Full-scale experimental crash tests are important to determine the occupant risk factors and understand barrier system behaviour in vehicle-barrier impacts. Due to the expensive and time-consuming ...nature of such crash tests, finite element simulations of full-scale crash tests to analyse and design road safety structures have gained popularity as a more practical method of assessment. In this research, a simplified simulation technique was employed by dividing the barrier system into two sections called the Impact Zone and the Rigid Zone, which was adopted for concrete crash barriers for the first time. A previously performed experimental crash test was used to successfully validate the numerical model. The numerical crash model accurately predicted the critical parameters of the barrier performance. The numerical simulation was further used to extract otherwise difficult or impossible results from the experimental crash test, such as internal energies and exit angles. The importance of the use of optimised Karagozian and Case concrete material parameters was demonstrated through a parametric study carried out with autogenerated parameters. A parametric study performed with impact speed and angle proved that increased speed is more harmful for occupants than a more oblique impact angle. The potential benefits of replacing traditional concrete with improved energy absorbing concrete to reduce occupant risks were also investigated. The comparison of results between the numerical models and experimental crash test confirms the trustworthiness of the developed models to simulate the vehicle-barrier crashes for analysing existing barrier designs and further developing new barrier designs to increase road safety.
•K&C material model calibration to represent the concrete performance.•Efficiency of modelling crash tests with calibrated material model parameters.•The effect of friction on the crash-barrier performance.•The benefits of using an energy absorbing concrete for road barriers.
Abstract This is Part II of a multipart article on a hyperelastic extended Kirchhoff–Love shell model with out-of-plane normal stress. We introduce an isogeometric discretization method for ...incompressible materials and present test computations. Accounting for the out-of-plane normal stress distribution in the out-of-plane direction affects the accuracy in calculating the deformed-configuration out-of-plane position, and consequently the nonlinear response of the shell. The return is more than what we get from accounting for the out-of-plane deformation mapping. The traction acting on the shell can be specified on the upper and lower surfaces separately. With that, the model is now free from the “midsurface’ location in terms of specifying the traction. In dealing with incompressible materials, we start with an augmented formulation that includes the pressure as a Lagrange multiplier and then eliminate it by using the geometrical representation of the incompressibility constraint. The resulting model is an extended one, in the Kirchhoff–Love category in the degree-of-freedom count, and encompassing all other extensions in the isogeometric subcategory. We include ordered details as a recipe for making the implementation practical. The implementation has two components that will not be obvious but might be critical in boundary integration. The first one is related to the edge-surface moment created by the Kirchhoff–Love assumption. The second one is related to the pressure/traction integrations over all the surfaces of the finite-thickness geometry. The test computations are for dome-shaped inflation of a flat circular shell, rolling of a rectangular plate, pinching of a cylindrical shell, and uniform hydrostatic pressurization of the pinched cylindrical shell. We compute with neo-Hookean and Mooney–Rivlin material models. To understand the effect of the terms added in the extended model, we compare with models that exclude some of those terms.
Guided ultrasonic wave based structural health monitoring has been of interest over decades. However, the influence of prestress states on the propagation of Lamb waves in thin-walled structures is ...not fully covered yet. So far experimental work presented in the literature only focuses on a few individual frequencies, which does not allow a comprehensive verification of the numerous numerical investigations. Furthermore, most work is based on the strain-energy density function by Murnaghan. To validate the common modeling approach and to investigate the suitability of other nonlinear strain-energy density functions, an extensive experimental and numerical investigation covering a large frequency range is presented here. The numerical simulation comprises the use of the Neo-Hooke as well as the Murnaghan material model. It is found that these two material models show qualitatively similar results. Furthermore, the comparison with the experimental results reveals that the Neo-Hooke material model reproduces the effect of prestress on the difference in the Lamb wave phase velocity very well in most cases. For the Formula: see text wave mode at higher frequencies, however, the sign of this difference is only correctly predicted by the Murnaghan model. In contrast to this, the Murnaghan material model fails to predict the sign change for the Formula: see text wave mode.
We derive a hyperelastic shell formulation based on the Kirchhoff–Love shell theory and isogeometric discretization, where we take into account the out-of-plane deformation mapping. Accounting for ...that mapping affects the curvature term. It also affects the accuracy in calculating the deformed-configuration out-of-plane position, and consequently the nonlinear response of the material. In fluid–structure interaction analysis, when the fluid is inside a shell structure, the shell midsurface is what it would know. We also propose, as an alternative, shifting the “midsurface” location in the shell analysis to the inner surface, which is the surface that the fluid should really see. Furthermore, in performing the integrations over the undeformed configuration, we take into account the curvature effects, and consequently integration volume does not change as we shift the “midsurface” location. We present test computations with pressurized cylindrical and spherical shells, with Neo-Hookean and Fung’s models, for the compressible- and incompressible-material cases, and for two different locations of the “midsurface.” We also present test computation with a pressurized Y-shaped tube, intended to be a simplified artery model and serving as an example of cases with somewhat more complex geometry.
•A bond-associated deformation gradient based on the deformation states within a bond's vicinity is proposed for correspondence material model.•This bond-associated deformation gradient can better ...represents the mapping between deformation states in reference and current configurations.•This bond-associated deformation gradient can be used to resolve the inherent material instability issue in standard correspondence model without introducing additional stabilizing penalty force term as is usually done in the literature.
Non-ordinary state-based peridynamic correspondence material model is known to have issues with material instability, i.e. the existence of zero-energy modes, due to non-unique mapping between deformation states and force states via the conventional peridynamic deformation gradient. In this paper, an alternative approach in which the deformation gradient hence force state are computed specifically for each individual bond is proposed to eliminate the material instability. Bond-associated deformation gradient is calculated based on deformation states within an individual bond's proximity, termed here as the bond-associated family, rather than the whole family. This bond-associated deformation gradient can better represents the force state of each individual bond from the deformation states within its proximity, and hence inherently resolves issues of material instability in the conventional correspondence material model. Parametric study on bond-associated horizon size indicates that the optimal size should be no less than the material point's horizon size but smaller than two times of that value. Comparisons against reference solutions using finite element method establish the validity and accuracy of the proposed formulation.
•High hardness perforated plates can be used effectively in ballistic protection.•Perforated plate has potential of decreasing areal mass efficiency dramatically.•The defeating mechanism of ...multilayer perforated plates includes three principles.•Deviation from trajectory, core fracture and nose erosion are defeating mechanisms.•With the simulations and tests, the bullet defeating mechanism has been explained.
In this paper, some of the important defeating mechanisms of the high hardness perforated plates against 7.62×54 armor piercing ammunition were investigated. The experimental and numerical results identified three defeating mechanisms effective on perforated armor plates which are the asymmetric forces deviates the bullet from its incident trajectory, the bullet core fracture and the bullet core nose erosion. The initial tests were performed on the monolithic armor plates of 9 and 20mm thickness to verify the fidelity of the simulation and material model parameters. The stochastic nature of the ballistic tests on perforated armor plates was analyzed based on the bullet impact zone with respect to holes. Various scenarios including without and with bullet failure models were further investigated to determine the mechanisms of the bullet failure. The agreement between numerical and experimental results had significantly increased with including the bullet failure criterion and the bullet nose erosion threshold into the simulation. As shown in results, good agreement between Ls-Dyna simulations and experimental data was achieved and the defeating mechanism of perforated plates was clearly demonstrated.
Ice, as a novel green and sustainable building material, has attracted more and more attention in building engineering. Appropriate ice material models are crucial for the performance analysis of the ...increasing ice structures. There is still challenging in modelling ice responses due to the complexity of ice. This study aims to present a nonlinear elastoplastic damage model for ice material. First, a triaxial compression test of artificial ice is conducted. Based on the test results, the modified Tsai-Wu failure criterion with better performance in the tensile zone and physical meaning for hydraulic strength is established. Then, combining plasticity theory with damage mechanics, an elastoplastic damage constitutive law considering the difference between tensile and compressive properties is proposed. The piecewise damage model and the Weibull exponential damage model are employed for compression and tension damage, respectively. Moreover, the numerical iterative algorithm is developed and a user-defined material subroutine (UMAT) is embedded in the finite element software ABAQUS to simulate the mechanical properties of ice. Furthermore, the constitutive model is verified by comparing the FEM results with the results of uniaxial compression, triaxial compression, and three-point bending tests. The results show that the constitutive model can well describe the stress-strain nonlinear behavior and capture the basic failure mode of ice materials. Finally, considering temperature affecting on the failure surface, a temperature dependent ice material model is developed. The current study would help in the design, operation and maintenance of ice structures.
•A modified Tsai-Wu failure criterion is provided and compared by triaxial tests.•The yield surface evolution and damage evolution are considered.•A fiber damage model based on Weibull theory is proposed for ice under tension.•Theory and implementation of the elastoplastic damage model for ice are presented.•Temperature-dependent elastoplastic damage constitutive model is developed.
Abstract Underground coal seam mining significantly alters the stress and energy distribution within the overlying rock, leading to eventual structural degradation. Therefore, it is imperative to ...quantitatively identify the temporal and spatial characteristics of stress evolution of overlying rock caused by mining. This paper introduces a novel rock stress model integrating entropy and a spatial–temporal cube. Similar material model tests are used to identify the abrupt entropy changes within the mining rock, and the trend analysis is carried out to describe the spatial–temporal evolution law of stress during mining. Experimental findings indicate elevated stress levels in the unmined rock preceding and following the panel, as well as within specific rock strata above it. Definitively, dynamic stress arches within the surrounding rock of the stope predominantly bear and distribute the load and pressure from the overlying rock, and each stress mutation is accompanied by a sudden stress entropy change. Over time, z-score shows that the noticeable reduction in mining-induced overburden stress becomes increasingly pronounced, especially in the water-conducting fracture zone. The model's bifurcation set serves as the comprehensive criterion for the entropy-induced sudden changes in the rock system, signifying overall failure.
•An orthogonal cutting-based method was modified to obtain J–C model parameters.•J–C material model of stainless steel 17-4PH was newly obtained and verified.•Curvilinear micro-grooved tools were ...newly designed and tested by 3D FEM.•New designed tools can reduce friction, cutting forces and temperature notably.•New designed tools can weaken stress concentration on cutting edges.
Micro-texturing techniques are applied to improve the performance of cutting tools by improving the tribological performance. However, sharp edges of linear micro-grooved tool designs may adversely affect tool-chip contact, create interlocking effects, and weaken the potential benefits. This paper investigates new designs in curvilinear micro-grooves on the cutting tool rake face to reduce the interlocking effect and further improve the performance. A modified methodology that uses an orthogonal cutting model and inverse analysis was utilized to determine the Johnson–Cook (J–C) constitutive material model parameters for stainless steel 17-4PH. The finite element method (FEM) simulation results in force predictions confirmed that this methodology is suitable to obtain J–C model parameters used in high-speed machining regimes. Then, three-dimensional (3D) simulations for rough and finish turning were developed and validated for machining with the non-textured cutting tool. The performance of cutting with curvilinear micro-grooved tools was investigated by 3D FEM simulations. These newly designed micro-grooved tools showed improved performance in tool-chip friction, chip formation, cutting force, temperature, and tool stress fields than non-textured and linear micro-grooved designs.
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This is the first part of a two-part article on a hyperelastic extended Kirchhoff–Love shell model with out-of-plane normal stress. We present the derivation of the new model, with focus on the ...mechanics of the out-of-plane deformation. Accounting for the out-of-plane normal stress distribution in the out-of-plane direction affects the accuracy in calculating the deformed-configuration out-of-plane position, and consequently the nonlinear response of the shell. The improvement is beyond what we get from accounting for the out-of-plane deformation mapping. By accounting for the out-of-plane normal stress, the traction acting on the shell can be specified on the upper and lower surfaces separately. With that, the new model is free from the “midsurface” location in terms of specifying the traction. We also present derivations related to the variation of the kinetic energy and the form of specifying the traction and moment acting on the upper and lower surfaces and along the edges. We present test computations for unidirectional plate bending, plate saddle deformation, and pressurized cylindrical and spherical shells. We use the neo-Hookean and Fung’s material models, for the compressible- and incompressible-material cases, and with the out-of-plane normal stress and without, which is the plane-stress case.
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