Bending test and numerical analysis of inflatable tubes

Large-scale advanced high strength steel (AHSS) sheet specimens were deformed in uniaxial tension, using a novel grip system mounted on a MTS universal tension machine. After pre-strain, they were used as a pre-strained material to examine the anisotropic response in the biaxial tension tests with various load ratios, and orthogonal tension tests at 45° and 90° from the pre-strain axis. The flow curve and the instantaneous r-value of the pre-strained steel in each of the aforementioned uniaxial testing conditions were also measured and compared with those of the undeformed steel. Furthermore, an exhaustive analysis of the yield surface was also conducted and the results, prior and post-prestrain were represented and compared. The homogeneous anisotropic hardening (HAH) model [1] was employed to predict the behavior of the pre-strained material. It was found that the HAH-predicted flow curves after non-linear strain path change and the yield loci after uniaxial pre-strain were in good agreement with the experiments, while the r-value evolution after strain path change was qualitatively well predicted.

Hyperelastic material simulation is necessary for proper testing of products functionality in cases where prototype testing is expensive or not possible. Hyperelastic material is nonlinear and more than one stress-strain response of the material is required for its characterization. The study was focused on prediction of hyperelastic behavior of rubber neglecting the viscoelastic and creep effects in rubber. To obtain the stress strain response of rubber, uniaxial and biaxial tension tests were performed. The data obtained from these tests was utilized to find the coefficients of Mooney-Rivlin, Odgen and Arruda Boyce models. Verification of the behavior as predicted by the fitted models was carried out by comparing the experimental data of a planar shear test with its simulation using the same constitutive models.

An effective biaxial tension and compression test method is proposed based on the shortcomings of current research for the mechanical properties of solid propellants under complex stress states. The equal proportion biaxial tension and compression test of HTPB (Hydroxyl-terminated polybutadiene) and NEPE (NitrateEster Plasticized Polyether) solid propellants is performed at different rates while at room temperature, and the damage morphology of the tension–compression zone is analyzed using micro-CT. The results show that the failure mode of the solid propellant under biaxial tension and compression loading is similar to that under uniaxial tension. Meanwhile, the compressive strength is much greater than the tensile strength, which will eventually cause tensile failure. With an increased loading rate, the growth trend of the initial modulus, ultimate strength, and maximum elongation of the propellant is gradually flattened, and the damage degree is gradually reduced. Additionally, damage that forms in the HTPB propellant is from dewetting and particle fracture while that for the NEPE propellant is from matrix tearing. The porosity can be used as the meso-damage parameter of the propellant.

In this study, experimental and numerical analyses of Forming Limit Diagram (FLD) for Advanced High Strength (AHS) steel grade 980 were performed. Forming limit curve was first determined by means of the Nakazima stretch-forming test. Then, analytical calculations of the FLD based on the Marciniak-Kuczynski (M-K) model were carried out. Different yield criteria, namely, Hill’48 (r-value and stress-based), Yld89 (r-value and stress-based) and Barlat2000 (Yld2000-2d) were investigated. The strain hardening law according to Swift was applied. To identify parameters of each model, uniaxial tension, balanced bi-axial bulge test and in-plane biaxial tension test were performed. As a result, predicted plastic flow stresses and plastic anisotropies of the AHS steel by various directions were evaluated. In addition, effects of the anisotropic yield functions, strain rate sensitivities, imperfection values and work hardening coefficient on the predicted FLD were studied and discussed. It was found that the FLD based on the Yld2000-2d yield criterion was in better agreement with the experimental curve. Accuracy of the FLD predictions based on the M-K theory, especially in the biaxial state of stress, significantly depended on the applied yield criteria, for which yield stresses and r-values of different loading directions were required.

We show a general nonlinear stress-strain response for crystalline materials subject to an initial deformation. The scheme is implemented using 3rd, 4th, and higher order elastic constants. We apply the formulation to a face-centered cubic crystalline Au under shear while in an initially hydrostatically deformed state. We then compare the nonlinear shear stress-strain relations from our derived formulation with Hellmann-Feynman shear stress-strain curves obtained directly from ab initio calculations. The results show that the general analytical expression for the nonlinear stress-strain relation is satisfactory and thus expected to have many applications where ab initio calculations are limited, including cases at finite temperature.

Testing, characterization and numerical prediction (uni-axial tension and bend test) of Double-side TIG welded SS321 plate for pressure vessel application

The body wall structure of Clanis bilineata larva exhibits strong stability. This characteristic prompted the development of a new inflatable tube to improve the stability under axial pressure. The C. bilineata larva was chosen to observe the connection between its body wall and nearby muscle tissues, as well as the distribution of these tissues, by using the tissue section technique. Using this method, an inflatable tube with reinforcing ribs was designed. Simulation using the finite element method and experimentation were employed to compare and analyze the stability of the inflatable tube with and without reinforcing ribs under different axial pressure levels. Results indicate that the ultimate load of both inflatable tubes increases linearly with increasing pressure. The difference between the slopes of the two lines is small. Under different axial pressure levels, the ultimate load of the inflatable tube with reinforcing ribs is about 1.34[Formula: see text]N higher than that without reinforcing ribs; the ultimate compression power increased by 31% to 68% compared with that without ribs. The simulation results are slightly larger than the experimental results, but the ultimate load value in the simulation exhibits the same trend as that in the experiment. Finally, the limit load and ultimate compression power are used as evaluation criteria to quantitatively analyze the stability performance of an inflatable tube with reinforcing ribs under axial pressure.

A peristaltically actuated device, PADeMIS, composed of silicone rubber (SR) is under development for use in minimally invasive surgery. During locomotion, the device will be subject to a few thousand load changes involving varying, sometimes high, strains. The design is being optimised by finite element analysis, for which a constitutive law for the mechanical behaviour of silicone rubber is required. Uniaxial and biaxial tension tests have been performed on specimens of used silicon rubber. Synchronous fitting of uniaxial and biaxial tensile data gives significantly better results than using uniaxial or biaxial results alone to derive constitutive laws. The mechanical properties of SR were found to change from loading to loading up to few thousand cycles. Hence, simulating the deformation of SR structures is problematic. Furthermore, variability was observed between batches of SR.

Uniaxial and biaxial mechanical tester was developed tp perform basic test for characterization of soft, low strength polymer gels. We have considered stress/strain relationship of acrylamide-based and polyacrylonitrile (PAN) fiber and sheet gels. Acrylamide-based gels were tested uniaxially, where Young's modulus estimated varies between 10 and 25 kPa. Uniaxial and biaxial tension test were performed on PAN sheets, from which Young's modulus was estimated at 6.65 Mpa, which is an extraordinarily large strength than the conventionally investigated acrylamide- based gels. Its length change in response to EtOH/H<SUB>2</SUB>O solution exchange proved to be not small as an actuator material, and it was observed that PAN exhibited a deformation in response to the electric field. Two types of PAN gel fibers were tested as a bundle of 50 fibers. True stress-strain data were obtained showing similar non-linear trend in both case. Statistical methods were used to assess fiber strength distribution.

On the appearance of fractional operators in non-linear stress–strain relation of metals

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;Accurate prediction of the ultimate breakage pressure load for pyro-inflator housing is a critical aspect of inflator development. In this study, the tensile test of a specimen, from its initial shape to fracture, is simulated to verify the material properties of the inflator housing. The numerical results demonstrate high accuracy, with the tensile force–displacement curve, maximum tensile force, necking in the concentrated instability zone, fracture location, and inclined angle all closely matching the experimental data. Following material correlation, the ultimate breakage load of the inflator housing under hydrostatic burst test conditions is calculated using an explicit solver. A stress tensor state analysis method is proposed to define the ultimate load based on the onset of plastic instability in the thickness direction at the top center of the inflator. Compared to experimental results, the accuracy of the ultimate breakage pressure prediction using this method is 99.04%, while the accuracy using the arc-length implicit algorithm is 97.10%. By analyzing the stress and strain changes in key positions during uniaxial tensile and hydrostatic burst biaxial tensile tests, this method provides high precision in forecasting ultimate loads and defining fracture strains. Future work will investigate dynamic loading effects and machine learning–enhanced instability criteria, with particular attention to the influence of manufacturing stamping processes on predictive model accuracy.&lt;/div&gt;&lt;/div&gt;

Textiles are widely used in tensile structures due to their low weight, flexibility, and ability to span large areas efficiently through membrane action. Weft-knitted textiles, in particular, offer customization at a unit level, enabling the creation of locally programmable, 3D-shaped, continuous membranes. However, their mechanical characterization remains challenging, despite its importance for structural applications such as flexible formwork. This study examines the biaxial elastic properties of CNC weft-knitted textiles, focusing on the influence of knit architecture on their mechanical response. A custom biaxial tensile testing setup was developed to test three knitting patterns – interlock, tuck, and hexagonal – under three strain ratios (1:2, 1:1, and 2:1). Results show that stiffness varies significantly with knitting pattern and direction, reflecting asymmetries in textile microstructure. Strain distribution was also found to be non-uniform, with lower strains at the core than on the edges, highlighting the role of boundary conditions. Beyond providing insights into weft-knitted textile behaviour, this study contributes to an experimental framework for biaxial stiffness evaluation. The methodology serves as a proof-of-concept framework for the biaxial testing, test preparation, and result interpretation for knitted textiles, as well as for developing low-cost biaxial testing setups. These findings are particularly relevant for architectural and construction applications, where understanding the mechanical behaviour of knitted textiles is essential for structural integrity and design optimization. • The biaxial tensile behaviour of CNC knitted textiles is experimentally evaluated. • A low-cost custom biaxial tensile testing setup for knitted textiles is developed. • Apparent tangent and elastic moduli describe stiffness in two deformation phases. • Knitting pattern and strain ratio strongly influence the textile biaxial stiffness. • The strain distribution is non-uniform, with lower strains recorded at the core.

Lack of energy dissipation is one of the shortcomings of conventional glass fiber reinforced composites. The addition of steel fibers to the conventional FRP composite to create a hybrid composite has been recently investigated as an option to address this limitation. The current literature is limited to composites reinforced with metal and non-metal fibers of the same alignment. In this study, hybrid and nonhybrid FRP composites of different layups, fiber content, and weave type were manufactured and subjected to hysteretic tensile loads. Woven glass fabrics in ±45° orientation were hybridized with unidirectional stainless steel fabrics in 0° and 90° orientations. This put the glass and steel layers in in-plane shear and normal stresses, respectively. The nonlinear stress–strain relationship, residual plastic strains, energy dissipation capability, and failure mechanisms of hybrid and nonhybrid composite type were compared. The hybrid composites presented improved energy dissipation, tensile strength, and stiffness when compared to nonhybrid ones. The applicability of an existing constitutive model that was originally developed for in-plane shear of conventional composites was investigated and refinements were proposed to present the hysteretic stress–strain relationship after addition of steel fibers. The refined model captured the increased plastic strain values and energy dissipation because of stainless steel fibers in the hybrid composite samples. An Armstrong–Frederick plasticity model was implemented to model the stress–strain relationship of the stainless steel composite samples.

The integration of multi-sensor imaging and deep learning techniques has emerged as a pivotal innovation in advancing structural mechanics, particularly in the prediction of stress and strain distributions. This study falls within the thematic scope of multi-sensor imaging and fusion methods, emphasizing their crucial role in assessing material behavior under complex conditions. Traditional methodologies, such as finite element methods and classical constitutive models, often fall short in capturing the intricacies of heterogeneous materials and nonlinear stress–strain relationships. These limitations necessitate a more robust computational framework capable of addressing material variability and computational efficiency challenges. To this end, we propose the Stress–Strain Adaptive Predictive Model (SSAPM), which synergizes mechanistic modeling with data-driven corrections. Leveraging hybrid representations, adaptive optimization strategies, and modular architectures, SSAPM ensures precision by embedding physics-informed constraints and reduced-order modeling for computational scalability. Experimental validations underscore the model’s capability to generalize across diverse structural scenarios, outperforming conventional approaches in accuracy and efficiency. This work establishes a transformative pathway for incorporating multi-sensor data fusion into structural analysis, advancing the predictive power and applicability of stress–strain models.

Nonlinear stress-strain relationships in tissue and their effect on the contrast-to-noise ratio in elastograms