To investigate the structural integrity of solid propellant under low temperature ignition impulsion conditions, this paper employs the generalized nonlinear Zhu-Wang-Tang (ZWT) constitutive model with four Maxwell elements, where the parameters of the constitutive model are obtained combining the tensile test data and slime mold algorithm (SMA). Based on the secondary development function of UMAT of the ABAQUS finite element analysis software, this constitutive model is then adopted to numerically simulate the propellant uniaxial tensile test under constant strain. The simulation results were compared with experimental data to validate the reliability of the numerical simulation method. Finally, this numerical simulation method is used to study the structural integrity of 5-pointed star HTPB solid propellant under curing cooling and ignition impulsion conditions at −30°C. The results show that the SMA has faster convergence and higher accuracy than commonly used ant colony optimization. The uniaxial tensile simulation results of the propellant under constant strain are consistent with the experimental results, which verifies the dependability of the constitutive model and the numerical simulation method. The HTPB solid propellant under the conditions of curing cooling and ignition impact at different ignition pressures (10, 12, 15, and 20 MPa) is also applicable to the HTPB solid propellant under different ignition pressures. The maximum equivalent stress and equivalent strain values of HTPB solid propellant under curing cooling and different ignition impulsion pressures (10, 12, 15, and 20 MPa) all appeared at the transition arc of the grain. The structural integrity of the grain is not damaged within 20 MPa ignition pressure at a low temperature of −30°C.

Compression tests employing small, non-standard specimens face challenges in accurate displacement measurement due to the unsuitability of contact extensometers and the high cost/complexity of video extensometers. The objective of this study is to develop a method for accurately measuring the true displacement of specimens during compression testing without the use of extensometers. Finite element analysis and compression tests on specimens with known elastic moduli identified three error components: frame deformation, contact gaps, and strain concentration at the fixture-specimen interface. Contact gaps can be eliminated through light preloading, leaving residual errors (denoted as Y) from frame compliance and interface strain concentration. Y was quantified by compressing small-diameter specimens of high-strength materials with known elastic moduli, specifically WC-11%Co cemented carbide, which was used in this study. The relationship between Y, load, and specimen diameter was established by subtracting the actual deformation of the small-diameter specimen from the total machine-recorded displacement. Subsequently, true specimen displacement was obtained by subtracting Y from the measured displacement. The method was validated on six metallic materials (Ni, W, Mo, Cu, Ti, #45 steel). Corrected stress-strain curves reduced elastic modulus errors to blow 10%. For example, Ni’s modulus improved from 26.5 GPa (uncorrected) to 195.4 GPa (96.7% of the true value), and W’s modulus increased from 34.2 to 370.2 GPa (92.6% of the true value). The proposed method requires only a single calibration test for specimens of identical diameter to establish Y-load-diameter mappings. Once integrated into testing systems, true displacement can be directly obtained, offering a cost-effective and operationally simple solution for small-specimen compression testing.

In this study, a simple mechanical model was established using infinitesimal method to investigate the tensile strength of a novel sisal hemp/PET filament island phase structure composite rope core yarn with improved mechanical properties comparing with the traditional sisal hemp rope core yarn. The result revealed that the tensile strength of the composite rope core yarns depends on the linear density, breaking elongation, Poisson’s ratio of the composite rope and modulus, twist angle, friction coefficient of strings. Six island phase structure composite rope core yarn with the same radius but different sisal hemp to PET filament ratio was prepared, and the tensile strength of the composite rope core was measured. The experimental results were in good agreement with the predicted results, indicating that this model provides a convenient and valuable approach in predicting the tensile strength of composite rope core yarn based on its material composition and spinning parameters. This work not only gives the simple calculation method for estimating the breaking strength of the composite rope core, but also has important significance for the optimal design of the composite rope core yarns.

Artificial disc replacements (ADRs) are orthopaedic implants designed to replace degenerated intervertebral discs, a common aetiology of chronic back pain. ADRs which emulate the biomechanics of the natural disc promote the natural physiological kinematics, which is important for minimising postoperative deterioration of surrounding structures. By quantifying and comparing the displacements and strains within the ADR and the natural disc, target values can be established for future biomimetic ADR designs. However, measuring internal strain in these devices can be challenging. To this end, this study presents a novel application of fibre optic strain sensing through the use of fibre Bragg gratings. In this proof-of-principle study, an ADR model was fabricated with an embedded fibre optic sensor and subjected to physiological loads. The ADR model consisted of an elastomeric ring reinforced with Kevlar fibre. This simulated the annulus fibrosus (AF) of the natural disc and was left either filled or unfilled with an elastomeric material which simulated the nucleus pulposus (NP) of the natural disc. Fixation of the disc to artificial bone was achieved using three pins on the superior face and three pins on the inferior face of the ADR. Using wavelength division multiplexing of the fibre Bragg gratings, the hoop strain within the AF was monitored with a spatial resolution of 10 mm. Measurements revealed local strain concentrations around the fixation points and that the nucleated configuration increased circumferential strain in the AF by over 10 times for a given axial displacement. The measured strain asymmetry was correlated with lateral bending angle with an accuracy of ±0.5 degrees, which could be applied to tracking changes to the range of motion in load-controlled bending tests, for example. With further development, this technology has the ability to assess future designs during pre-clinical testing.

This research delved into the effects of topological modification on the nonlinear bifurcation properties of herringbone gear transmission system (HGTS). A model utilizing the potential energy method was initially developed to analyze the time-varying meshing stiffness (TVMS) of a herringbone gear following topological modification. Additionally, a dynamic model of a bending-torsion-axis-pendulum (BTAP) coupling of HGTS with 24 degrees of freedom (DOF) was established, which took into account various factors such as topological modification, meshing errors, TVMS, damping, backlash, and bearing clearance. The model employed the Runge-Kutta method to assess the pre-topological and post-topological modification nonlinear vibration responses and bifurcation characteristic, with a specific emphasis on backlash, and speed variations. The bifurcation diagram and maximum lyapunov exponent (MLE) graph were employed to elucidate these changes. Supplementary studies utilizing time domain diagram, frequency domain diagram, phase plane diagram, poincaré map analyses provided a comprehensive understanding of the HGTS’s nonlinear dynamics. The findings indicate that while the fundamental vibration and bifurcation trends persist post-topological modification, local bifurcation and vibration responses exhibit improvements. Specifically, an increase in backlash leads to a transition from single-periodic to multi-periodic, and then to chaotic regimes, the topological modification improves in reverting some chaotic behaviors to periodic, thereby reducing the extent of chaos. Increased rotational speeds result in periodic-chaotic-periodic sequences, but topological modification shifts bifurcation points, reducing chaos. Comparisons of experimental and theoretical data corroborate the model’s accuracy, demonstrating consistent trends.

In this article, a model of two dimensional problem of generalized thermoelasticity for a homogeneous isotropic nonlocal microstretch saturated porous medium with variable thermal conductivity is established. The enunciation is applied to generalized thermoelasticity theory based on Moore-Gibson-Thompson heat conduction model. The formulae for amplitude ratios and energy ratios corresponding to various reflected waves have been presented, when a set of coupled waves strikes obliquely at the boundary surface of the assumed model. The numerical values of modulus of reflection coefficients are presented graphically to depict the effects of microstretch parameter, porosity, variable thermal conductivity, and non local parameter. Expressions of energy ratios have also been obtained in explicit form and are shown graphically as functions of angle of incidence. It has been verified that during the reflection phenomenon, the sum of energy ratios is equal to unity at each angle of incidence. Results of some earlier workers have been deduced from the present formulation.

This paper presents a detailed finite element formulation to examine the static bending behavior of a four-layer beam construction. The two outermost layers consist of functionally graded materials (FGM), whilst the two interior levels are constructed of homogeneous materials. A sliding interaction transpires among all four layers when an external force is applied. Shear connections are included in the model to avert possible movement between these layers. The Timoshenko beam theory and two-node beam element are used to formulate mathematical and mechanical equations. The computational program is executed via MATLAB software. Then, verification instances are supplied to validate the precision of the deployed computational program. Parametric evaluation is performed to evaluate the influence of geometric and material properties on the static bending behavior of the beam. The results of the paper illustrate the attractive nature of the proposed model. Moreover, several interrelated concerns, including buckling analysis, dynamic analysis, and structural optimization, may be inferred from this paper.

This manuscript investigates the disruptions occurring in a two-dimensional homogeneous, isotropic, thermoelastic medium with diffusion, double porosity and microtemperatures under Lord and Shulman (LS) theory of generalized thermoelasticity. A mechanical load is applied at the outer free surface of the solid half-space. To procure the exact expressions for various field variables, normal mode analysis is utilized. Numerical computations are performed for a particular material and the acquired results are visualized through graphical representations with the aid of MATLAB software. Comparisons are carried out to elucidate the influences of diffusion parameter, time, double porosity and intensity of load on the resulting quantities. 2010 MSC: 74A15, 80A20.

This study presents a semi-analytical solution that can calculate the free vibration frequencies of functionally graded nanobeams with three distinct pore distributions under both deformable and rigid boundary conditions, based on nonlocal elasticity and Levinson beam theories. The novelty lies in the incorporation of transverse springs at both ends of porous functionally graded nanobeams and introducing a general eigenvalue problem dependent on the stiffness of these springs. This solution provides vibrational frequencies considering Levinson beam theory, non-local elasticity theory, spring stiffnesses, porosity coefficients, and temperature change. Additionally, the vibrational behavior of these porous nanobeams is explored through machine learning (ML) techniques. Four ML models namely artificial neural network (ANN), support vector regression (SVR), decision tree (DT), and extreme gradient boosting (XGB) are trained to predict the natural frequencies of nanobeams with varying pore distributions. The Sobol quasi-random space-filling method is employed to generate samples by altering input feature combinations for different porous nanobeam distributions. Model performance is evaluated using different performance indicators and visualization tools, with optimal hyperparameters determined via a Bayesian optimization algorithm. Results underscore the efficacy of ML models in predicting natural frequencies, with SVR and ANN demonstrating superior performance compared to XGB and DT. Notably, SVR and ANN exhibit exceptional R2 values of 0.999, along with the lowest MAE, MAPE, and RMSE values among the models assessed. At the end of the study, the effects of various parameters on porous gold (Au) nanobeams using the solution of the presented eigenvalue problem are discussed.

The bubble and crack defects in the production and operation of the rubber core of the rotating blowout preventer (RBOP) easily cause fatigue failure, leading to well-controlled severe accidents. Based on Yeoh’s principal structure equation, the dynamic sealing model of rubber core was established in this paper. The sealing process of the rubber core in lifting and drilling was calculated and analyzed. The stress influence law of typical cracks and bubble defects that affect the fatigue failure of rubber core sealing surface was analyzed. The results are as follows: (1) When the drill pipe joint passes through the RBOP, the structure of the rubber core is significantly deformed. This stage may cause damage and failure of the rubber core. (2) The cracks and bubble defects lead to a decrease in the stability of the sealing surface. With the increase of stress at the defect, the crack of the rubber core is easy to expand. (3) In the same location of the rubber core defects, cracks compared to bubble defects have a more significant impact. For the same type of crack, the bottom left side (A1) and the outer surface underside (D1) crack reduce the stress at the position of the rubber core sealing surface to the maximum. The research results provide a reference basis for defect detection, sealing performance, and service life of rubber cores, in order to improve the reliability evaluation standards of blowout preventer rubber cores, improve well control safety, reduce the occurrence of safety accidents, and improve operational efficiency.