查看更多>>摘要：Elasto-capillarity phenomena are prevalent in various industrial fields such as mechanical engineering,material science,aerospace,soft robotics,and biomedicine.In this study,two typical peeling processes of slender beams driven by the parallel magnetic field are investigated based on experimental and theoretical analysis.The first is the adhesion of two parallel beams,and the second is the self-folding of a long beam.In these two cases,the energy variation method on the elastica is used,and then,the governing equations and transversality boundary conditions are derived.It is shown that the analytical solutions are in excellent agreement with the experimental data.The effects of magnetic induction intensity,distance,and surface tension on the deflection curve and peeling length of the elastica are fully discussed.The results are instrumental in accurately regulating elasto-capillarity in structures and provide insights for the engineering design of programmable microstructures on surfaces,microsensors,and bionic robots.
查看更多>>摘要：Microcracks are common in compact bone,but their continued propagation can lead to macroscopic fractures.These microc-racks cannot be visualized radiographically,necessitating alternative noninvasive methods to identify excessive microcracking and prevent fractures.In this study,terahertz time-domain spectroscopy(THz-TDS)was used to examine bone interiors near cracks resulting from loading in bovine tibia samples.Various loading configurations,such as impact,quasi-static loading,and fatigue loading,known to induce different types of micro-scale damage,were applied.The values of refractive index and absorption coefficient of the bone samples were then determined from the THz-TDS spectra acquired before loading and after fracture.The study revealed that different loading configurations led to varying terahertz optical coefficients associated with various types of bone fractures.Specifically,the refractive index notably increased under fatigue loading but remained relatively stable during quasi-static bending.The absorption coefficient of bone decreased only under fatigue loading.Further-more,samples were subjected to axial and radial impacts without sustaining damage.Results indicated that in the undamaged state,the change in refractive index was smaller compared to after impact failure,while the change in absorption coefficient remained consistent after failure.Under radial impact loading,changes in refractive index and absorption coefficient were significantly more pronounced than under axial loading.Prior to loading,the measured value of refractive index was 2.72±0.11,and the absorption coefficient was 6.33±0.09 mm-1 at 0.5 THz.
查看更多>>摘要：This paper intensively explores the critical issues related to the quantitative and accurate evaluations of FCG behavior in the early stage,macro fatigue fracture toughness,and the critical crack size for damage tolerance in nuclear graphite.To address these issues,scale-span FCG tests were carried out using two typical specimens,CT and SEM in-situ specimens.These results indicate that the FCG threshold and the effective FCG length have a significant correlation with the modified maximum loop stress theory for a mixed Ⅰ/Ⅱ mode.In particular,the effective FCG length(aeq)and the applied stress threshold of polycrystalline graphite are important parameters for fatigue damage tolerance design in engineering application.The influencing factors of ΔKth.eq and aeq were discussed in detail using the mixed Ⅰ/Ⅱ mode,respectively.In addition,the scattered values of ΔKIC for this graphite can be quantitatively estimated using the Weibull distribution equation.The predicated parameters and experimental results demonstrate a strong correlation.
查看更多>>摘要：For fragile products,packaging requires cushioning protection to prevent irreversible damage from accidental falls,transporta-tion impacts,and other causes.The new polyurethane foam(PUF)material demonstrates superior cushioning and vibration isolation performance in practical applications,effectively minimizing damage from vibrations.Drop and vibration experi-ments were conducted on packages comprising novel PUF,expandable polyethylene,ethylene-vinyl acetate copolymer foam,and bracelets.Results verify that the new PUF material outperforms in cushioning and vibration isolation,as observed from the acceleration response.Furthermore,a random vibration analysis of a packaging unit involving different thicknesses of PUF materials and bracelets reveals the enhanced vibration isolation effect within a specific thickness range.The vibration results of the bracelet's outer packaging align closely with finite element simulation results,validating the effectiveness of designing and optimizing the outer packaging.Through finite element simulation,deeper understanding and prediction of the bracelet's vibration response under various conditions is achieved,facilitating optimized packaging design for better protection and vibration damping.
查看更多>>摘要：Structural damage detection(SDD)remains highly challenging,due to the difficulty in selecting the optimal damage features from a vast amount of information.In this study,a tree model-based method using decision tree and random forest was employed for feature selection of vibration response signals in SDD.Signal datasets were obtained by numerical experiments and vibration experiments,respectively.Dataset features extracted using this method were input into a convolutional neural network to determine the location of structural damage.Results indicated a 5％to 10％improvement in detection accuracy compared to using original datasets without feature selection,demonstrating the feasibility of this method.The proposed method,based on tree model and classification,addresses the issue of extracting effective information from numerous vibration response signals in structural health monitoring.
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