. The numerical simulation methods for residual stress and their advantages and disadvantages are discussed, and it is pointed out that the combination of computational fluid dynamics and finite element method is one future research trend. The common methods for controling the residual stress and deformation, as well as the problems and challenges in wire and arc additive manufacturing, are summarized.

Plasma sprayed coatings have been widely used in surface protection engineering due to the excellent properties such as wear resistance, high temperature resistance and corrosion resistance. Pores are an important structural defect of plasma sprayed coatings. Excessive pores can lead to premature detachment failure of the coatings and shorten the service life, and therefore porosity is an important indicator to evaluate the coating quality. The pore formation mechanism, influencing factors, and the effect of the pores on the coating performance are briefly discribed. The research status of the porosity reduction of plasma sprayed coatings is reviewed from the aspects such as spraying process parameter optimization, laser remelting treatment, and modification of spraying materials. Moreover, the problems and development directions in the development of plasma sprayed coatings are summarized.

3D braided composites have a spatial network structure formed by continuous fiber bundles inside; therefore 3D braided composites have higher interlayer strength than traditional laminated composites, and have higher impact resistance and crack propagation resistance than metal materials. The meso-scale geometrical modeling methods of 3D braided composites are described in detail. The research progress on dynamic tensile and compression properties, dynamic failure criteria and high-speed impact properties of 3D braided composites is reviewed. The future research direction in meso-scale geometrical modeling and dynamic tensile testing of 3D braided composites is pointed out.

Silicon carbide ceramic has high strength and thermal conductivity, and good chemical stability, and is widely used in aerospace, petrochemical, integrated circuits and other fields; however, defects are easy to form in the silicon carbide ceramic during processing because of its high hardness and brittleness, which restricts the application of silicon carbide ceramic with complex structures. The preparation processes of silicon carbide ceramic with complex structures are described, and the advantages and disadvantages of the commonly used preparation technologies, such as cold isostatic pressing combined with pressure-free sintering, gel injection molding combined with reactive sintering, slip casting combined with reactive sintering, 3D printing combined with reactive sintering, are analyzed in order to provide a certain theoretical reference for the preparation of silicon carbide ceramic with complex structures.

Domain structure is deemed as the remarkable microstructural feature of ferroelectric materials, and its spontaneous polarization vector can be switched by the external applied electric/mechanical field (namely domain switching), leading to multiply electromechanical properties of ferroelectric materials. Starting from the theory of domain switching, research progress on the domain switching criterion is reviewed, and research results of the domain-wall dynamics and the domain switching-dependent fracture mechanics are described. It is aimed at providing some references for the micromechanics research of ferroelectric materials.

When the thermal stress caused by sudden temperature change of ceramic materials exceeds its strength, materials will happen to crack, peel and even fracture, and then failure. Therefore, the study of thermal shock resistance of ceramic materials becomes a hot spot. The evaluation theory of thermal shock resistance of ceramic materials and the methods for testing and characterizing are described. The methods of improving thermal shock resistance, including strengthening and toughening, improving thermal conductivity, reducing thermal expansion coefficient, and reducing elastic modulus, are reviewed. The external influencing factors of thermal shock resistance are summarized. The development direction of improving thermal shock resistance of ceramic materials in future is proposed.

Research progress on four piezoelectric application materials in the field of energy harvesting, including piezoelectric ceramics, multi-stacked piezoelectric ceramics, piezoelectric polymers and piezoelectric composites, is reviewed. The structural characteristics, preparation methods, and application occasions are highlighted, and the research trends of the piezoelectric materials in future is proposed.

In recent years, the rapid development of integrated circuit, heat exchanger, semiconductor industry has put forward higher requirements for the thermal conductivity of SiC ceramics. The thermal conductivity at room temperature of SiC ceramics is much lower than the theoretical value of single crystal SiC because of the defects such as lattice oxygen, grain boundary and porosity. The effects of additives and sintering process on the thermal conductivity at room temperature of SiC ceramics are reviewed. The future development direction of high thermal conductivity SiC ceramics is prospected.

Sputtering targets are the key raw materials for the preparation of thin films by magnetron sputtering, and their quality determines the performance of the sputtered thin films. Precious metal sputtering targets are widely used in the preparation of high-performance thin films because of their excellent physical and chemical properties. The research progress on the preparation methods, technical requirements and application of precious metal sputtering targets is reviewed. The development direction of high purity, large size, high utilization rate, and integrated development of target production and sputtering film is put forward.

On the basis of active and passive vibration control principles, four piezoelectric smart materials used in vibration control field, including single layer piezoelectric ceramics, multi-stacked piezoelectric ceramics, piezoelectric fiber composite and 0-3 type piezoelectric composite, are reviewed. The research progress of the structural characteristics, preparation process of the materails and their application for vibration attenuation in the fields of machinery manufacturing, aerospace and marine shipping are highlighted. The research direction in future of the piezoelectric materials is proposed.

Additive manufacturing is an important development direction of advanced manufacturing technique for metal parts, but the metal powder for additive manufacturing has some problems such as insufficient research and development, weak stability and incomplete standards, which seriously restrict its development. The basic principles of common spherical metal powder preparation techniques including centrifugal atomization method, two-stream atomization method and spheroidization method are summarized, and their advantages, disadvantages and development status are introduced. It is proposed that the development of domestic additive manufacturing powder preparation technique can start from two aspects. One is to carry out process and equipment improvement and standardization research on traditional methods, and build automated factories; the other is to strengthen the research on basic theories of powdering and explore new processes.

The shape memory effect, shape memory mechanism, types and preparation methods of thermal-induced shape memory polymer are reviewed. The influencing factors of shape memory performance are discussed. The application status of thermal-induced shape memory polymer is introduced. The application prospect of thermal induced shape memory polymer is expected.

As a commonly used metal material, copper is limited in its application due to its low strength. Because of its excellent comprehensive properties, graphene has attracted wide attention as a potential reinforcement. Graphene reinforced copper matrix composites combine the great properties of both copper and graphene, and have become an research hotspot. The preparation processes and comprehensive properties of graphene reinforced copper matrix composites are introduced. The characteristics of various preparation processes, strengthening mechanism and configuration design are emphatically discussed, and the improvement approaches to solve the two main technical difficulties of weak bonding of composite interface and difficult dispersion of graphene are summarized. Finally, the preparation process of graphene reinforced copper matrix composites is prospected.

Fatigue failure analysis processes and fatigue life assessment methods for metal materials are reviewed. The evaluation theories and models which were used widely in engineering, such as the Miner linear cumulative damage theory, the energy method, the elastic-plastic finite element method, the overload retardation model, are mainly introduced. The application conditions, advantages and disadvantages of these methods and models are also analyzed. With the development of the experimental technique and computer simulation technology, the assumptions will be more accuracy. Therefore the combined method of experiment and computer simulation for the fatigue life prediction and assessment of metal materials will be one of the most important development directions in the future.

As a main raw material for metal additive manufacturing, spherical metal powder characteristics play an important role in the performance of additive manufacturing parts. The efficient preparation of high-quality spherical metal powder has become an important development direction to promote the upgrading of additive manufacturing technologies and industrial applications. The main preparation methods of spherical metal powder including gas atomization, plasma rotating electrode atomization and plasma atomization are introduced. The technical principle and the influence of important process parameters on powder characteristics are discussed, and the future development direction of these three types of technologies is prospected.

Surface texture technique is a new type surface modification technique, which can effectively improve the tribological properties of materials through machining patterns with a certain shape and size, and with regular arrangement on the surface of materials by micro-fabrication technique. Surface texture plays an important role in mechanical friction pairs because of its outstanding advantages in improving the tribological characteristics of materials. The common texture preparation methods are introduced; the wear reducation mechanism of surface texture under different working conditions is described; the influence of surface texture topography and its geometric parameters on the wear resistance is summarized. The development direction of surface texture technology is prospected.

The rapid development of high technology puts forward higher requirements for the development of high-performance copper materials. Copper matrix composites have been widely used because of their high strength and good electrical and thermal conductivity, wear resistance, corrosion resistance and high-temperature stability; their preparation processes are constantly developing, and great progress has been made in recent years. The characteristics and research progress of the main preparation processes of copper matrix composites, including powder metallurgy technique, casting process, mechanical alloying, internal oxidation, in-situ synthesis, melt infiltration, and friction stir processing, are reviewed. The development direction of copper matrix composite preparation technology in the future is prospected.

Laser cladding technology is a new type of surface modification technology with broad development prospects, which not only meets the requirements for surface specific properties of materials, but also saves a lot of precious elements. The crack problem is one of the main obstacles restricting the wide industrial application and further development of laser cladding technology. The causes of crack formation in laser clading layers are described, and the crack control measures are reviewed, including the material composition design of cladding layers, setting the transition layer, process parameter optimization, matrix preheating, external field (force) assistance, etc. Finally the problems existing in the current crack control measures of laser cladding layers are summarized, and the future research direction is prospected.

When pulse currents are applied to metal materials, thermal and non-thermal effects will occur.The coupling of the two effects can promote dislocation movement and atom diffusion and increase the mobility of vacancy diffusion, leading to the evolution of microstructure of metal materials and forming an electroplastic effect.On the basis of the basic theory of electroplastic effects, the research progress on the pulse current treatment regulating the microstructure of metal materials and the application of pulse currents in auxiliary plastic processing and cutting processing are reviewed.It is pointed out that future researches are focused on the coupling mechanism of thermal effects and non-thermal effects in pulse current treatment and pulse current assisted processing, and current density distribution in application to complex structure parts, etc.

Development of high speed and high performance of mechanical equipments requires higher strength and better wear resistance of wear-resistant copper alloys. Although performance of traditional aluminum bronze series, manganese brass series and lead brass series alloys has been improved, their application scope is limited by various factors, such as material characteristics, processing technology and environmental protection, respectively. The application status and research progress of five typical wear-resistant copper alloys with high application values including Cu-Ni-Sn series, Cu-Al₂O₃ series, Cu-Nb series, Cu-C series (including copper/graphite, copper/graphene and copper/carbon nanotubes) and complex brass are described from preparation process, properties and application field. The problems in their development and application are analyzed, and their development prospect is also discussed.

Synchrotron radiation source with high spatial and temporal resolution is a large-scale scientific instrument representing kernel creativity of modern fundamental sciences. Research progress on in-situ loading machines based on high-energy X-ray 3D tomography is described. A set of in-situ loading rigs independently developed by the author team on the basis of Shanghai synchrotron radiation source and Beijing synchrotron radiation facility since 2011, including in-situ tensile, compression, low-cycle fatigue, high-cycle fatigue and super high-cycle fatigue testing machine as well as the sample environment, and researches on high-strength lightweight materials (such as laser welded aluminum alloy and additively manufactured aluminum and titanium alloys) are concisely discussed. The results show that in-situ loading machines play a key role in characterizing microstructural damage evolution of advanced materials, and also are the major supporting of large-scale scientific instruments related to national competitiveness.

G20Mn5 cast steel plates with thickness of 8 mm were connected by metal active gas (MAG) arc butt welding with one-side two-pass welding method. The microstructure, hardness, tensile property and fatigue property of the joint were studied. The results show that the joint had the good surface and no obvious welding defects were found. The joint consisted of base metal, heat affected zone and weld zone, and the heat affected zone was subdivided into incomplete normalized zone, normalized zone and overheated zone. From the base metal to the weld center, the hardness of the joint increased first and then decreased. The fusion zone had the highest hardness of about 70 HRB, and the hardness of the weld was 55-60 HRB, which was a little higher than that of the base metal. The tensile strength of the joint was obviously higher than that of the base metal, while the percentage elongation after fracture was lower than that of the base metal. The high cycle fatigue strength of the joint was equivalent to that of the base metal, and both fractured at heat affected zone. The properties of the joint met the design requirements.

Electrodeposition is the most widely used method for preparing nickel-based composite coatings at present. The characteristics of different electrodeposition methods are introduced. The effects of current density, bath pH, surfactant, content and size of second phase particles on the quality of nickel-based composite coatings are reviewed. The types and application status of nickel-based composite coatings are summarized. In the end, the future development of electrodeposited nickel-based composite coatings is prospected.

Under the background of increasing demand for lightweight, liquid die forging technique with excellent formability has been widely concerned. The lightweight design criteria and key points of lightweight design of equipments are summarized, and the application of liquid die forging aluminum alloy in equipments is introduced. The research progress on liquid die forging technique of aluminum alloy from the aspects of process principle and characteristics, forming materials, forming die and forming equipment is reviewed. Finally, the research and development direction of this technique in the future is put forward.

Fracture toughness is an important fracture resistance index of materials. The research status of plane strain fracture toughness, elastoplastic fracture toughness, crack tip opening displacement and dynamic fracture toughness testing techniques and their application to ductile cast iron materials are summarized. The influence of the temperature, microstructure and sample size on the fracture toughness of ductile cast iron is described. The problem of crack length testing in the fracture toughness specimen of ductile cast iron is discussed. The test method of fracture toughness of ductile cast iron based on J-Q (J integral-triaxial stress factor) theory is also described. It is believed that the multi-parameter fracture toughness testing based on the J-Q theory is the focus of future research. Furthermore, if the fracture toughness is to be used for engineering safety assessment, the loading mode and environment in actual service must be comprehensively considered during the testing.

With the further development of abundant marine resources, the friction and wear problems of marine mechanical equipment motion pairs have been paid more and more attention by researchers. The research status of main materials of motion pairs, including metal, ceramic and polymer in marine environment is summarized, the influencing factors of tribological properties of motion pair materials under marine conditions are analyzed, and the research progress of deep-sea tribology testing equipment is discussed, which can provide support for the selection and application of motion pairs of marine mechanical equipment.

The microstructure and tensile properties of 22MnB5 steel before and after hot stamping at 890 ℃ were studied and compared. The micromorphology evolution during uniaxial tensile of the test steel after hot stamping was investigated by in-situ tensile tests. The results show that the microstructure of the test steel before hot stamping was composed of ferrite and pearlite. After hot stamping, the microstructure changed to martensite, and the strength and the volume of strength and plasticity of the steel increased, while the plasticity decreased. During tensile, the test steel first underwent necking, then the original austenite grain boundaries were destroyed, leading to the initiation of microcracks, and the hole-type cracks were formed by debonding of inclusions. As the tensile continued, the cracks propagated and connected to each other, resulting in the fracture of the steel. A large number of dimples were observed on the tensile fracture surface of the hot stamped test steel, and the fracture form was microvoid coalescence fracture.

A three matching layer structure broadband medical phased array transducer was developed with 2-2 piezoelectric ceramic composite by three matching layer design scheme and KLM model optimization method. According to the design parameters, the medical phased array transducer was actually manufactured. The results show that the center frequency of actually produced medical phased array transducer was 2.95 MHz, and the relative bandwidth at -6 dB was about 83.2%, which were basically consistent with the theoretical design results (3.05 MHz, 87.8%) and met the design requirements. The transducer is expected to be used for imaging diagnosis of heart diseases.

Laminated structures designed by bionics principle can better solve intrinsic brittleness problems of carbide ceramics. It is now one of the most effective ways to strengthen and toughen carbide ceramics, and has good application prospects. The structural design features of laminar ceramics are described. The preparation, performance and main toughening mechanisms of SiC and B₄C laminar ceramics are reviewed. The development of carbide laminar ceramic materials is summarized and prospected.

The dynamic tensile properties of 6061 aluminum alloy was studied by the uniaxial tensile experiment at strain rates of 0.08,35,110,210,550 s^-1. The trure stress-ture strain curves were obtained at different strain rates. A plastic deformation constitutive model of the aluminum alloy was established based on the Johnson-Cook model, and the model was verified. The results show that, with the increase of strain rate, yield strength of 6061 aluminum alloy increased and elongation after fracuture decreased, but its fracture strength had not obvious changes. The constitutive model can describe well the change of flow stress of 6061 aluminum alloy during plastic deformation.

TC4 titanium alloy samples were formed by selective laser melting, and the influence of laser power (50-300 W) and laser scanning speed (250-1 750 mm·s^-1) on the microstructure and properties of the samples was studied. The results show that with the decrease of the scanning speed or the increase of the laser power, the forming quality of the samples was improved, the surface roughness was reduced, and the hardness on longitudinal section increased. The needle-like α' phase and nano-β phase were found in the microstructure of the samples. The size of the α' phase was relatively small, and the content of the β phase was relatively low at the relatively high scanning speed. Changing the scanning speed or the laser power had little effect on the tensile strength of the samples, but the elongation after fracture was relatively high at relatively low laser power or relatively high scanning speeds. When the laser power was 200 W and the scanning speed was 1 150 mm·s^-1, the samples had relatively good strength and plasticity matching.

Ferroelectric materials have unique photovoltaic properties due to their polarized electric field, and are widely used in many fields, especially in photovoltaic power generation. The generation mechanism of internal electric field (photovoltaic mechanism) in ferroelectric materials, and the effects of electric field regulation mechanism on photovoltaic properties of ferroelectric materials are reviewed from aspects of the preparation of narrow band gap ferroelectric materials, enhancing visible light absorption by self-doping of oxygen deficiency constructing composite heterojunction, preparing multipole axial molecular ferroelectrics, and regulating the domain orientation and distribution in ferroelectric materials by external polarization field. The research direction of improving photovoltaic performance by regulating internal electric field is pointed out.

Development in recent years of hot stamping steels, including ordinary hot stamping steel, hot stamping steel with high hardenability and oxidation resistance, high strength ductile hot stamping steel, ultra high strength hot stamping steel, high hydrogen embrittlement sensitivity hot stamping steel and ultra high strength hot stamping steel reinforced by nanoparticles, is summarized. The relation between lightweight and functionality of hot stamping steel parts, the relation between strength and hydrogen embrittlement and the influence mechanism of microstructure refinement on strength and toughness are analyzed. The suggestions for the further development direction of hot stamping steels are put forward.

Cermet is widely used in manufacturing cutting tools because of its excellent strength, high temperature thermal conductivity and thermal stability of metal materials, and high temperature resistance and corrosion resistance of ceramic materials. The lack of wear resistance and hardness of cermet limits its application range, which can be solved by preparing hard coating on its surface, but the bonding strength of the coating is weak, resulting in peeling off of the coating. The preparation method of the hard coating, the influencing factors on the bonding strength between the coating and the substrate are introduced, and the methods to improve the bonding strength of the hard coating are expounded. Finally, the preparation technique and the improvement of bonding strength of hard coating on cermet surface are prospected.

Based on three-dimensional Hashin failure criterion, and quadratic nominal stress criterion and BK failure criterion of the bilinear Cohesive damage model, the delamination damage of carbon fiber reinforced plastic unidirectional plate during drilling was simulated by VUMAT subroutine in ABAQUS/Explicit module, and the simulation results were verified by the ultrasonic C scan results after drilling. The effect of diameter and vertex angle of twist drill on delamination damage was studied. The results show that the tested maximum damage diameter of damage area of unitirectional plate after drilling was 25.6 mm, and the delamination factor was 2.56; the maximum damage diameter was 25 mm, and the delamination factor was 2.50 by finite element simulation. The relative error between experimental results and simulation results was only 2.4%, proving the accuracy of the finite element model. Compared with the top surface layer interface and intermediate interface, the delamination factor of the lower surface layer interface of unidirectional plate was the largest, and the delamination damage was the severest. The delamination factor increased with the increase of diameter and vertex angle of twist drill, and the delamination damage degree also increased.

The thermal oxygen accelerated aging test for different times (0,168,312,408 h) of polyethylene specimen was carried out at 85℃, and the maximum load of polyethylene specimen with different aging times was obtained by indentation testing technology. The linear relationship between yield strength and maximum load was established by finite element numerical simulation, and the yield strength after aging was calculated and compared with the tensile test results. The results show that with the extension of aging time, the yield strength of polyethylene specimens obtained by tensile test gradually increased, and the maximum load obtained by indentation test also gradually increased. The linear correlation coefficient between the maximum load and yield strength of polyethylene specimen indentation test established by finite element method was 0.995, and the relative error between the yield strength of polyethylene specimen with different aging times calculated with the maximum load obtained by indentation test and the tensile test results was less than 1.5%, indicating that the indentation testing technology could accurately obtain the yield strength of polyethylene after aging.

45 steel rods in forged and normalized state with a diameter of 8 mm for sealing plug were quenched at 750-880℃ for 15 min and high temperature tempered at 550℃ for 30 min. The microstructure, fracture morphology and hardness of the specimens at different quenching temperatures were studied. The effect of quenching temperature on quenching cracking was analyzed and the heat treatment process was optimized. The results show that the specimens did not crack after quenching at 750℃ and 780℃, and cracked after quenching at 800-880℃. With increasing quenching temperature, the ferrite content in microstructure decreased, the grain size increased, and the hardness first increased and then decreased. When the quenching temperature ranged from 800℃ to 830℃, the cause of quenching cracking was that the cooling rate of undercooled austenite in the martensite transformation phase region was too large, and the structural stress was concentrated in the outer layer of the specimen, which led to the propagation of crack in a mixed mode of intergranular and transgranular. When the quenching temperature ranged from 850℃ to 880℃, the grain boundary was weakened due to the higher quenching temperature, and cracks propagated along grain boundaries under the combined action of the structural stress and the thermal stress. The best tempered sorbite structure and relatively high hardness of 45 steel could be obtained and the quenching cracking could be avoided by setting a slow cooling process of 3-5 s at room temperature before quenching at 830℃ and then tempering.

Through the optimization design of material formula, friction blocks of copper-based powder metallurgy brake pad for high-speed train was prepared by the powder metallurgy method, and the physical and mechanical properties were tested. Then a new type of floating brake pad was assembled through the optimization of the pad structure, and the friction and wear properties of the pad were measured. The results show that shear strength of friction blocks for the brake pad was above 7 MPa. The average friction coefficients of the brake pad was 0.37±0.05 and the average wear loss was 0.126×10^-6 cm³ ·J^-1,which met the requirements of the friction and wear properties for brake pad specified by International Railway Union. The braking properties of the tested brake pad also met the requirements of the 350 km ·h^-1 and above high-speed trains.