High-accuracy virtual testing of air conditioner's digital twin focusing on key material's deformation and fracture behavior prediction.

The concept of digital twin has been introduced for some time, yet one fundamental element of digital twin, digital material, has not been thoroughly studied. To interact with the physical product, the digital twin should always truthfully reflect the responses under various stimuli. In this paper, the deformation and fracture behavior of high impact polystyrene (HIPS) under the influencing factors of strain rate and stress triaxiality are studied to construct the material's digital model. A digital twin of air conditioner product is further built and tested under virtual drop test. Comparing to experimental results, the acceleration curve, crazing induced whitening and the fracture events can all be captured by the digital twin. Our work demonstrates the importance of material characterization as an essential step to construct an accurate digital twin and shows a promising future of digital twin in virtual testing to replace traditional "trial and error" experiments.

Experimental and Numerical Investigation on the Effect of Scratch Direction on Material Removal and Friction Characteristic in BK7 Scratching.

In order to study the influence of scratch direction on the deformation characteristics and material removal mechanism of optical glass BK7, nanoscratching experiments were conducted on a Nano indenter using Vickers indenter. Results indicate that the face-forward scratch is more likely to induce the initiation and propagation of lateral cracks, which is found to be more beneficial to material removal processes; in contrast, small chips and debris are released from the machined grooves without introducing lateral cracks in the edge-forward condition, leading to poor material removal efficiency. In addition, the choice of scratch direction can make differences to the elastic recovery rate of optical glass BK7. The results revealed that both the elastic recovery rate and the residual stresses of the material under the face-forward scratching are greater than those of the edge-forward scratching. A theoretical model for coefficient of friction (COF) under different scratch directions was established. It is found that the COF between indenter and workpiece in the edge-forward scratching is larger than the face-forward scratching under otherwise identical conditions, this finding is consistent with experimental results. A stress field analysis using finite element method (FEM) was conducted to understand the different crack initiation and propagation behaviors from different scratch directions. The current study discusses the significance of scratch direction on material removal behavior of optical glass BK7, and the results would encourage further research on investigating the connections between tool geometry and material removal mechanism.

Finite element analysis for mechanics of guiding catheters in transfemoral intervention.

BACKGROUND: During the percutaneous coronary intervention (PCI), the strong backup support of a guiding catheters is essential in reaching a target coronary lesion successfully. Nevertheless, it is difficult to explore the mechanics of a guiding catheter by analytical and experimental methods due to its complex deformation and interactions among guiding catheter, guide wire, and artery. In this study, the finite element method was used to analyze the backup support of a guiding catheter in transfemoral intervention (TFI). METHODS: A finite element model was established in the light of geometric, mechanical properties of the guiding catheter and boundary con ditions. To validate the finite element model, an arterial tree model was constructed to measure the backup force of the guiding catheters in TFI. Then, the process of the guiding catheter disengaged from the ostium was analyzed. RESULTS: The influencing rules of the geometric parameters of the guiding catheter on its backup support in TFI were obtained with the help of the finite element model. The result shows that the larger the outer diameter and wall thickness, the greater the backup support, 2.0 to 2.3 mm of the outer diameter was suggested. When designing a guiding catheter, it is wise to avoid α, the angle between the line and wall of the artery, being within 60° and 75° and it is a better choice if the contact length is between 5 and 12 mm. CONCLUSIONS: This study sought to investigate the influencing rules of the geometric parameters of the guiding catheter on its backup support in transfemoral intervention. A finite element model for analyzing the backup support of a guiding catheter was validated by experiments. It indicated that the finite element method can analyze the varied laws of the guiding catheter with different geometric parameters.

Fabrication and Characteristics of Sintered Cutting Stainless Steel Fiber Felt with Internal Channels and an Al2O3 Coating.

A novel sintered cutting stainless steel fiber felt with internal channels (SCSSFFC) composed of a stainless-steel fiber skeleton, three-dimensional interconnected porous structure and multiple circular microchannels is developed. SCSSFFC has a jagged and rough surface morphology and possesses a high specific surface area, which is approximately 2.4 times larger than that of the sintered bundle-drawing stainless steel fiber felt with internal channels (SBDSSFFC) and is expected to enhance adhesive strength. The sol-gel and wet impregnation methods are adopted to prepare SCSSFFC with an Al2O3 coating (SCSSFFC/Al2O3). The adhesive strength of SCSSFFC/Al2O3 is investigated using ultrasonic vibration and thermal shock tests. The experimental results indicate that the weight loss rate of the Al2O3 coating has a 4.2% and 8.42% reduction compared with those of SBDSSFFCs based on ultrasonic vibration and thermal shock tests. In addition, the permeability of SCSSFFC/Al2O3 is investigated based on forced liquid flow tests. The experimental results show that the permeability and inertial coefficients of SCSSFFC/Al2O3 are mainly affected by the coating rate, porosity and open ratio; however, the internal microchannel diameter has little influence. It is also found that SCSSFFC/Al2O3 yields superior permeability, as well as inertial coefficients compared with those of other porous materials reported in the literature.

A Thermoplastic Multilayered Carbon-Fabric/Polycarbonate Laminate Prepared by a Two-Step Hot-Press Technique.

Carbon fiber (CF) reinforced thermoplastic composites have gradually become increasingly popular in composite production owing to their lower hazard level, good structural flexibility and recyclability. In this work, a multilayered carbon⁻fabric/polycarbonate laminate (multi-CFPL) was fabricated by a two-step hot-press process, mainly based on the thermoplastic properties of its polycarbonate (PC) matrix. Different from the conventional one-step method, the two-step hot-press process was composed of two separate procedures. First, a unit-hot-press operation was introduced to prepare a single-layered carbon⁻fabric/PC laminate (simplified as unit-CFPL). Subsequently, a laminating-hot-press was employed to compress several as-prepared unit-CFPLs bonded together. This combined process aims to reduce the hot-press temperature and pressure, as well as facilitate the structure designability of this new composite. Several mechanical investigations were conducted to analyze the effect of the hot-press parameters and unit-CFPL numbers on the performance of this multi-CFPL material, including flexural, uniaxial tensile and impact tests. The results reveal that the multi-CFPL exhibits a good stability of flexural and tensile properties in terms of strength and modulus. Furthermore, during impact tests, the multi-CFPL presents an accelerated growth of peak force and energy absorption capability with increasing unit-CFPL layers.

A Performance-testing Platform for a Conduction Micropump with an FR-4 Copper-clad Electrode Plate.

Here, a conduction micropump with symmetric planar electrode pairs prepared on flame-retardant glass-reinforced epoxy (FR-4) copper-clad laminate (CCL) is fabricated. It is used to investigate the influence of chamber dimensions on the performance of a conduction micropump and to determine the reliability of the conduction pump when acetone is used as the working fluid. A testing platform is set up to evaluate conduction micropump performance under different conditions. When the chamber height is 0.2 mm, the pump pressure reaches its peak value.

The Electrochemical Behavior of Carbon Fiber Microelectrodes Modified with Carbon Nanotubes Using a Two-Step Electroless Plating/Chemical Vapor Deposition Process.

Carbon fiber microelectrode (CFME) has been extensively applied in the biosensor and chemical sensor domains. In order to improve the electrochemical activity and sensitivity of the CFME, a new CFME modified with carbon nanotubes (CNTs), denoted as CNTs/CFME, was fabricated and investigated. First, carbon fiber (CF) monofilaments grafted with CNTs (simplified as CNTs/CFs) were fabricated in two key steps: (i) nickel electroless plating, followed by (ii) chemical vapor deposition (CVD). Second, a single CNTs/CF monofilament was selected and encapsulated into a CNTs/CFME with a simple packaging method. The morphologies of as-prepared CNTs/CFs were characterized by scanning electron microscopy. The electrochemical properties of CNTs/CFMEs were measured in potassium ferrocyanide solution (K4Fe(CN)6), by using a cyclic voltammetry (CV) and a chronoamperometry method. Compared with a bare CFME, a CNTs/CFME showed better CV curves with a higher distinguishable redox peak and response current; the higher the CNT content was, the better the CV curves were. Because the as-grown CNTs significantly enhanced the effective electrode area of CNTs/CFME, the contact area between the electrode and reactant was enlarged, further increasing the electrocatalytic active site density. Furthermore, the modified microelectrode displayed almost the same electrochemical behavior after 104 days, exhibiting remarkable stability and outstanding reproducibility.

Experimental Study on Tensile Properties of a Novel Porous Metal Fiber/Powder Sintered Composite Sheet.

A novel porous metal fiber/powder sintered composite sheet (PMFPSCS) is developed by sintering a mixture of a porous metal fiber sintered sheet (PMFSS) and copper powders with particles of a spherical shape. The characteristics of the PMFPSCS including its microstructure, sintering density and porosity are investigated. A uniaxial tensile test is carried out to study the tensile behaviors of the PMFPSCS. The deformation and failure mechanisms of the PMFSCS are discussed. Experimental results show that the PMFPSCS successively experiences an elastic stage, hardening stage, and fracture stage under tension. The tensile strength of the PMFPSCS is determined by a reticulated skeleton of fibers and reinforcement of copper powders. With the porosity of the PMFSS increasing, the tensile strength of the PMFPSCS decreases, whereas the reinforcement of copper powders increases. At the elastic stage, the structural elastic deformation is dominant, and at the hardening stage, the plastic deformation is composed of the structural deformation and the copper fibers' plastic deformation. The fracture of the PMFPSCS is mainly caused by the breaking of sintering joints.