查看更多>>摘要：In this paper,the degradation of mechanical properties of engineering cementitious composites(ECCs)at elevated temperatures and the failure of fiber are considered.A failure model under coupled thermo-mechanical loads for ECC is developed based on bond-based peridynamics.A semi-discrete model is constructed to describe fiber-matrix interactions and simulate thermal failure in ECC.The peridynamic differential operator(PDDO)is utilized for non-local modeling of thermal fluid flow and heat transfer.A multi-rate explicit time integration method is adopted to address thermo-mechanical coupling over different time scales.Model validation is achieved through simulating transient heat transfer in a homogeneous plate,with results aligning with analytical solutions.The damage behavior of a heated ECC plate in a borehole and under a fire scenario is analyzed,providing insights for enhancing fire resistance and high-temperature performance of ECC materials and structures.
查看更多>>摘要：Adiabatic shear band(ASB),a typical failure mechanism in a metal at high strain rates,is hardly controllable or predictable to some extent.The development of the microstructure plays a crucial role in its formation.In this paper,the effect of strain rate on the development of microstructure in ASB of titanium alloy TC4 is investigated using hat-shaped specimens with the split-Hopkinson pressure bar device.The results show that the fracture strength of TC4 is significantly dependent on the shear strain rate.The increase in fracture strength from a strain rate of 11,300 s-1 to 24,930 s-1 is much higher than that from 24,930 s-1 to 35,620 s-1,which can be attributed to the effect of strain rate on dislocation evolution.Microstructures in both as-received and deformed states are investigated using various characterization techniques such as electron backscatter diffraction and X-ray diffraction.The region of ASB clearly shows three different microstructural features:random distribution of coarse grains(as received),distribution of elongated grains(transition zone),and distribution of equiaxed nanocrystals(shear-localized zone).The width of ASB increases with the strain rate.The possible reason for this is that the higher the strain rate,the larger the region where dynamic recrystallization(DRX)occurs due to the accumulation of a large number of dislocations.In the middle of ASB,a significant decrease in low-angle grain boundaries(LAGBs)and a large increase in high-angle grain boundaries are observed.The texture of specimens,especially the {11-20} and {10-10} planes,changes significantly during shear deformation at high strain rates.The mechanism of continuous dynamic recrystallization can well explain the formation and evolution of DRX within the ASB.
查看更多>>摘要：The tubular Miura-ori(TMO)structure has attracted much attention due to its excellent folding capability and rich application diversity.However,the existing theoretical research on origami structure is overly complex,and kinematic analysis rarely involves bending motion.In the present work,based on geometric kinematics,"equivalent deformation mechanism"is proposed to study the axial and bending motions of TMO under small in-plane deformations.Firstly,the geometric design is studied using the vector expression of creases.To simplify the kinematic analysis of axial motion,TMO deformation is equated to a change in angle.The proposed method is also applicable to bending motion,because both bending and axial motions can be described using similar deformation mechanisms.In addition,the accuracy of the proposed method is validated through numerical analysis,and the error between analytical and numerical solutions is sufficiently small for the folding angleγ ∈[25°,65°].Finally,the numerical simulation is validated with mechanical experiments.Results show the effectiveness of the proposed method in describing the kinematic law of TMO structures in a simple way.This research sheds light on the kinematic analysis of other origami structures and establishes a theoretical framework for their applications in aerospace engineering,origami-based metamaterials,and robotics.
查看更多>>摘要：In this work,a tacticity strategy is proposed to adjust the mechanical properties of chiral mechanical metamaterials for vibration isolation.By applying the finite element method,the impact of tacticity on tensile deformations,band structures,and vibration transmission spectra of chiral metamaterials is investigated.The axial deformations of isotactic configuration and syndiotactic configuration are similar under tensile loads,but rotational deformation occurs in the isotactic configuration.With the same geometric and material parameters,the first band gap of the syndiotactic configuration is lower than that of the isotactic configuration.The vibration suppression performance of chiral mechanical metamaterials is verified by numerical simulations and experiments.Parametric analysis of the band gap provides valuable insights for the manipulation and expansion of vibration reduction.Gradient design based on parametric analysis achieves an extended range of vibration suppression.
查看更多>>摘要：In micro-electro-mechanical systems,interface expansion issues are commonly encountered,and due to their small size,they often exist at the micro-or nano-scale.The influence of the micro-structural effect on interface mechanics cannot be ignored.This paper focuses on studying the impact of micro-structural effect on interface crack propagation.Modified couple stress theory(MCST)is used to study the buckling delamination of ultra-thin film-substrate systems.The equivalent elastic modulus(EEM)and equivalent flexural rigidity(EFR)are derived based on MCST.Substituting EEM and EFR into the classical Kirchhoff plate theory,the governing equations of ultra-thin film-substrate system with micro-structural effect can be obtained.The finite element method(FEM)was used to calculate the critical strain energy release rate for crack extension.Differences between the three theoretical approaches of MCST,classical theory(CT),and FEM were compared.The effects of stress ratio σ/σc,initial crack length,film thickness,and micro-structural effect parameters on crack extension were analyzed.The results show that the FEM calculations coincide with the CT calculations.The stress ratio σ/σc,initial crack length,film thickness,and micro-structural effect parameters have significantly influence crack extension.
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