Mechanics of Time-Dependent Materials最新文献

Thin-laminate composites with thicknesses below 200 μm hold significant promise for future, larger, and lighter deployable structures. This paper presents a study of the time-dependent failure behavior of thin carbon-fiber laminates under bending, focusing on establishing a fundamental material-level understanding of this type of failure. A novel test method was developed, enabling in-situ micro-CT imaging during long-term bending. Time-to-rupture experiments revealed the stochastic nature of failure, prompting a statistical approach to account for initial imperfections. The total probability of failure was calculated using separate Weibull functions for instantaneous and delayed time-dependent failures. The resulting function, dependent on curvature and aging time, is a design guideline for the design of future deployable space structures. Time-lapse micro-CT imaging identified kink bands and fiber–matrix debonding as primary failure mechanisms, providing essential insights for the design optimization of composite laminates.

Within the framework of fractional-order thermoelasticity, the propagation of elastic waves in non-local isotropic rotating medium has been considered. The frequency dispersion relation is derived by solving the governing equations in the (xy)-plane for the given problem. Three coupled quasi-waves have been seen to move through this kind of medium at different rates. The Helmholtz decomposition theorem has been used to decompose the system into longitudinal and transverse components. Analytical computations are made for the waves’ related amplitude ratios and their speed. The amplitude ratios for the reflected waves are computed with the help of suitable boundary conditions. The impact of fractional order, rotational frequency, and non-local parameters on propagation speed and amplitude ratios has been studied and the same has been plotted graphically. In the absence of rotation, the prior findings mentioned in the literature are obtained as a specific case.

In this investigation, we conducted graded creep cyclic loading and unloading testing to measure the viscoelastic-plastic rheological properties of red sandstone from Southern China under acidic conditions. We utilized an enhanced method to divide the strain into four components: instantaneous elastic strain, instantaneous plastic strain, viscoelastic strain, and viscoplastic strain. We analyzed the strain characteristics of the corroded samples in relation to the deformation modulus. Employing nonlinear rheological theory, we derived the constitutive equations for creep damage in rock under both one-dimensional and three-dimensional stress states. Our findings indicate that acid corrosion has a minimal impact on the resistance to elastic deformation in red sandstone, with the elastic deformation modulus remaining relatively unchanged at comparable stress levels. The relationships between instantaneous elastic strain and viscoelastic strain with deviatoric stress are nearly linear. Increased acidity enhances the plastic deformation of the sandstone, marked by a progressive increase in the instantaneous plastic modulus and a decrease in instantaneous plastic strain increments with successive loading and unloading cycles. The viscoplastic modulus decreases as stress levels rise, leading to increased viscoplastic strain. Incorporating a chemical damage variable that accounts for plastic deformation, we established a creep damage constitutive equation that separates viscoelastic-plastic strains. The validity and accuracy of our proposed model are confirmed through comparison with the traditional Nishihara model.

The recent availability of a wide range of additively manufactured materials has facilitated the translation from prototype-limited to application-ready 3D printed components. As such, additively manufactured materials deployed in dynamic environments require extensive characterization to elucidate and optimize performance. This research evaluates the dynamic response of fused filament fabrication and vat photopolymerization printed polymers as a function of temperature. Dynamic mechanical analysis is used to extract the viscoelastic properties of several generations of samples exhibiting a range of thermomechanical behavior, highlighting the stiffness and damping characteristics. A modified stiffness–temperature model supports the experimental characterization and provides additional insight concerning the molecular motion occurring over each thermal transition. The insights from the analysis were collated into a case study that leverages their dynamic characteristics in a multimaterial application. The outcomes from this research assimilate a framework that defines the temperature operating range and broadens the design envelope for these additive manufacturing materials.

This article explores the memory effects of a three-dimensional cylindrical panel with a void using the Three-Phase-Lag (3PL) theory. The study derives the governing equations for displacement, temperature, void volume fraction, and stress. These equations are solved using Fourier–Laplace transforms and eigenvalue methods. To obtain numerical solutions and generate graphical representations, the transformed equations were inverted. Material properties from Gauthier’s work were used, and graphical results were produced using Mathematica software. The influence of memory response is then demonstrated by comparing kernel functions and time delay parameters within the 3PL porous cylindrical panel. The results show significant changes in the behavior of the panel. The validity of the proposed model is confirmed by comparing its predictions with previously published findings. The authors believe these results can provide valuable insights for various engineering applications involving porous materials. The model allows for accurate prediction of material behavior under different loading conditions, leading to a deeper understanding of various kernel phenomena.

This paper attempts to evaluate the influence of strain rate on the debonding stress of the spherical nanoparticles using a closed form solution. A coherent model to correlate a relationship between the debonding stress of polymer-based nanocomposites and the strain rate was developed. A representative volume element (RVE) containing a spherical nanoparticle, an interphase material, and a pure polymer phase was regarded. A relationship between the debonding stress and the applied strain rate, the material, and geometrical properties of the RVE’s constituents was correlated. In addition to the strain rate, the role of some effective variables such as nanoparticles size, interphase thickness, and interphase stiffness on the debonding stress were investigated. To evaluate the model, three case studies based on the experimental studies performed on silica nanoparticles/epoxy, CaCO₃ nanoparticles/high-density polyethylene (HDPE), silica nanoparticles/photopolymer nanocomposites were conducted. For the nano-silica/epoxy system, the results revealed that by enhancing the strain rate, the normalized debonding stress decreases. Additionally, under a certain strain rate, the normalized debonding stress enhances as much as the stiffness of interphase material increases and the nanoparticle size decreases. In the case of CaCO₃/HDPE nanocomposites, it was observed that by increasing the size of nanoparticles, the normalized debonding stress was reduced significantly. For the nano-silica/photopolymer nanocomposites, it was found that the dependence of the normalized debonding stress on the strain rate is more remarkable for the thicker interphase region. The proposed model can be used to predict the mechanical properties of nanoparticles/polymer systems under high strain rate conditions.

This research formulates a nonlocal systemic model to integrate viscoelastic and thermal deformations in solid structures based on fractional thermo-viscoelasticity theory. This enhanced model offers a more comprehensive understanding by integrating several existing theories. We apply the model to a one-dimensional problem involving a micro-rod made of an electrically conductive polymer, heated by a moving heat source. The analysis employs Laplace transforms with numerical inversion to determine the effects of fractional order, nonlocal elasticity, and nonlocal thermal conduction on thermal dispersion and the thermoviscoelastic response. Comparative figures illustrate the impact of an applied magnetic field. Results show that nonlocal thermal and viscoelastic parameters significantly influence all measured field values, potentially providing guidelines for the design and analysis of thermal-mechanical features in nanoscale devices.

This study investigated the long-term creep behavior of concrete in drilled shafts using conventional and soft-cutting head techniques, focusing on their propensity for internal defects and crack propagation under sustained loading. Triaxial creep tests were performed on concrete specimens subjected to multistage loading to examine the axial- and radial-creep responses associated with each cutting-head method. The findings reveal that concrete prepared with conventional cutting heads exhibits a higher susceptibility to creep failure, attributed to an increased presence of internal defects. In contrast, specimens using soft-cutting heads demonstrated reduced axial- and radial-creep deformations. Concrete cured in laboratory conditions and those cut with soft-cutting heads at various elevations predominantly experienced shearing failures, whereas specimens with soft-cutting heads positioned at higher elevations were more prone to radial tension-shear failures. Considering the Burgers model and fractional-order theory, we introduce a one-dimensional nonlinear damage creep model, alongside a more comprehensive three-dimensional damage creep model. Validation of these models confirms their effectiveness in describing the creep behavior of concrete under different cutting-head disturbances. Importantly, our analysis suggests that the role of soft-cutting head methods on the integrity of cast-in-place concrete piles is comparatively minimal. This insight underscores the potential for optimizing pile-head breaking techniques to mitigate creep-related failures in concrete structures.

Higher reclaimed asphalt pavement (RAP) in asphalt mixtures requires efficient rejuvenation. The efficiency of the rejuvenation can be evaluated by studying the rejuvenator, new and old binder blend. The blend must represent the binder blend inside the asphalt mixture to reflect reality. Extracting and recovering the binder of the rejuvenated asphalt mixtures containing RAP is the best practice to obtain the binder blend inside the asphalt mixture. However, extraction and recovery is not a common practice to study rejuvenation efficiency since it is time-consuming and energy-demanding with exposure to hazardous chemicals. Instead, blending rejuvenator, new binder and the extracted and recovered (E&R) binder from RAP limits the extraction and recovery to the RAP and minimizes efforts for studying rejuvenation efficiency. This study aims to find the blending conditions under which the blend of the rejuvenator, new and RAP binder represents the E&R binder from asphalt mixture concerning rheological performance and behavior properties. The rheological properties of three binder blends prepared under intense, moderate, and low blending conditions were compared with those of the E&R binder. Performance grade (PG), rutting potential (multiple stress creep and recovery test), fatigue resistance (linear amplitude sweep test) and behavioral characteristics (linearity and complex modulus tests) are the rheological properties of this study. It was found that intense and moderate blending conditions are good representatives of the E&R binder with regard to PG and PG+ designation. In addition, intense, moderate, and low blending conditions can be a surrogate for the PAV-aged E&R binder. It can be claimed that any intensity of blending conditions between intense and moderate lead to binder specimen that is almost identical to E&R binder with respect to rutting potential and characterization.

Ultrasonic vibration-assisted grinding (UVAG) enhances surface integrity in machined parts, especially in achieving greater compressive residual stress. Typically, the calculation of residual stresses in UVAG relies on generic finite element software that is not optimized for this purpose, suffering from cumbersome modeling and inefficient calculations. This paper introduces a numerical-analytical hybrid model tailored to predict residual stresses in UVAG. The model independently calculates mechanical and thermal stress fields using contact mechanics and finite difference methods. It employs Hertz’s contact theory and Timoshenko’s thermoelastic theory to establish a correlation between mechanical and thermal loads and the internal stresses in the workpiece. The residual stress field is then determined by considering the thermal-mechanical coupling effects inherent in UVAG. Experiments conducted on 12Cr2Ni4A alloy steel validate the model, with a maximum deviation of 10.5% between predicted and measured residual stresses. Further analysis shows that the presented method has a significant computational efficiency advantage over the simulation method that uses generic finite element software. The work confirms the accuracy and efficiency of the proposed model, offering a novel approach for predicting residual stress in UVAG.