International Journal of Mechanics and Materials in Design最新文献

The tube hydroforging process (THFG) is an advanced technology for manufacturing tubular components with complex cross-sections. The positive-curvature arc is one of the most fundamental and difficult-to-form features of complex cross-sections. However, its wrinkling mechanism in the THFG process cannot be explained by the existing theory. This restricts the application of the technology. First, because of the bending deformation caused by the excessive circumferential force, compression instability occurs at the positive-curvature arc part. This results in wrinkling similar to that in the conventional linear part. In addition, owing to the existence of the positive-curvature arc, the circumferential force produces a component force along the vertical direction that causes rigid displacement of the materials. This yields another new instability model: motion instability. The corresponding critical pressures for the two instability models were determined by adopting static method and energy methods respectively. Theoretically, motion instability is dominant in the early stages of compression, whereas compression instability is dominant in the subsequent stages. However, considering actual production, the correlations between the critical pressures of the different parts were compared. The wrinkling of the linear part inhibits the occurrence of compression instability in the positive-curvature arc. Thus, wrinkling of the arc can be caused only by motion instability. Therefore, the critical pressure for motion instability is defined as the critical pressure required for the positive-curvature arc. In addition, a forming window that considers the critical pressure of each part was established successfully.

Traditional acoustic materials typically have fixed acoustic bandgaps (BGs), making them unsuitable for complex vibration environments. In recent years, prestress-controlled acoustic metamaterials have emerged as an effective solution. However, most existing studies fail to meet the requirements for achieving broadband acoustic control in the low-frequency range (below 600 Hz). Therefore, this study introduced a negative Poisson’s ratio structure, utilizing the so-called “trampoline effect,” building on previous research to design a low-frequency, broadband negative Poisson’s ratio structure acoustic metamaterial (NPRS-SC). It utilizes compression, rather than tension, conditions to control BGs. Numerical results indicate that the first low-frequency BG of NPRS-SC ranges from 66.1 to 281.1 Hz, with a lower starting frequency and broader stopband compared to traditional structures. It also demonstrates superior vibration damping performance. Importantly, by introducing compressive prestress conditions, the BG range can be gradually expanded, enhancing vibration damping performance. Specifically, when the strain value λ is set to − 0.03, NPRS-SC’s first low-frequency BG can cover 85% of the frequency range below 600 Hz. Lastly, this study analyzes the influence of NPRS-SC’s geometric parameters on its first low-frequency BG and vibration transmission performance. This research provides essential references and guidance for designing tunable, low-frequency, broadband acoustic metamaterials, offering robust support for future developments in acoustic control technology.

A novel material testing concept is developed in order to provide tensile and compressive properties within a single mechanical test. A new specimen geometry is designed for testing in a universal testing machine. Under tensile load, both a homogeneous tensile stress condition as well as a homogeneous compressive stress condition occur in the specimen. Measurements accompanying the experimental test with digital image correlation provide tensile and compressive Poisson’s ratio as well as tensile modulus. These properties are input parameters for subsequent finite element simulations. The compressive modulus is determined by iteratively adjusting finite element simulations in order to couple experimental and simulated results. For validating the concept, experimental tests are carried out on polyoxymethylene. While the tensile Poisson’s ratio of the new concept shows the best agreement with the reference value, the compressive modulus is approximately 15% higher. Further work should focus on an appropriate material model in order to reduce the deviation.

In recent years, significant attention has been garnered by Tailor Rolled Blanks (TRBs), especially within the automotive industry, attributed to their unique performance characteristics, defined by varying thickness profiles. Nonetheless, the inherent structural complexities of TRBs have led to non-uniform deformation during forming processes, thereby compromising elongation and formability. In this study, an exploration into the deformation of TRBs under uniaxial tensile conditions is elucidated, centering specifically on TRBs transitioning from a thickness of 1–2 mm over a 100 mm span. An assessment of the properties of TRBs following partial annealing is conducted, and mechanisms responsible for thickness variations and the revelation of intrinsic mechanical traits are identified through microstructural examinations. Exploration of the mechanical behavior of TRBs under tension is undertaken, and a methodological approach for optimizing the distribution of mechanical properties is proposed. Validation is achieved through the employment of finite element models, showcasing a performance improvement in the optimized TRBs, with uniform elongation rates surpassing those of non-optimized TRBs by up to 197%. Moreover, an outperformance of uniform-thickness materials by up to 51% is exhibited by the optimized TRBs. These insights are anticipated to bolster the application and efficiency of TRBs across various engineering sectors, aligning coherently with the intelligent design and advanced materials implications within the realm of mechanics and materials in design, as spotlighted by "The International Journal of Mechanics and Materials in Design". This exploration intricately intertwines mechanics, material engineering, and intelligent design, offering a comprehensive view that stands to fortify the symbiotic relationship between advanced materials and the design process.

The immersed roller is very common in the roll-to-roll industry, such as hot dip galvanizing, electroplating, roll coating. In these applications, the strip is developing thinner and wider, and its flexibility is also strengthening. The vibration of the sinking roller has an increasingly significant impact on its product quality. A theoretical model was established to study the sink roller immersed in fluids, and modal tests and corresponding finite element simulations were carried out to study the sink roller's characteristics. The effects of roller density, wall thickness, fluid density, viscosity, and constraint conditions on modal characteristics were investigated. The results were well-validated, and the modal tests in air with and without a rod have high consistency, proving the reliability. The first six peak values of FRF curves are clear when immersed in water and hydraulic oil, but only the first three are evident in glycerin. It is observed that the viscosity of glycerin has a minor effect on natural frequencies, but the added damping factor grows when viscosity increases. The added mass factor rises linearly with the growth of wall thickness or liquid density while decreasing when the structure's density increases. The added mass factors of the (1,2)th and (2,2)th modes are more significant than the bending modes. A rigid-body displacement occurs at the constrained end journal of bending mode for rollers in liquids. Liquid density is the main factor affecting natural frequencies, especially for aluminum rollers. The maximum frequency growth rates under the constrained state of the steel and aluminum rollers in water are 5.7% and 20.4%, respectively, on the (2,2)th mode. Moreover, it increases with the increase of liquid density and viscosity, which leads to higher resonance probability. It can provide a basis for the dynamics research of similar systems.

This paper investigates stability and free vibration behaviours of bi-directional functionally graded material (BDFGM) curved sandwich beams. Simultaneous variation of material compositions along tangential and radial direction is considered. A three-node curved isoparametric beam element based on a 4-parameter global–local shear deformation theory is employed. The obtained results are verified with those from literature. Various parameters such as aspect ratio, deepness ratio, gradient indexes, boundary conditions are taken into account. Several results of BDFG curved beams are provided for benchmark purpose.

This research extensively used different progressive machine learning (ML) techniques to predict the compressive strength (CS) and tensile strain (TSt) of engineered cementitious composites (ECC) with 14 input variables and six algorithms. Specifically, random forest (RF), support vector machine, extreme gradient boosting (XGBoost), light gradient boosting machine, categorical gradient boosting (CatBoost), and natural gradient boosting techniques were used in the present study, to understand mechanical properties of ECC meanwhile these properties are crucial for design codes and developing new reliable models for mixtures. The discrepancy between the ML technique and specific ECC expected outputs is novel in this study and will aid researchers in better understanding of ECC features. To estimate the CS and TSt of the ECC, 2535 and 1469 input data points, respectively, were incorporated based on the material ratio, W/B, and different properties of the fibers. In addition, hyperparameter optimization techniques have also been used in ML to improve over fitting and make the model more accurate and robust. Moreover, an error analysis was highlighted between the actual and predicted CS and TSt of the ECC with each ML technique. Also, the significance and influence of the variable inputs that affect the CS and TSt were explained using the Shapley additive explanation (SHAP) approach. Among all approaches, CatBoost and XGBoost predicted the CS and TSt of ECC with greater accuracy than other techniques in terms of the coefficient of determination (R²), mean square error, mean absolute error, root mean square error, and symmetric mean absolute percentage error. The training and testing R² values of CatBoost and XGBoost for predicting the CS and TSt of ECC were 0.96, 0.89, 0.89, and 0.76, respectively. SHAP analysis revealed that W/B and fiber elongation were the most significant input variables for the CS and TSt of the ECC.

Graphical Abstract

An approach to estimating the dynamic characteristic of one-dimensional orthorhombic quasicrystal sector plates with various boundary conditions is presented. These investigated structures have an arbitrary angle span, and the constituent materials of these models possess a certain porosity distribution. The Green–Naghdi generalized thermoelastic equations have been applied to the sector plates in a thermal environment to obtain an explicit expression, from which the heat fluxes equation can be converted into a state equation. The state-space method is conducted in basic equations of phason and phonon fields to capture governing equations of the structures along the r-direction. Fourier series expansions are utilized to control the span of the sector plates, subject to simply supported boundary conditions along the circumferential direction. Meanwhile, the remaining boundary conditions are treated by differential quadrature technique. The global propagator matrix is proposed to overcome the numerical instabilities caused by high-order frequency and large discrete points. Numerical examples show that each order frequency follows an increasing pattern from small to large with the increase of fixed boundary conditions. The changes in angular span can cause variations in stiffness, leading to alterations in structural stability.

In view of the fact that composite material structures will be affected by multi-source uncertainty factors during use, a new method for predicting the uncertainty of the residual strength of porous laminates in hot and humid environments is proposed based on the PCE method. The influence of different hot and humid environments on the uncertainty of residual strength of porous composite laminates was studied through experimental and numerical methods. The elastic mechanical parameters of composite materials are used as random variables, and the expression of a generalized polynomial chaos expansion model for porous laminates in hot and humid environments is derived; The Hermite polynomial is introduced and the pseudo spectral projection method is used to solve the polynomial coefficients. The probability density and moment function of composite laminates under temperature and humidity changes are calculated. The results show that the output results based on polynomial chaos expansion method are generally consistent with the experimental values, and it can effectively and accurately predict the dispersion of residual strength of composite plates with holes under actual working conditions; Comparing the output results of the polynomial chaos expansion method with the Monte Carlo method, the deviations of the average and standard deviation of the two methods are controlled within 1 and 2.1%, respectively. However the calculation time of the PCE method is only 6% of that of the Monte Carlo method. The proposed polynomial chaos algorithm has the advantages of high efficiency and fast calculation speed in solving the uncertain response problem of composite materials.