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The corrosion behavior of 3Cr steel in simulated oilfield CO2 and formation water environment at different temperature and partial pressure of CO2 were investigated using dynamic immersion tests, scanning electron microscopy inspection and X-ray diffraction analysis. The result demonstrated that with an increasing of temperature, the corrosion rate of 3Cr steel decreased, and reached the maximum corrosion rate when the partial pressure of CO2 was 0.5MPa. The high content of Ca2+ in the formation water had also played an important role in the corrosion behavior of the 3Cr steel for it can lead to a deposition of the CaCO3 on the surface of the specimen.

Stretchable strain sensor detects a wide range of strain variation and is therefore a key component in various applications. Unlike traditional ones made of elastomers doped with conductive components or fabricated with liquid conductors, ionically conductive hydrogel-based strain sensors remain conductive under large deformations and are biocompatible. However, dehydration is a challenging issue for the latter. Researchers have developed hydrogel-elastomer-based strain sensors where an elastomer matrix encapsulates a hydrogel circuit to prevent its dehydration. However, the reported multi-step approaches are generally time-consuming. Our group recently reported a multimaterial 3D printing approach that enables fast fabrication of such sensors, yet requires a self-built digital-light-processing-based multimaterial 3D printer. Here, we report a simple projection lithography method to fabricate hydrogel-elastomer-based stretchable strain sensors within 5 minutes. This method only requires a UV projector/lamp with photomasks; the chemicals are commercially available; the protocols for preparing the polymer precursors are friendly to users without chemistry background. Moreover, the manufacturing flexibility allows users to readily pattern the sensor circuit and attach the sensor to a 3D printed soft pneumatic actuator to enable strain sensing on the latter. The proposed approach paves a simple and versatile way to fabricate hydrogel-elastomer-based stretchable strain sensors and flexible electronic devices.

Shape reconfiguration is ubiquitous in nature and widely used in many applications such as soft robotics, metamaterials, energy absorption and tissue engineering. Shape reconfigurable soft actuators, due to their ability to adapt and adjust in complex and unpredictable working environment, have been designed by the use of various delicate structures and active materials. However, soft actuators that exhibit reconfigurable helical deformation have not been proposed; they have the advantage of integrating both bending and twisting actuations in one deformation mode. In this work, we present a thermal-induced shape reconfigurable soft actuator that shows reversible actuations with vastly shape differences under thermal stimulus. It exhibits helical deformation at lower temperature and mainly in-plane bending at relatively higher temperature. The reversible shape transition is controlled by a thermal stimulus that changes the anisotropy of the structure, which consists of shape memory polymer fibers embedded in a homogeneous elastic matrix. A theoretical model is proposed based on the minimum potential energy that incorporates the thermomechanical behavior of the shape memory polymer fibers. Experiments are conducted and the results agree well with the theoretical modeling. Using the theoretical model, we establish design principles for reconfigurable soft actuators whose functional response is programmable given the architecture and external stimulus. A six-handed helical soft actuator, constructed to demonstrate its programmable deformation, is utilized to catch a living fish in water.

A novel bolt-connected precast concrete wall panel structural system has recently been proposed for low-rise buildings in rural areas. The system features replaceable distributed bolt-conne...

The recently developed dual-stage 3D printing reprocessable thermosets (3DPRTs) utilize acrylate functional groups to enable the ultra-violet based 3D printing (Stage I), and employ bond exchange reaction (BERs) to tailor the network structure for mechanical properties enhancement and impart the reshapeability, reparability, and recyclability into traditionally unprocessable thermosets (Stage II). 3DPRT provides a practical solution to address environmental challenges associated with the rapid increase in the consumption of 3D printing materials. However, due to the nascent state of development, fundamental understanding of the chemomechanics during the processing of 3DPRTs is still lacking. In this paper, we present detailed experimental and theoretical studies to understand the effect of thermal treatment condition at Stage II on the evolution of network structure and thermomechanical properties of 3DPRTs. A chemomechanics theory is defined to link the molecular-level BER kinetics to the macroscale thermomechanical properties of 3DPRTs during the thermal treatment. A thermo-viscoelastic multi-branched constitutive model is then established to capture the elastic and glass transition behaviors during the Stage II processing. The developed theory is able to capture the experimental observations on the mechanical properties enhancement and provide theoretical guidance for the network design and the selection of thermal treatment conditions to tailor the final mechanical properties of 3DPRTs.

Conventional 4D printing technologies are realized by combining 3D printing with soft active materials such as shape memory polymers (SMPs) and hydrogels. However, the intrinsic material property limitations make the SMP or hydrogel-based 4D printing unsuitable to fabricate the actuators that need to exhibit fast-response, reversible actuations. Instead, pneumatic actuations have been widely adopted by the soft robotics community to achieve fast-response, reversible actuations, and many efforts have been made to apply the pneumatic actuation to 3D printed structures to realize passive 4D printing with fast-response, reversible actuation. However, the 3D printing of soft actuators/robots heavily relies on the commercially available UV curable elastomers the break strains of which are not sufficient for certain applications which require larger elastic deformation. In this paper, we present two simple approaches to tune the mechanical properties such as stretchability, stiffness, and durability of the commercially available UV curable elastomers by adding: (i) mono-acrylate based linear chain builder; (ii) urethane diacrylate-based crosslinker. Material property characterizations have been performed to investigate the effects of adding the two additives on the stretchability, stiffness, mechanical repeatability as well as viscosity. Demonstrations of fully printed robotic finger, grippers, and highly deformable 3D lattice structure are also presented.

Shape-shifting structures have gained growing interest recently and found wide applications in areas such as soft robotics, biomedical devices and self-folding origami, attributed to their ability to construct complicated shapes directly from simple structures. However, an efficient method to design and fabricate programmable 3D shape-shifting structures from 2D polymer films still lacks. In this work, we design programmable shape-shifting 3D structures via the release of internal gradient stress using the frontal photopolymerization (FPP) method. First, the relation between the non-uniformly distributed material and loading parameters, and the geometric and fabrication parameters are established theoretically. The finite element (FE) model is then developed based on the theoretically obtained material and loading parameters. Next, the elastic instability in the shape-shifting behaviors of a cured film is captured through an elastic energy minimization. Furthermore, by using grayscale light patterns, it is shown that we can selectively manipulate the geometric and fabrication parameters to improve the design freedom of various complex 3D structures.

Spatial control of material properties is highly desirable in additive manufacturing of functional structures with complex geometries. Whereas most previous efforts focused on developing new printing or material systems, we propose a new voxel design strategy of constructing digital materials to provide the additively manufactured polymeric structures with spatially customized thermomechanical properties. In our approach, a matrix-inclusion composite layout is adopted in the linearly patterned voxels that perform as building blocks to construct bulk material. Through rational design of voxel size and inclusion content, the printed polymeric digital material displays a tunable storage modulus up to three orders of magnitude and glass transition temperature ranging from 0 °C to 60 °C. By taking advantage of the design freedom, we demonstrate a sequential folding structure with spatially tunable actuation speed, and multi-stable configurations that trap elastic energy in deterministic collapse sequences. Overall, our approach provides an effective and convenient way of spatially customizing material properties for additive manufacturing and offers instructive inspirations to the realm of digital fabrication.

Extraordinary optical, electrical and chemical properties of 2D materials have potential to be useful for quick and sensitive detection of pathological diseases. One important example is malaria disease that can progress rapidly and cause death within days. Therefore, fast, accurate and cost-effective malaria diagnosis available at the point of care is urgently needed to facilitate precise treatment. Here we report rapid and highly sensitive malaria detection with an inexpensive graphene-protected copper surface plasmon resonance biosensor. Using phase sensitive surface plasmon resonance technique and a graphene functionalization protocol for attaching end-tethered DNA probes that were complementary to a malaria specific DNA target, we were able to significantly improve the detection limit of the malarial plasmodium parasite. The phase sensitivity of our graphene-enhanced sensors exceeds by two orders of magnitude the sensitivity of analogous optical biosensors. This enhanced sensitivity could provide means to detect low copy number bacterial infectious agents and to associate dormant bacterial populations with chronic inflammatory diseases using simple label-free optical detection.

Digital Light Processing (DLP) 3D printing enables the creation of hierarchical complex structures with specific micro- and macroscopic architectures that are impossible to achieve through traditional manufacturing methods. Here, this hierarchy is extended to the mesoscopic length scale for optimized devices that dissipate mechanical energy. A photocurable, thus DLP-printable main-chain liquid crystal elastomer (LCE) resin is reported and used to print a variety of complex, high-resolution energy-dissipative devices. Using compressive mechanical testing, the stress-strain responses of 3D-printed LCE lattice structures are shown to have 12 times greater rate-dependence and up to 27 times greater strain-energy dissipation compared to those printed from a commercially available photocurable elastomer resin. The reported behaviors of these structures provide further insight into the much-overlooked energy-dissipation properties of LCEs and can inspire the development of high-energy-absorbing device applications.

Nature builds biological materials from limited ingredients, however, with unparalleled mechanical performances compared to artificial materials, by harnessing inherent structures across multi-length-scales. In contrast, synthetic material design overwhelmingly focuses on developing new compounds, and fails to reproduce the mechanical properties of natural counterparts, such as fatigue resistance. Here, a simple yet general strategy to engineer conventional hydrogels with a more than 100-fold increase in fatigue thresholds is reported. This strategy is proven to be universally applicable to various species of hydrogel materials, including polysaccharides (i.e., alginate, cellulose), proteins (i.e., gelatin), synthetic polymers (i.e., poly(vinyl alcohol)s), as well as corresponding polymer composites. These fatigue-resistant hydrogels exhibit a record-high fatigue threshold over most synthetic soft materials, making them low-cost, high-performance, and durable alternatives to soft materials used in those circumstances including robotics, artificial muscles, etc.

4D printing is an emerging fabrication technology that enables 3D printed structures to change configuration over "time" in response to an environmental stimulus. Compared with other soft active materials used for 4D printing, shape-memory polymers (SMPs) have higher stiffness, and are compatible with various 3D printing technologies. Among them, ultraviolet (UV)-curable SMPs are compatible with Digital Light Processing (DLP)-based 3D printing to fabricate SMP-based structures with complex geometry and high-resolution. However, UV-curable SMPs have limitations in terms of mechanical performance, which significantly constrains their application ranges. Here, a mechanically robust and UV-curable SMP system is reported, which is highly deformable, fatigue resistant, and compatible with DLP-based 3D printing, to fabricate high-resolution (up to 2 µm), highly complex 3D structures that exhibit large shape change (up to 1240%) upon heating. More importantly, the developed SMP system exhibits excellent fatigue resistance and can be repeatedly loaded more than 10 000 times. The development of the mechanically robust and UV-curable SMPs significantly improves the mechanical performance of the SMP-based 4D printing structures, which allows them to be applied to engineering applications such as aerospace, smart furniture, and soft robots.

Shape memory polymers (SMPs) are a class of active materials that have the capability of fixing a temporary shape and recovering to a permanent shape in response to environmental stimuli. While SMPs have been studied intensively, researchers paid comparatively fewer attentions to SMPs exhibiting anisotropic mechanical and shape memory behaviors by controlling the microscopic architectures. At the same time, the rapidly developed three-dimension (3D) printing technologies enable us to directly print complex 3D structures with multimaterials and provide possibilities to fabricate anisotropic shape memory polymer by precisely controlling the microstructure of fibers. In this paper, we present a new approach for fabricating printed anisotropic shape memory elastomeric composites (p-ASMECs) by taking advantage of 3D printing. In the fabrication process, an elastomer is first printed as matrix and the orientation of fibers is defined by the precisely printed channels. By interrupting the printing process, the printed channels are filled with the crystallizable polymeric fibers that endow the shape memory effect into the composite system. The p-ASMECs exhibit large, controllable anisotropy in both mechanical and shape memory behaviors that can be precisely controlled by geometric parameters of the microstructure such as fiber's volume fraction and position in space. To facilitate design of p-ASEMCs, we also developed a thermomechanical constitutive framework to describe the complex, anisotropic, larger deformation thermomechanical behaviors of p-ASEMCs. The developed constitutive model, used to explain the phenomenon that the lowest stiffness of p-ASEMCs occurs at the fiber orientation angle θ ≈ 55°, successfully predicts the anisotropic shape memory behavior of p-ASMECs, guides the design to enhance the temporary shape fixity, and simulates the shear deformation of the temporary shape after completely releasing the external constraints.

KDP (KH2PO4) crystal is a kind of excellent nonlinear optical crystals, which has been widely used in nonlinear optical and Inertial Confinement Fusion (ICF) engineering. KDP crystal with the characteristics of low hardness, high brittleness, easy deliquescence and temperature-sensitive is easy to crack during the crystal growth, taken out from crystallizer, and the process of slicing. Stress concentration caused by the initial internal stress redistribution and the growth defect in KDP crystal is an important reason of KDP crystal cracking during sawing process. The numerical simulation model of the KDP crystal containing spherical cavity defect and sawing with fixed abrasive wire saw is established by finite element method in this paper. The effects of initial internal stress, spherical cavity defect on sawing stress are investigated. The maximum tensile stress near the defect during the sawing process is simulated and analyzed. The results show that sawing stress changes smoothly during sawing process, and the fixed abrasive wire saw slicing belongs to low stress cutting way. The sawing stress at sawing kerf is increased obviously. The crystal defect leads to local stress concentration during sawing process. The coupling effect of sawing stress with initial internal stress and the effect of stress concentration are enhanced when the sawing kerf approaches to the defect.

Recently, design for additive manufacturing has been proposed to maximize product performance through the rational and integrated design of the product, its materials, and their manufacturing processes. Searching design solutions in such a multidimensional design space is a challenging task. Notably, no existing design support method is both rapid and tailored to the design process. In this study, we propose a holistic approach that applies data-driven methods in design search and optimization at successive stages of a design process. More specifically, a two-step surrogate model-based design method is proposed for the embodiment and detailed design stages. The Bayesian network classifier is used as the reasoning framework to explore the design space in the embodiment design stage, while the Gaussian process regression model is used as the evaluation function for an optimization method to exploit the design space in detailed design. These models are constructed based on one dataset that is created by the Latin hypercube sampling method and then refined by the Markov Chain Monte Carlo sampling method. This cost-effective data-driven approach is demonstrated in the design of a customized ankle brace that has a tunable mechanical performance by using a highly stretchable design concept with tailored stiffnesses.

The emerging direct four dimensional (4D) printing approach is considered as an easy, fast and economical manufacturing strategy that fabricates complex 3D geometries evolving from printed flat patterns in response to external stimuli. However, its implementation to practical engineering applications is impeded by the fact that the existing direct 4D printing methods could not render both the large bending curvature and high loading capacity at the same time. Herein, we report a multimaterial direct 4D printing method to fabricate patterned laminate that consists of covalently bonded elastomer and high-water-content hydrogel. The dehydration induced large volumetric shrinkage (up to 60%) and great modulus escalation (from 100 kPa to 4 GPa) allow the printed flat patterns to evolve into complex 3D structures with large bending curvature (up to 0.7 mm−1) and high bending stiffness (up to 104 MPa m3). To facilitate the structural design, we develop a phenomenological model to describe the dehydration induced shrinkage and stiffening, and implement this model into Euler–Bernoulli beam theory and finite element simulations. Compared with other 3D printing technologies, the proposed multimaterial direct 4D printing approach demonstrates the merits in terms of less building time and high load capacity at both room temperature and high temperature.

Bioactive synthetic scaffolds with 3D porous structure are the most attractive materials among various guided bone regeneration membranes. However, its osteogenic potential is still insufficient. This study was aimed to develop a Calcium surface-anchored Collagen I-PLGA/PCL scaffolds (PP/COL I-pDA-Ca) with enhanced osteogenicity. PP/COL I-pDA-Ca was electrospun from a collagen I-blended PLGA/PCL matrix and then modified by the chelation of Ca-ions via mussel-inspired polydopamine coating. PLGA/PCL, PLGA/PCL-polydopamine, PLGA/PCL-pDA chelated by Ca-ions were used as controls. Osteogenic effects of the scaffolds were examined using MC3T3-E1 cell culture. PP/COL I-pDA-Ca maintained 3D porous architecture with interconnected pores formed by randomly-oriented filamentous fibers and MC3T3-E1 cells cultured on it for 12 h or 24 h were more stretched and spread than those on the controls. PP/COL I-pDA-Ca significantly upregulated α10, α11 and β1 integrin expression after 48 h culture. ALP activity, OCN, OSX, BMP2 and RUNX2 expression of MC3T3-E1 cells cultured on PP/COL I-pDA-Ca scaffolds for 7 and 14 days were substantially enhanced when compared to controls (p

Three-dimensional (3D) printing has offered considerable convenience in fabricating functional structures constructed with shape memory polymers (SMPs). Conventionally, to meet the specific requirements for given applications, the shape memory property of a SMP is regulated by tailoring its molecular structure from the perspective of polymer chemistry. By virtue of the recent advances in multi-material 3D printing technology, new opportunities have emerged to customize the shape memory property from the perspective of composite material design. In this work, we propose a novel layout design strategy to 3D print multi-material composites incorporating heat-responsive SMP and flexible elastomer. Under a given volume ratio of SMP and elastomer, distinct shape memory performances are obtained for different material layouts. The underlying mechanisms are theoretically investigated based on the mechanics of composite materials and finite element (FE) simulations are conducted to provide quantitative predictions for the experimental results. As a demonstration, composites of different material layouts are used as building blocks to fabricate bilayer laminates where the incompatibility of shape fixity are pre-embedded to trigger the programmed active bending.

4D printing is a novel concept and multidiscipline research area which integrates advanced manufacturing, material science and mechanics. As an active material with high stiffness and rapid response speed, shape memory polymer (SMP) is widely used in 4D printing structures. Accordingly, a simple but effective theoretical model becomes highly desirable to better assist the 4D printing design. In this paper, a phenomenological model is developed in which the concept of phase evolution is used to describe the glass transition behavior of SMP. Explicit iterative format has been derived where the stress–strain behaviors of phase generation and phase vanishment are distinguished. The model is further employed to predict the shape memory behavior of pure SMP and active bending behavior of SMP-elastomer bilayer composites. With its inherent conciseness and generality, the model is promising to be applicable in modelling other soft active materials with phase evolution behaviors.

To understand the long-term performance degradation of asphalt, ultraviolet (UV) photo-oxidation has been used to accelerate the aging process. Three types of asphalt binders extracted from...

Shape memory polymers (SMPs) have gained strong research interests recently due to their mechanical action that exploits their capability to fix temporary shapes and recover their permanent shape in response to an environmental stimulus such as heat, electricity, irradiation, moisture or magnetic field, among others. Along with interests in conventional “dual-shape” SMPs that can recover from one temporary shape to the permanent shape, multi-shape SMPs that can fix more than one temporary shapes and recover sequentially from one temporary shape to another and eventually to the permanent shape, have started to attract increasing attention. Two approaches have been used to achieve multi-shape shape memory effects (m-SMEs). The first approach uses polymers with a wide thermal transition temperature whilst the second method employs multiple thermal transition temperatures, most notably, uses two distinct thermal transition temperatures to obtain triple-shape memory effects (t-SMEs). Recently, one of the authors’ group reported a triple-shape polymeric composite (TSPC), which is composed of an amorphous SMP matrix (epoxy), providing the system the rubber-glass transition to fix one temporary shape, and an interpenetrating crystallizable fiber network (PCL) providing the system the melt-crystal transition to fix the other temporary shape. A one-dimensional (1D) material model developed by the authors revealed the underlying shape memory mechanism of shape memory behaviors due to dual thermal transitions. In this paper, a three-dimension (3D) finite deformation thermomechanical constitutive model is presented to enable the simulations of t-SME under more complicated deformation conditions. Simple experiments, such as uniaxial tensions, thermal expansions and stress relaxation tests were carried out to identify parameters used in the model. Using an implemented user material subroutine (UMAT), the constitutive model successfully reproduced different types of shape memory behaviors exhibited in experiments designed for shape memory behaviors. Stress distribution analyses were performed to analyze the stress distribution during those different shape memory behaviors. The model was also able to simulate complicated applications, such as a twisted sheet and a folded stick, to demonstrate t-SME.

The compressive experiments on the 3D braided composites with different braiding parameters are performed in three directions (longitudinal, in-plane and transverse) at room and liquid nitrogen temperature (low as −196 °C). Macro-Fracture morphology and SEM micrographs are examined to understand the deformation and failure mechanism. The results show that the stress–strain curves and the compression properties are significantly different in the longitudinal, in-plane and transverse direction. Meanwhile, the compression properties at liquid nitrogen temperature are improved significantly than that at room temperature. Moreover, the damage and failure patterns of composites vary with the loading directions and test temperature. At liquid nitrogen temperature, the brittle failure feature becomes more obvious and the interfacial adhesion capacity is enhanced significantly. In addition, the compressive properties and failure mechanism at room and liquid nitrogen temperature can be significantly affected by the braiding angle and the fiber volume fraction.

Stretchable UV-curable (SUV) elastomers can be stretched by up to 1100% and are suitable for digital-light-processing (DLP)-based 3D-printing technology. DLP printing of these SUV elastomers enables the direct creation of highly deformable complex 3D hollow structures such as balloons, soft actuators, grippers, and buckyball electronical switches.

Conical spiral tube bundles are widely used in enhancing the heat transfer via the flow-induced vibration in heat exchangers. The shell side flow-induced vibration of the conical spiral tube bundle is experimentally investigated in this paper. The experiment table was built and the operational modes, the vibration parameters of the tube bundle were analyzed. The results show that, the operational mode frequencies of the conical spiral tube are decreased as the shell-side fluid flow velocity increases, especially for the first order frequency. Within the parameter range of this experiment, the real working frequency of the conical spiral tube is between the 1st and the 2nd operational modes, and the free end vibration amplitude of the tube bundle increases greatly when the shell side fluid flow velocity exceeds a critical value.

The information computation through synapse networks in the brain plays a vital role for cognitive behaviors such as image/video recognition, self-learning, and decision-making. Achieving proper synaptic networks by conventional semiconductor and memristive devices has encountered critical issues such as the spatial density requiring a number of transistors for one synapse, reliable filament formation in memristors, or emulating diverse excitatory and inhibitory synaptic plasticity with two-terminal device geometry. Here, we report selective growth of variously doped MoS2 with controllable conductance plasticity, which can be used for emulating diverse synaptic junctions. The conductance plasticity in the monolayer MoS2 was found to originate from resistive-heating near the junctions with electrodes in the two-terminal device geometry and the carrier concentration-dependent metal-insulator transition in the MoS2 channel. A spatiotemporal synaptic summation is demonstrated where the firing of a proper postsynaptic membrane potential can be designed for cognitive processes. Compared with previously reported three terminal synaptic devices with atomically thin materials, our two-terminal devices with flexible synaptic strengths have advantages for integrating three-dimensional neuronal networks. This provides a new insight on two-dimensional materials as a promising arena for integrated synaptic functionalities in artificial neural networks.

Shape memory polymers (SMPs) can fix a temporary shape and recover their permanent shape in response to environmental stimuli such as heat, electricity, or irradiation. Most thermally activated SMPs use the macromolecular chain mobility change around the glass transition temperature ( T g ) to achieve the shape memory (SM) effects. During this process, the stiffness of the material typically changes by three orders of magnitude. Recently, a composite materials approach was developed to achieve thermally activated shape memory effect where the material exhibits elastomeric response in both the temporary and the recovered configurations. These shape memory elastomeric composites (SMECs) consist of an elastomeric matrix reinforced by a semicrystalline polymer fiber network. The matrix provides background rubber elasticity while the fiber network can transform between solid crystals and melt phases over the operative temperature range. As such it serves as a reversible “switching phase” that enables shape fixing and recovery. Shape memory elastomeric composites provide a new paradigm for the development of a wide array of active polymer composites that utilize the melt–crystal transition to achieve the shape memory effect. This potentially allows for material systems with much simpler chemistries than most shape memory polymers and thus can facilitate more rapid material development and insertion. It is therefore important to understand the thermomechanical behavior and to develop corresponding material models. In this paper, a 3D finite-deformation constitutive modeling framework was developed to describe the thermomechanical behavior of SMEC. The model is phenomenological, although inspired by micromechanical considerations of load transfer between the matrix and fiber phases of a composite system. It treats the matrix as an elastomer and the fibers as a complex solid that itself is an aggregate of melt and crystal phases that evolve from one to the other during a temperature change. As such, the composite consists of an elastomer reinforced by a soft liquid at high temperature and a stiff solid at low temperature. The model includes a kinetic description of the non-isothermal crystallization and melting of the fibers during a temperature change. As the fibers transform from melt to crystal during cooling it is assumed that new crystals are formed in an undeformed state, which requires careful tracking of the kinematics of the evolving phases which comes at a significant computational cost. In order to improve the computational efficiency, an effective phase model (EPM) is adopted to treat the evolving crystal phases as an effective medium. A suite of careful thermomechanical experiments with a SMEC was carried out to calibrate various model parameters, and then to demonstrate the ability of the model to accurately capture the shape memory behavior of the SMEC system during complex thermomechanical loading scenarios. The model also identifies the effects of microstructural design parameters such as the fiber volume fraction.

The high temperature in grinding hardening induces workpiece thermal deformation. The thermal deformation causes a concavity on the ground profile and affects the grinding hardening depth. The paper uses ANSYS thermo-mechanical coupling module to simulate the thermal deformation in grinding hardening. The workpiece profile by simulated is compared with the test result.

The invariable heat flux is always loaded in temperature simulation for grind-hardening. The heat flux is time-variant in actual process. The paper uses experiment result of grinding force to calculate out the time variation heat flux. The grinding temperature is simulated based on time variation heat flux by ANSYS software. The variation tendencies for the grinding force and the simulated surface top temperature will be discussed.

The characteristic of flow-induced vibration and heat transfer of a cylinder with elastic supporting in two-dimensional fluid flow was numerically investigated by Workbench and CFX software. The numerical results show that, in the same conditions, the greater elastic support stiffness of the cylinder is ,the greater the value and range of fluid speed where the vortex-induced vibration of a circular occurs; With the same elastic support stiffness, the frequency and amplitude of flow-induced cylinder vibrating along transverse direction are much greater than that of in in-line direction(longitudinal direction), and the value and range of fluid speed where the vortex-induced vibration along longitudinal direction of a cylinder occurs is much smaller than that of along transverse direction. When the max vibration velocity of cylinder is much less than the flow speed, the flow-induced cylinder vibration can not reach the effect of heat transfer enhancement.

Based on the method of the statistical probability, the theory forecasting model of grinding force is modified analytically. The calculated force is used as an input factor to calculate the heat flux. Then the transient grinding temperature field is simulated using the finite element analysis (FEA). An infrared imaging system for a full area temperature measurement is used to validate the numerical model. Additionally, the experimental results are synthesized with the simulation results to analyze the temperature field and the hardness penetration depth (HPD). The distribution of the temperature field and the stability of the grind-hardening process are discussed, which could provide a reliable forecasting method for optimizing the grind process and controlling the hardening effects forwardly.

Despite great progress in four-dimensional (4D) printing, i.e. three-dimensional (3D) printing of active (stimuli-responsive) materials, the relatively low actuation force of the 4D printed structures often impedes their engineering applications. In this study, we use multimaterial inkjet 3D printing technology to fabricate shape memory structures, including a morphing wing flap and a deployable structure, which consist of active and flexible hinges joining rigid (non-active) parts. The active hinges, printed from a shape memory polymer (SMP), lock the structure into a second temporary shape during a thermomechanical programming process, while the flexible hinges, printed from an elastomer, effectively increase the actuation force and the load-bearing capacity of the printed structure as reflected in the recovery ratio. A broad range of mechanical properties such as modulus and failure strain can be achieved for both active and flexible hinges by varying the composition of the two base materials, i.e. the SMP and the elastomer, to accommodate large deformation induced during programming step, and enhance the recovery in the actuating step. To find the important design parameters, including local deformation, shape fixity and recovery ratio, we conduct high fidelity finite element simulations, which are able to accurately predict the nonlinear deformation of the printed structures. In addition, a coupled thermal-electrical finite element analysis was performed to model the heat transfer within the active hinges during the localized Joule heating process. The model predictions showed good agreement with the measured temperature data and were used to find the major parameters affecting temperature distribution including the applied voltage and the convection rate.

Based on reciprocating electroplated diamond wire saw (REDWS) slicing experiments, a study on REDWS machining brittle-ductile transition of single crystal silicon was introduced. The machined surfaces and chips were observed by using Scanning Electron Microscope (SEM), and some experimental evidences of the change of material removal mode had been obtained. The experimental results indicate there is a close relationship between material removal mode and the ratio r value of ingot feed speed and wire speed, through controlling and adjusting the r value, the material removal mode can be complete brittle, partial ductile and near-ductile removal.

The hardening characteristics could be achieved by a proper selection of the grinding conditions. It is necessary to keep the heat flux above the critical limit for the film-boiling and the austenitization within the grinding zone. In this paper, a critical thermal analysis was presented to calculate the critical heat flux, following the methods for predicting thermal damages in creep grinding and high efficient grinding. The appearances of the hardening phenomena were predicted for dry grinding and wet grinding. It also can guide the selection of the grinding conditions. Theoretical analysis was verified by the experiments. Measurements are found to be in good agreement with the theoretical predictions.

The grind-hardening technology utilizes the grinding heat to harden the surface of the workpiece. The friction and wear performance of the grind-hardened layer is one of the important parameters. In this paper, the friction and wear performance of the grind-hardened layer was studied by the friction and wear experiment. The wear rate and the friction coefficient of the grind-hardened steel were studied by comparing with conventional hardened steel and non-hardened steel. The surface worn morphology and the collected wear debris of the grind-hardened steel were observed during the experiment. The wear mechanism of the grind-hardened steel was analyzed under different friction conditions.

The leak detection of rockfill dams is currently hindered by spatial and temporal randomness and wide monitoring range. The spatial resolution of fiber Bragg grating (FBG) temperature sensing technology is related to the distance between measuring points. As a result, the number of measuring points should be increased to ensure that the precise location of the leak is detected. However, this leads to a higher monitoring cost. Consequently, it is difficult to promote and apply this technology to effectively monitor rockfill dam leakage. In this paper, a practical mobile distributed monitoring system with dual-tubes is used by combining the FBG sensing system and hydrothermal cycling system. This dual-tube structure is composed of an outer polyethylene of raised temperature resistance heating pipe, an inner polytetrafluoroethylene tube, and a FBG sensor string, among which, the FBG sensor string can be dragged freely in the internal tube to change the position of the measuring points and improve the spatial resolution. In order to test the effectiveness of the system, the large-scale model test of concentrated leakage in 13 working conditions is carried out by identifying the location, quantity, and leakage rate of leakage passage. Based on Newton's law of cooling, the leakage state is identified using the seepage identification index ζ v that was confirmed according to the cooling curve. Results suggested that the monitoring system shows high sensitivity and can improve the spatial resolution with limited measuring points, and thus better locate the leakage area. In addition, the seepage identification index ζ v correlated well with the leakage rate qualitatively.

Because its advantages of lower manufacture cost and higher slicing quality, the resin bonded diamond wire saw is supposed to be used widely in the future for slicing hard-brittle materials such as silicon crystal. In this paper, based on the research of the resin bonded diamond wire saw manufacturing technology and slicing process, we select Φ0.2mm SWPB piano string as core wire, 20-30m (800#) diamond grain as abrasive, liquid phenolic resin mixed with epoxy resin as adhesive, the nanometer powders as additive to improve the adhesive holding strength of abrasive grains and heat resistance. By orthogonal experiment, we find the resin bonded diamond wire saw has optimizing performance as the additives is 10% in adhesive, the epoxy resin is 30% in resin, the diamond is 50% in whole mixed material. Slicing experiments proves that the resin bonded diamond wire saw manufactured in this study has better slicing performance. The failure forms of the resin bonded diamond wire saw are wear out of resin adhesive, falling off of diamond grains and the partial peeling off of the resin bond.

Based on reciprocating electroplated diamond wire saw slicing single crystal silicon experiments, a bonded interface sectioning technique was used to measure the silicon subsurface damage (SSD) depth, and the influences of wire saw speed and feed speed on silicon SSD were studied. Moreover, based on the indentation fracture mechanics (IFM) theory, a theoretical model of relationship between SSD and surface roughness (SR) was established for predicting the SSD depth by measuring the SR. The results indicate that SSD depth decreases with the wire saw speed increase and feed speed decrease, within the range of experimental technical parameters. There exists monotone increasing non-linear correlation between SSD depth and SR (Rz) in wire saw slicing single crystal silicon, that is, SSD－SR+χSR3/4. And the experimental measure values coincide with the theoretical prediction values comparatively, therefore, the theoretical model can be used for predicting SSD depth rapidly, expediently and accurately.

Development of high performance diamond impregnated wire is the key of application for fixed-abrasive wire sawing technology. In this paper, some experimental studies were done for development of electroplated diamond wire saw by employing the bright nickel bath. The wire saw electroplating process was developed, the effects of cathode current density and time at tack-on stage on diamond grits density and adhesion between saw matrix and plating coating were discussed. The wire saw cutting experiments were carried out for analysis the used wire wear using the scanning electron microscope (SEM). The experimental results show the optimum tack-on current density to obtain the wire saw with good abrasive distribution and adhesion is 1.5~2.0A/dm2, and the time of pre-plating, tack-on and buildup is 6, 8~10 and 18min in turn. Diamond wire saw wear includes coating wear and grain-abrasion, and the primary wear form is grits pulled-out.