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4D printing of continuous fiber‐reinforced shape memory polymer (SMP) composites is a promising technology that has emerged in recent years. Nonetheless, combining superior load‐bearing capacity with fast‐response shape reconstruction in intelligently‐driven structures is still a challenge due to the inferior thermal conductivity and mechanical properties of the composites along the transverse and thickness directions of the continuous fibers. In this study, a multi‐scale 4D printing strategy for 3D carbon medium‐reinforced thermosetting SMP (Ts‐SMP) is proposed. This 3D reinforcement structure is realized by graphene synergized with continuous carbon fibers (GR‐CCF) to provide multidirectional thermal conductivity and load‐bearing paths for the composites. The reinforcement mechanism of GR‐CCF for Ts‐SMP is systematically investigated. The GR‐CCF reinforced Ts‐SMP composites exhibited superior performance, with a bending strength of 676.99 MPa, shape fixation ratio, and shape recovery ratio of 98.62% and 99.07%, respectively, and the local shape response reconfiguration within 6 s under near‐infrared light excitation. This study provides a reference for the integrated fabrication of high‐performance Ts‐SMP composites for complex structures. The composites offer prospective applications in space deployable antenna locking hoops, flexible solar sail support ribs, and optically driven robot actuators. [ABSTRACT FROM AUTHOR]

To overcome the dependence of continuous carbon fiber reinforced thermoset composites (CCFRTCs) on molds during the curing, a thermoset continuous fiber prepreg filament and thermoplastic filament alternate printing method was proposed. CCFRTCs with thin thermoplastic shells were prepared based on the method, and the confinement of thermoplastic shells enabled the mold‐less curing of CCFRTCs. The influence of key curing process parameters on the flexural properties of the specimens was systematically investigated. The experimental results showed that the flexural properties of the prepared composites were correlated positively with the vacuum degree and showed a tendency of first increasing and then decreasing with the increasement of impregnation time and curing temperature. Through x‐ray computed tomography (CT) and scanning electron microscope (SEM) analysis, the effect of key curing process parameters on the flexural properties of the CCFRTCs was clarified. Under the guidance of suitable curing process parameters, the flexural strength and modulus of the composite reached 482.89 MPa and 35.11 GPa, which were significantly better than most existing 3D printed continuous carbon fiber reinforced polymer composites. Finally, complex components were prepared to verify the feasibility and versatility of the technique. Highlights: A CCFRTCs mold‐less curing method was proposed.The effect of key parameters on the properties of CCFRTCs was clarified.Both the advantages of thermoset and thermoplastic materials were obtained.Complex components with low porosity were prepared. [ABSTRACT FROM AUTHOR]

There are various shaped sections of slotted-in steel plates and timber grooves among the bolted timber joints with slotted-in steel plates to satisfy the design and assembly criteria in practical engineering. The different shapes affect the performance but have not been widely researched. To visualize the effect of shaped sections on the joints and provide some experience for targeting improving the ductility, we performed monotonic loading tests parallel to the grain on 16 sets of the proposed end U-shaped carbon fiber reinforced plastics (CFRP)–bolted timber joints with slotted-in corrugated steel plates. The effects of the wavelength, wave height, wave angle, timber thickness, number of CFRP layers, and interaction between the parameters were mainly considered. The results showed that the joints were susceptible to failure as a result of a number of manifestations, including shear damage, pressure damage, opening-mode cleavage in the grain direction (TL cleavage), CFRP cleavage, etc. Similarly, the joints had multiple combinations of yielding deformation modes of bolts, which included IS , IS & IIIS , IIIS , IIIS & IV, and V. The load-displacement curve showed that the joints mainly undergo the elastic stage, the fracture failure transition stage, and the fracture failure stage without an obvious yield stage. According to the experimental results, an orthogonal parametric analysis of the mechanical properties was conducted and the degree and pattern of each parameter were obtained. Among them, each parameter affected the elastic stiffness relatively less; wave height and wave angle had relatively significant influences on the ultimate strength and ductility, and the ultimate strength fluctuated with the increasing wave height, but negatively correlated with wave angle, while the ductility was negatively correlated with both. Additionally, a strength formula was derived by theoretical analysis, and a good agreement was indicated by the average ratio of 1.03 between the theoretical and experimental results. This study contributes to the understanding of the effect of shaped slotted-in steel plates on the mechanical behavior of bolted timber joints with slotted-in steel plates and provides some theoretical and experience basis for the reinforcement. However, this study is mainly focused on spruce and slotted-in corrugated steel plates, which still need to be adequately investigated for other tree species and cross-sectional forms, especially the fracture characteristics. In addition, the group effect of bolted timber joints is more significant, which needs to be specifically studied for the design in engineering applications. [ABSTRACT FROM AUTHOR]

Elastocaloric cooling has no environmental effects during operation, and achieving a compact structure especially the driver is significant for its commercialization. In this article, a compact, standalone crankshaft driven single long NiTi tube compressive elastocaloric cooler is developed. A crankshaft driver was designed and fabricated to drive a compressive elastocaloric regenerator utilizing a single long polycrystalline superelastic NiTi shape memory alloy tube (outer diameter 5 mm, wall thickness 1 mm, and initial length 305 mm). A novel design of ceramic heat insulation plate was applied to the cooler to reduce the conduction heat loss from the NiTi tube to the stainless-steel loading heads. The cooling performance of the cooler was characterized using synchronized thermocouples and infrared thermography, and the specific cooling(heating) power, temperature span, and coefficient of performance of up to 65(125) W·kg−1, 9.1 K, and 5.0, respectively were measured. The progressions of the temperature span, specific cooling(heating) power, and coefficient of performance with the operation cycle and temperature lift were analyzed. An energy analysis revealed that the heat transfer fluid carried out only 14% of the latent heat generated by the NiTi tube, which demonstrated a potential to enhance the cooling performance by the improvement in the regenerator structure. [ABSTRACT FROM AUTHOR]

This paper is devoted to suppressing the lumped disturbance, which is mainly composed of static and dynamic unbalanced disturbance, to ensure the imaging quality of the rotating payload satellite system with a five-degree-of-freedom active magnetic bearing. The dynamic model of lumped disturbance in imaging phase is established to design the balancing error index of payload unbalance, and the effect of bearing mechanical characteristics is analyzed. A novel fixed-time extended state observer is proposed to estimate unknown lumped disturbance and uncertainty. On this basis, a novel quaternion-based fixed-time nonsingular terminal sliding mode controller is presented to achieve high precision, high stability, and chattering-free attitude control. The complete proof on the faster convergence performance of the presented sliding mode surface compared to the existing sliding mode surfaces and the fixed-time convergence of the presented controller is provided. Numerical simulation results are carried out to verify the lumped disturbance modeling accuracy and the effectiveness of the proposed controller. [ABSTRACT FROM AUTHOR]

Graphene is often used to improve interlaminar fracture toughness of carbon fiber/epoxy resin (CF/EP) composites. It is still a challenge to improve the toughness while maintaining the in-layer properties. In this study, 2D graphene oxide carbon fiber reinforced epoxy resin matrix (2D CF-GO/EP) composites were prepared by a vacuum infiltration hot-press forming experimental system (VIHPS), and three-point flexural and end notch flexural (ENF) tests were carried out. With the increase of the fiber mass fraction in the composites, the mode II interlaminar fracture toughness (GIIC) layers decrease gradually, and the bond property between the fiber and matrix interface layer becomes worse, because the accumulation of dense fiber bundles reduces the matrix penetration ability of cracks. However, the flexural properties increased first and then decreased, and reached the best flexural properties at 64.9%. When the fiber mass fraction is too high, the interlamellar bonding properties will decrease, and the fiber bundles will compress and affect each other. The delamination phenomenon will occur between the layers of the composites, which affects the overall bearing strength and stress limit of the composites. The results of the study show that the composites prepared by VIHPS have excellent mechanical properties, and the content of carbon fiber plays an important role in the influencing factors of the interlaminar and in-layer properties of composites. [ABSTRACT FROM AUTHOR]

In this article, the influence of graphene oxide (GO) content on the morphology and properties of carbon fiber/epoxy (CF/EP) composites was investigated. To obtain CF/EP composites with uniform dispersion of GO, electromagnetic stirring and ultrasonic dispersion techniques were employed in the wet transfer process. Combined with a new molding process, CF/EP composites with different GO content were prepared. The test results showed that the bending strength of CF/EP composites could be effectively improved by adding GO, among which 0.5 wt% GO–CF/EP composite exhibited the best bending strength and modulus increased by 47.20% and 21.24%, up to 1158.9 MPa and 115.3 GPa. Likewise, the mode I interlaminar fracture toughness (GIC) of the composite at the beginning of crack and the maximum during the propagation increased by 28.13% and 21.57%, reached 327.5 and 656.6 J/m2, respectively. The distribution of GO in the composites and the fracture morphology of the composites were observed. Finally, according to the test results and microscopic morphology analysis, the enhancement and failure mechanism of GO in CF/EP composites were clarified. It was found that GO could improve the properties of CF/EP composites by enhancing the interface properties of CF/matrix, enhancing the strength of the matrix and forming a net‐like structure inside the matrix. [ABSTRACT FROM AUTHOR]

Five group of different layering methods of basalt/carbon fiber (BF/CF) hybrid reinforced resin matrix composites are prepared by vacuum infiltration hot-press forming process. The bending properties with different layering methods have obvious distinguishing, B5C1 (B-Basalt fiber, C-Carbon fiber) has the lowest bending strength of 283 MPa, and B1C5 has the highest bending strength of 404 MPa. The observation of microstructure shows that infiltration effect of composites is good, and matrix is fully and evenly distributed in fibers. The bending fracture morphology is also relatively ideal. Some of the fibers show brittle fracture morphology and others show pull-out morphology, further indicating that the fibers are tightly bound to the matrix. In addition, the ultimate bending strength of composite single-layer plate is calculated, and the formula for calculating the bending strength of the composite laminate is established based on the laminate principle. By modifying the calculation formula, more accurate results are obtained. The experimental results are in good agreement with the theoretical ones, and the reliability of the calculation method is verified. The results showed that carbon fiber enhanced the bending strength of hybrid laminates, but with the increase of carbon fiber content, the strengthening effect decreased [ABSTRACT FROM AUTHOR]

Three‐dimensional carbon fiber reinforced resin matrix composite can effectively overcome the defects of traditional composite in the interlayer strength and stiffness, and has been widely used. Herein, the threshold infiltration pressure of resin in three‐dimensional carbon fiber preform is respectively calculated as 0.170 and 0.973 MPa from the perspective of statics and dynamics. The static calculation ignores the additional pressure caused by the viscous resistance of the resin during the infiltration process, which deviated greatly from the actual value. Therefore, the dynamics calculation value is used as a reference to extrusion pressure in the experiment. The composites with extrusion pressure of 1, 2, 3, 4, and 5 MPa are prepared by vacuum infiltration hot pressing process. Through the study of the infiltration microstructure and bending fracture morphology of the composite, it is found that when the extrusion pressure is 3 MPa, the preparation effect is the best. At this time, the bending strength of the composite is 540 MPa, which is 92.86% and 71.43% higher than that at 1 and 5 MPa, respectively. It is indicated that the extrusion pressure is a key parameter in the composite preparation process and needs to be selected reasonably. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced shape memory polymer composite (SMPC) is a kind of smart material with shape memory characteristics, which is widely used in aerospace, biomedicine, robotics and other fields. In this paper, SMPC was prepared by heating molding process at five different molding temperatures. The effect of molding temperature on the shape memory performance of SMPC was studied. The results show that the shape memory properties of SMPC are closely related to the infiltration effect during the preparation process. When the molding temperature is 70 °C, SMPC has an optimum penetration effect and the preparation defects are effectively controlled. The shape fixing rate is 84.3%, and the shape recovery rate is 94.7%, which lays a foundation for the better application of shape memory composite. [ABSTRACT FROM AUTHOR]

Micro liquid dispensing technology is widely used in the field of electronic packaging. This study presents a lumped parameter model of a needle-type piezostack-driven jetting dispenser, which can produce small high viscosity adhesive droplets with a high driving frequency. After describing the structural components and operating principles of the dispenser, a lumped parameter model for the system is derived by integrating the sub-models of the structural and fluid parts. According to the lumped parameter method, the fluid channels of the dispenser have been divided into several lumps to obtain a more accurate performance. Based on the proposed model, the jetting dispenser is designed and manufactured, and its performance is then evaluated through both computer simulations and experiments. Further experimental studies about its working properties based on the proposed dispenser are carried out. The results are used to guide the design and control works about the proposed dispenser. [ABSTRACT FROM PUBLISHER]

Abstract: With the wide application of multi-core processor, the software is required to be more efficient. Although Massey Algorithm solved the comprehensive problems of the linear feedback shift register, its research mainly focused on the single core platform. Based on the multi-core processor platform, parallel algorithm was designed and realized, the distribution problem of multi-core processor in Massey Algorithm was solved. After the analysis and verification of Massey iteration algorithm, the improved algorithm made the running time shorter, and the efficiency of the software enhanced dramatically. [Copyright &y& Elsevier]

In order to prepare a carbon-fiber-reinforced polymer composite (CFRP) with ideal microstructure and properties, a new vacuum pressure infiltration CFRP method is proposed based on an analysis of existing CFRP preparation process methods. Research on composite material preparation systems was carried out by using this new method principle. The system mainly includes a fiber pre-forming module, a vacuum heating infiltration module, a hot-press curing molding module, and a data acquisition control module. Under the conditions of natural curing at 0 MPa + 6 h + 25 °C, vacuum heating curing at –0.05 MPa + 30 min + 80 °C, and hot-press curing at 0.7 MPa + 5 min + 50 °C, a two-dimensional (2D) CFRP with excellent microstructure and properties was successfully prepared. Observing the microstructure of the prepared composite material, it can be found that the inside of the composite material was sufficiently and uniformly infiltrated, and common preparation defects such as holes and delamination were effectively controlled. Through the performance test, the bending strength of the material reached 790 MPa. [ABSTRACT FROM AUTHOR]

The current miniaturization trend of microelectronic devices drives the size of solder joints to continually scale down. The miniaturized joints considerably increase intermetallic compounds (IMCs) volume fraction to trigger mechanical reliability issues. This study investigated precise relationships between varying IMC volumes and mechanical properties of Ni/Sn(20μm)/Ni micro-joints. A designed method that followed the IMC volume as the only variable was used to prepare micro-joint samples with different IMC volumes. The continuously thickened Ni3Sn4 IMCs exhibited a noticeable morphology evolution from rod-like to chunky shape. The subsequent tensile tests showed unexpected tensile strength responses as increasing Ni3Sn4 volume, which was strongly associated with the Ni3Sn4 morphological evolutions. Fractographic analysis displayed that the ductile fracture dominates the 20%–40% IMC micro-joints, whereas the brittle fracture governs the 40%–80% IMC micro-joints. For the ductile fracture-dominated joints, an abnormal reduction in strength occurred as increasing IMCs volume from 20% to 40%. This is primarily due to severe stress concentrations caused by the transformed long rod-typed morphology of the Ni3Sn4. For the brittle fracture-dominated joints, the strength appeared a monotonous increase as the Ni3Sn4 volume increased. This may be attributed to the increased crack resistance resulting from continuous coarsening of the chunky Ni3Sn4 without any voids. Moreover, the finite element analysis was provided to further understand the joint failure mechanisms. [ABSTRACT FROM AUTHOR]

The critical infiltration pressures of the matrix in a two-dimensional (2D) carbon fiber preform were calculated theoretically, and the calculated values of the static and dynamic models were 0.115 and 0.478 MPa, respectively. Compared with the dynamic model, there is no viscous resistance or infiltration front gas pressure in the static model, so the static value is obviously lower than the dynamic value. To verify the rationality of theoretical calculation, 2D carbon fiber reinforced plastics (2D-CFRP) with infiltration pressures of 0.5, 0.6, 0.7, 0.8, and 0.9 MPa were prepared by the vacuum infiltration hot pressing molding process. The microstructure of the composite was observed and the bending strength was tested by three-point bending test. The results show that the infiltration pressure has an important influence on the infiltration effect and the bending fracture morphology. When the infiltration pressure is 0.7 MPa, the composite has an excellent infiltration effect. The fibers distribute reasonable in the fracture. Stress can be effectively transferred when the composite material is loaded. And the bending strength of the composite material reaches 627 MPa at this time. [ABSTRACT FROM AUTHOR]

A dynamic deviation memory polynomial (DDMP) model for digital predistortion is proposed to compensate the non‐linear distortion of the power amplifier. It is based on the memory polynomial model and dynamic deviation reduction‐based Volterra (DDRV) model. Compared to the DDRV model, the proposed model shows better modelling accuracy under the same complexity. The effectiveness of the DDMP model has been verified by simulation and experiment results. [ABSTRACT FROM AUTHOR]

As micro solder-joints downsize to less than 10 μm in 3-dimensional (3D) TSV (Through Silicon Via) chip stacking, rapidly fabricating reliable micro-joints without collapse in chip stacking is regarded as a critical issue. A practicable method with a suitable temperature gradient (TG) and Ni/Sn(10 μm)/Ni interconnection structure was developed compared with conventional transient liquid phase (TLP) bonding. Using this method, the micro-joint fully composed of Ni 3 Sn 4 intermetallic was fabricated within 17 min bonding time. It is nearly three times faster than that under conventional TLP bonding, which may overcome this technology limitation caused by longer bonding times. This fast TG-TLP method provided an asymmetry growth characteristic with thicker Ni 3 Sn 4 at the cold end and thinner Ni 3 Sn 4 at the hot end. The basic micro-joint formation mechanisms were suggested and experimentally verified. Furthermore, the properties of the fabricated Ni 3 Sn 4 micro-joint were evaluated in this study. The results demonstrated its desirable features such as high melting temperature, stable single-phase constitution, stronger mechanical strength and low thermal resistance. Finally, the collapsed micro solder-joint issue was completely solved resulting in higher reliability. • Reliable Ni 3 Sn 4 micro-joint with high temperature and thermal stability was fabricated rapidly. • The rapid formation mechanism of such a joint was analyzed and experimentally verified. • This joint exhibited excellent mechanical and physical properties for 3D TSV packaging. • This joint can solve the collapsed solder-joint issue during TSV chips stacking. [ABSTRACT FROM AUTHOR]

Background: Because racial discrepancies in dental characteristics are known to exist, designing preadjusted appliances according to racial normal occlusion data would be expected to improve treatment results. However, whether modifications based on racial characteristics can improve treatment outcomes in the clinic remains to be investigated., Methods: To study the influence of prescription type on treatment outcomes, 91 patients treated with Chinese or Roth prescription appliances were selected as an initial sample. Two groups of patients were selected by propensity score matching (1:1) to limit the effects of confounding factors, including age, sex, case complexity, and extraction plan. Discrepancy Index and cervical vertebral maturation values were used to quantify case complexity and patient age, respectively. After matching, the final sample of 60 patients consisted of two groups of 30 patients each: group 1 had been treated with a Chinese prescription appliance and group 2 had been treated with a Roth prescription appliance. ABO casts and radiograph evaluation (CR-Eval) and lateral cephalograms were utilized to compare the treatment outcomes of the two groups., Results: The total ABO scores of groups 1 and 2 were 22.03 and 23.87, respectively. There were no significant differences between the two groups in total ABO score or in seven other sub-scores; however, there was a significant difference between the two groups in mandibular canine alignment score., Conclusions: There are no significant differences in overall treatment outcomes between the Chinese and Roth prescription appliances. The Chinese prescription yielded better alignment results in the mandibular canine for Chinese patients., Competing Interests: The authors declare there are no competing interests., (©2021 Chu et al.)