Papers by Keyword: Dynamic Fracture

Abstract: The purpose of this study is to compare the impact strength of epoxy composites made of basalt fiber reinforced polymer (BFRP) with those that have nanoclay filler. The matrix materials were Epoxy resin (LY556) and Hardener (HY951), the reinforcing material was basalt fiber, and the filler was warmed montmorillonite nanoclay with a volume percentage of 4%. nanoclay was preheated to 45°C for 40 minutes. The fiber of basalt The control group is epoxy composite (N=20). An experimental group (N=20) of epoxy composite reinforced with basalt fiber and 4% nanoclay filler is created using the hand layup technique. The two groups samples are tested. Results are analyzed using the SPSS-V26 statistical tool, the basalt fiber with 4% volume fraction of warmed nanoclay filler epoxy composite shows the better impact strength, the mean significant difference is p<0.048. The impact strength of BFRP composites containing 4% volume fraction of nanoclay is 9.14% higher than that of BFRP composites without filler, according to the study's limitations.

Abstract: This work discusses the efficiency of six strategies for the numerical solution of the coupled system of partial differential equations that arise from a phase field description of dynamic fracture. Efficient numerical treatment of the dynamic phase field fracture model is a prerequisite for the simulation of failure due to brittle fracture in realistic scenarios such as manufacturing.Firstly, the phase field description of fracturing of brittle solids is introduced. Afterwards, three monolithic as well as three staggered finite element solution strategies are outlined and their performance is studied in two benchmark problems.

Abstract: Ballistic performance has been studied by impacting a long rod projectile into a bulk glass material and a layered specimen. The shock wave interaction on the material boundaries showed that it greatly influences the fracture configuration of glass material. A high speed photographic technique was applied in the experiment to observe the shock wave interaction and damage evolution in the bulk material. Transparent BK7 glass was used as the main material to observe the dynamic fracture phenomena. The depth of penetration (DOP) was measured to assess the ballistic efficiency of the bulk specimen compared with specimens that consisted of selected inter-layer materials, specifically rubber and a steel plate. The obtained results show that the use of a lower impedance material as an inter-layer is effective to enhance the ballistic performance while reducing the shock amplitude and delaying the wave propagation. These findings are in good agreement with the results of a numerical analysis using AUTODYN.

Abstract: In this paper we present a family of gradient-enhanced continuum damage models which can be viewed as a regularization of the variational approach to fracture capable of predicting in a unified framework the onset and space-time dynamic propagation (growth, kinking, branching, arrest) of complex cracks in quasi-brittle materials under severe dynamic loading. The dynamic evolution problem for a general class of such damage models is formulated as a variational inequality involving the action integral of a generalized Lagrangian and its physical interpretation is given. Finite-element based implementation is then detailed and mathematical optimization methods are directly used at the structural scale exploiting fully the variational nature of the formulation. Finally, the link with the classical dynamic Griffith theory and with the original quasi-static model as well as various dynamic fracture phenomena are illustrated by representative numerical examples in quantitative accordance with theoretical or experimental results.

Abstract: Multiscale computer simulation approach has been applied to research mechanisms of failure in ceramic nanostructured ceramics under dynamic loading. The obtained experimental and theoretical data indicate quasi-brittle fracture of nanostructured ZrB₂ ceramics under dynamic compression and tension. Damage nucleation and accumulation in quasi brittle nanostructured ceramics were simulated under impact loadings. Fracture of nanostructured ultra-high temperature ceramics under pulse and shock-wave loadings is provided by fast processes of intercrystalline brittle fracture and relatively slow processes of quasi-brittle failure via growth and coalescence of opened microcracks. For nanostructures ZrB₂ ceramics with porosity of 7 %, the compressive strength at strain rate of 1800 s^-1 is equal to 2440±50 MPa, the tensile strength at strain rate of 300 s^-1 is equal to 155±20 MPa.

Abstract: Simulation of dynamic crack growth under quasistatic loading was performed using finite element method with embedded incubation time fracture criterion [. Experimental data, used for comparison was taken from [. ANSYS finite element software package was used in order to receive FEM solutions. The fracture criterion was implemented as an external procedure written in C++. The developed model is not using and trimming parameters. Only initial experimental conditions and material properties measured in separate experiments are used. Received dependencies for crack velocities as a function of time closely follow those observed in experiments by J.Finberg. Simulation results provide a possibility to conclude that the incubation time approach is an effective method to predict fracture initiation as well as crack propagation at various loading rates. Dependencies of an instant crack velocity on the current level of stress intensity factor received in this work for quasistatic loads and in [ for high-rate loads is discussed and compared to those experimentally observed by K. Ravi-Chandar and W.G. Knauss [ and J. Finberg [.

Abstract: Dynamic fracture of ductile metals at different strain rates and temperatures is studied via molecular dynamic simulations. The results show that both increase of temperature and decrease of strain rate reduce the yield strength, but the stress-strain curves separate prior to yield point at different temperatures. Both increase of temperature and strain rate shorten the duration of the stage of dislocation nucleation and slip. The stress-strain curves for various materials indicate that void nucleation needs not only lower yield strength but also lower fault energy. After the yield point, initially some defect clusters form along the loading direction. With the increasing of strain, small dislocation loops nucleate from some larger defect clusters, then quickly multiply and move on slip plane. When the stress exceeds a critical value, some voids nucleate in dislocation aggregation regions. The incipient void shapes are clavate and void distributions predominantly are along the perpendicular directions of tensile loading. Nucleated voids gradually grow into spherical-like shapes via emitting dislocations.

Abstract: A fine-grained granitic rock is utilized to study the effect of dynamic strain rates on failure response theoretically. Theoretical investigation employs a model that combines dynamic fracture criterion and damage mechanics theory. We simulated the damage evolution and the strain rate evolution when the rock failed under a dynamic load.

Abstract: For the structure failure of pressurized cylindrical shell under laser irradiation, studied with axial semi-elliptical surface crack of cylindrical shell under the combined action of laser radiation and pressure, analysis of its thermal force coupling of stress and material for the 30CrMnSiA steel. According to of static fracture toughness and based on theof estimated impact dynamic fracture toughness, the application of finite element method to study the fracture problem under dynamic load. Analyzing the crack initiation propagation and static dynamic initiation based on fracture criterion and dynamic fracture criterion for crack initiation propagation, provides a useful research of the analysis to a certain extent on the structure in thermal force coupling failure mechanism.

Abstract: The behavior of concrete structures is strongly influenced by the loading rate. Compared to quasi-static loading concrete loaded by impact loading acts in a different way. First, there is a strain-rate influence on strength, stiffness, and ductility, and, second, there are inertia forces activated. Both influences are clearly demonstrated in experiments. For concrete structures, which exhibit damage and fracture phenomena, the failure mode and cracking pattern depend on loading rate. Moreover, theoretical and experimental investigations indicate that after the crack reaches critical speed of propagation there is crack branching. The present paper focuses on 3D finite-element study of the crack propagation of the concrete compact tension specimen. The rate sensitive microplane model is used as a constitutive law for concrete. The strain-rate influence is captured by the activation energy theory. Inertia forces are implicitly accounted for through dynamic finite element analysis. The results of the study show that the fracture of the specimen strongly depends on the loading rate. For relatively low loading rates there is a single crack due to the mode-I fracture. However, with the increase of loading rate crack branching is observed. Up to certain threshold (critical) loading rate the maximal crack velocity increases with increase of loading rate, however, for higher loading rates maximal velocity of the crack propagation becomes independent of the loading rate. The critical crack velocity at the onset of crack branching is found to be approximately 500 to 600 m/s.