A boiling liquid expanding vapor explosion (BLEVE) is one of the most serious accidents which generates overpressure and ejected fragments with potential great impact on the safety of the tank area. ...Hence, it is important to reveal the dynamic characteristics of the axial crack propagation at the top of the horizontal tank in a BLEVE accident. The rupture behavior of tanks under one-step BLEVE accidents is investigated and the detailed dynamic characteristics of crack opening angle and crack propagation rate were assessed through the small-scale BLEVE experiments with variations in tank wall thickness and filling levels. An extended Gurson-Tvergaard-Needleman (GTN) model was proposed to calculate the dynamic damage of the tank during the rupture process. The dynamic stress-strain damage characteristics of the tank during the one-step BLEVE process and the circumferential transformation mechanism of the axial crack were explored. Based on an analysis of the material damage and the size characteristics of the tank structure, criteria were proposed for judging whether the direction of crack growth will change.
A procedure for characterizing the deformation process of regular cellular structures fabricated with Fused Deposition Modelling of ABSplus material is presented. Two different topologies with ...similar relative densities were experimentally compressed for five different deformation velocities: quasi static (1.0; 5.0 and 10.0 mm/s) and dynamic (1520.0 mm/s and 2400.0 mm/s). In addition, both topologies were compared in the case of energy absorption capabilities. Firstly, however, the mechanical properties of the 3D printed material samples were evaluated and numerically correlated with the experimental data different strain rates. For this purpose, an elasto-visco-plastic constitutive model was selected and the Cowper-Symonds hardening parameters were determined using the MATLAB authorial script, which finally resulted in a good agreement between the experimental and numerical outcomes for all the considered loading conditions.
•Two different cellular structures are manufactured with FDM from ABSplus.•Quasi-static and dynamic mechanical properties of the printed ABSplus material are determined.•Cowper-Symonds hardening parameters are determined using Matlab authorial script.•Quasi-static and dynamic crashworthiness properties of the structures are assessed during FEA and experimental testing.
This paper develops and benchmarks an immersed peridynamics method to simulate the deformation, damage, and failure of hyperelastic materials within a fluid-structure interaction framework. The ...immersed peridynamics method describes an incompressible structure immersed in a viscous incompressible fluid. It expresses the momentum equation and incompressibility constraint in Eulerian form, and it describes the structural motion and resultant forces in Lagrangian form. Coupling between Eulerian and Lagrangian variables is achieved by integral transforms with Dirac delta function kernels, as in standard immersed boundary methods. The major difference between our approach and conventional immersed boundary methods is that we use peridynamics, instead of classical continuum mechanics, to determine the structural forces. We focus on non-ordinary state-based peridynamic material descriptions that allow us to use a constitutive correspondence framework that can leverage well-characterized nonlinear constitutive models of soft materials. The convergence and accuracy of our approach are compared to both conventional and immersed finite element methods using widely used benchmark problems of nonlinear incompressible elasticity. We demonstrate that the immersed peridynamics method yields comparable accuracy with similar numbers of structural degrees of freedom for several choices of the size of the peridynamic horizon. We also demonstrate that the method can generate grid-converged simulations of fluid-driven material damage growth, crack formation and propagation, and rupture under large deformations.
In current investigation, a sequential multiscale modelling strategy together with corresponding experimental validation aimed to evaluate the influence of off-axial orientation on three-dimensional ...orthogonal woven carbon/carbon composites (3DOWCCCs) pin-bearing failure behavior. A hierarchical numerical simulation methodology at micro−/meso−/macroscales was developed to obtain the predictions. With the intention of acquiring precise mechanical responses of unnotched 3DOWCCCs, fiber and void stochastic arrangements in micro-level representative volume elements (RVEs) were generated using Random Sequential Adsorption (RSA) algorithm, meanwhile the geometrical reconstruction of meso-level RVE was accomplished via X-ray computed tomography (X-CT). Moreover, off-axial angle sensitivity analysis was presented through the comparison between macroscale modelling and testing results. The stress interaction and coupling impacts were embedded in material constitutive laws, which combined Murakami-Ohno theory for yarn based on continuum damage mechanics, and exponential damage rule for carbon matrix, incorporating trilinear cohesive zone model (CZM) for interface, and the achieved predictions agreed reasonably well with the experimental results. It is concluded that, for on-axial specimen, the warp yarns fracture and material out-of-plane swelling were the primary damage mechanism, while the material out-of-plane swelling in conjunction with yarns in-plane rotation dominated the structural failure under off-axial cases.
Dust velocity in fusion devices covers a wide range (several hundreds of m/s to over 10 km/s), which can cause various interactions between energetic dust grains and wall materials. Dust grain with ...low energy can influence the wall properties by deposition. Intense dust-wall interactions can cause serious wall damage such as sputtering, degradation, deformation and so on. As beryllium and tungsten are the material of the first wall and divertor, respectively, systematically molecular dynamics simulations have been performed to study the interactions between beryllium/tungsten dust and the beryllium/tungsten wall in the present study. A wide range of dust velocity has been considered to cover the velocity from experiments. Our result shows that the influences of dust on the wall are greatly affected by the impact velocity of dust grains and the properties of the wall material. A detailed analysis shows that the dust-wall interaction can be divided into four levels and an analytical model has been developed to explain the mechanism. Character velocities that separate the interaction levels are also provided by the model. The comparison between the MD result and the model shows a good agreement. Our result is helpful for the understanding of the mechanisms and the prediction of dust-wall interactions.
Among ceramic matrix composites (CMCs), carbon fiber-reinforced silicon carbide matrix (C/SiC) composites are widely used in numerous high-temperature structural applications because of their ...superior properties. The fiber–matrix (FM) interface is a decisive constituent to ensure material integrity and efficient crack deflection. Therefore, there is a critical need to study the mechanical properties of the FM interface in applications of C/SiC composites. In this study, tensile tests were conducted to evaluate the interfacial debonding stress on unidirectional C/SiC composites with fibers oriented perpendicularly to the loading direction in order to perfectly open the interfaces. The characteristics of the material damage behaviors in the tensile tests were successfully detected and distinguished using the acoustic emission (AE) technique. The relationships between the damage behaviors and features of AE signals were investigated. The results showed that there were obviously three damage stages, including the initiation and growth of cracks, FM interfacial debonding, and large-scale development and bridging of cracks, which finally resulted in material failure in the transverse tensile tests of unidirectional C/SiC composites. The frequency components distributed around 92.5 kHz were dominated by matrix damage and failure, and the high-frequency components distributed around 175.5 kHz were dominated by FM interfacial debonding. Based on the stress and strain versus time curves, the average interfacial debonding stress of the unidirectional C/SiC composites was approximately 1.91 MPa. Furthermore, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDXS) were used to observe the morphologies and analyze the chemical compositions of the fractured surfaces. The results confirmed that the fiber was completely debonded from a matrix on the fractured surface. The damage behaviors of the C/SiC composites were mainly the syntheses of matrix cracking, fiber breakage, and FM interfacial debonding.
Understanding crack propagation in structures subjected to fluid loads is crucial in various engineering applications, ranging from underwater pipelines to aircraft components. In this work, a ...computational framework is proposed to investigate the dynamic response of structures, including their damage and fracture behaviour under hydrodynamic load. The proposed framework employs weakly compressible smoothed particle hydrodynamics (SPH) to model the fluid flow and a pseudo-spring-based SPH solver for modelling the structural response. The δ-SPH technique is implemented to enhance pressure calculations within the fluid phase. The pseudo-spring analogy is employed for modelling damage, where particle interactions are confined to their immediate neighbours. These particles are linked by springs, which do not contribute to system stiffness but determine the interaction strength between connected pairs. It is assumed that a crack propagates through a spring connecting a particle pair when the damage indicator of that spring exceeds a predefined threshold. The proposed framework is extensively validated through existing experimental and numerical data from the literature. The ability of the framework to accurately depict large material deformation, damage and fracture behaviour under hydrodynamic loads is showcased through a few numerical simulations.
•Coupled SPH framework is proposed to simulate structural failure in FSI problems.•The fluid phase is modelled by WCSPH with δ− SPH correction.•The fracture in deformable solids is modelled by pseudo-spring augmented SPH.•Results align well with benchmark tests, capturing failures in deformable solids.
•Gradient of magnetic memory signal can reflect stress concentration around crack.•Gradient of magnetic memory signal shows a linear relationship with crack size.•Crack propagation can be monitored ...and evaluated by metal magnetic memory testing.•The material damage model represented with magnetic memory characteristic is created.•Fatigue life can be predicted by relationship of damage parameter and normalized life.
To monitor the crack propagation and predict the fatigue life of ferromagnetic material, the metal magnetic memory (MMM) testing was carried out to the single edge notched specimen made from structural alloy steel under three-point bending fatigue experiment in this paper. The variation of magnetic memory signal Hp(y) in process of fatigue crack propagation was investigated. The gradient K of Hp(y) was investigated and compared with the stress of specimen obtained by finite element analysis. It indicated that the gradient K can qualitatively reflect the distribution and variation of stress. The maximum gradient Kmax and crack size showed a good linear relationship, which indicated that the crack propagation can be estimated by MMM testing. Furthermore, the damage model represented by magnetic memory characteristic was created and a fatigue life prediction method was developed. The fatigue life can be evaluated by the relationship between damage parameter and normalized life. The method was also verified by another specimen. Because of MMM testing, it provided a new approach for predicting fatigue life.
The objective of this research was to evaluate Ag+ toxicity in Trifolium pratense L. seedlings subjected to increasing doses of Ag+ by determining photosynthetic pigment and malondialdehyde (MDA) ...contents, microstructure and hereditary substance alterations, changes in activities of antioxidase-superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) as well as the content of total Ag absorbed in vivo with evaluation of root growth. Doses of approximately 80 mg L−1 Ag+ severely affected photosynthetic efficiency in Trifolium pratense L. seedlings promoted by damages in photosynthetic apparatus evidenced by downward trend in photosynthetic pigment contents and obvious chlorosis. Alterations in enzymatic activity, lipid peroxidation, genic material damage and the presence of Ag+in vivo had impacted on photosynthetic machinery as well. A hormesis effect was observed at 60 mg L−1 Ag+ for the photosynthetic pigments and antioxidase for Trifolium pratense L. seedlings. Tissue changes (i.e., roots, stems and leaves) observed in fluorescence microscope with obvious chlorosis, roots blackening and formation of agglomerated black particles, were related to the lesion promoted by excessive ROS in vivo. Asynchronous change of antioxidase activity corresponded to the alteration in the MDA content, indicating the synchronization in the elimination of ROS. The changes occurred in RAPD profiles of treated samples following Ag+ toxicity containing loss of normal bands, appearance of new bands and variation in band intensity compared to the normal plants with a dose-dependent effect. On average, the roots of Trifolium pratense L. immobilized 92.20% of the total Ag absorbed as a metal exclusion response. Root growth was significantly sensitive to Ag+ stress with obvious hormesis, which corresponded to the changes in Ag uptake, demonstrating the functional alterations in plants. To sum up, we suggest that modulating the genotype of Trifolium pratense L. seedlings to bear higher proportion of pollutants is conducive to contamination site treatment.
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•Antioxidase and photosynthetic pigments showed hormesis under Ag+ treatments.•Significant lipid peroxidation promoted by elevated Ag+ doses was observed.•Microstructure of red clover was obviously damaged by prolonged exposure to Ag+.•Altered RAPD fingerprint evidenced Ag+ damage to the genetic material.•Red clover retained on approximately 92.20% of the total Ag absorbed in the roots.
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