Various Types Of Dynamic Loading Research Articles

The Experimental study of plastic strain localization in the AMg6 alloy under various types of dynamic loads

This study is concerned with substantiation of one of the mechanisms of plastic strain localization under high rate loading associated with discontinuous processes in the defect structure of materials. To this end, a series of experiments were carried out to study the localization of plastic strain in specimens of the AMg6 alloy subject to high rate loads on a split Hopkinson-Kolsky bar and during target perforation tests. The temperature fields generated during the plastic deformation tests aimed to identify the characteristic stages of strain localization were investigated "in-situ" using a high-speed infrared camera CEDIP Silver 450M. The values of temperatures in the strain localization zone indicate that in the AMg6 alloy subject to dynamic loads the mechanism of strain localization caused by thermoplastic instability is not realized. After testing of specially-shaped specimens, their surface relief was explored using an optical interferometer-profilometer NewView-5010 with a subsequent processing of the obtained 3D data of the deformation relief and computation of the scale invariant (Hurst exponent) and the spatial scale of the region displaying a correlated behavior of mesodefects. The results of experimental studies on dynamic loading with a subsequent investigation of the temperature fields, the study of the surface relief of deformed specimens suggest that one of the mechanisms of plastic strain localization in the AMg6 alloy under the realized loading conditions is caused by jump processes in the defect structure of the material.

Features of the Polymethyl Methacrylate Destruction Process by Various Types of Dynamic Loading

The paper presents a comparative analysis of the dynamic loading of a polymethyl methacrylate (PMMA) target by a polyethylene (PE) projectile exposed to laser radiation with similar initial energy characteristics of the projectile and the laser pulse. The similarities and differences in the mechanisms of the target's response and its destruction to high-speed mechanical and laser action are shown. A higher efficiency of laser irradiation in the destruction of PMMA was found, and the conditions for the transition of the fracture mechanism from brittle to elastic-plastic were shown.

Connecting mem-models with classical theories

A family of mem-models, including the mem-dashpots, mem-springs, and most recently, mem-inerters, is emerging as a new and powerful way of capturing complex nonlinear behaviors of materials and systems under various types of dynamic loads involving different frequency, amplitude, and loading histories (e.g., hysteresis). Under the framework of nonlinear state-space representation and hybrid dynamical systems, mem-springs may be formulated to effectively represent an inherent degradation of material state. It is shown in this study, for the first time, how the absement (time integral of strain/displacement), a signature state variable for a mem-spring, can be connected with the damage variable, a key quantity in continuum damage mechanics. The generalized momentum (time integral of stress), on the other hand, is shown to be efficient in modeling strain ratcheting via the concept of mem-dashpot. It is also shown in this study, for the first time, how two formulations of the memcapacitive system models (for mem-springs) are special cases of the Preisach model.

Mineral-Bonded Composites for Enhanced Structural Impact Safety – A New Research Training Group GRK 2250 of the German Research Society

Abstract Existing concrete or reinforced concrete structures feature, as a rule, a relatively low resistance to various types of dynamic loading, such as earthquake, impact or blast. This makes it extremely important to develop and propose effective and feasible solutions for strengthening the structures prone to such loading. The contribution will provide an overview of the Research Training Group GRK 2250 “Mineral-bonded composites for enhanced structural impact safety” established in 2017 by the German Research Society (DFG) at the TU Dresden. The goal of GRK 2250 is to bring substantial improvements in the impact resistance of existing buildings by applying thin layers of strengthening material. By using innovative, mineral-bonded composites, public safety and the reliability of vitally important infrastructure should be significantly enhanced. The scientific basis to be developed will additionally enable to build new, impact resistant structures economically and ecologically.

Control performance evaluation of semi-active tmd subjected to various types of loads

Many types of tuned mass dampers (TMDs), such as active TMDs, multiple TMDs, hybrid TMDs, semi-active TMDs etc., have been proposed to effectively reduce the dynamic responses of a structure. Control performance of a conventional TMD subjected to various types of dynamic loads has been widely studied to date. Although it is known that control performance of a semi-active TMD is better than that of a conventional TMD, control performance of a semi-active TMD subjected to various types of dynamic loads has not been fully studied. Therefore, control performance of a semi-active TMD has been systematically evaluated in this study. To this end, an idealized variable damping device and a magnetorheological (MR) damper are used as semi-active dampers. These semi-active dampers can change the properties of TMDs in real time based on the dynamic responses of a structure. The control performance of STMD is investigated with respect to various types of excitation by numerical simulation. Groundhook control algorithm is used to appropriately modulate the damping force of semi-active dampers. The control effectiveness between STMD and a conventional passive TMD, both under harmonic and random excitations, is evaluated and compared for a single-degree-of-freedom (SDOF) structure. Excitations are applied to the structure as a dynamic force and ground motion, respectively. The numerical studies showed that the control effectiveness of STMD is significantly superior to that of the passive TMD, regardless of the type of excitations.

Determination of Johnson cook material and failure model constants and numerical modelling of Charpy impact test of armour steel

The behaviour of typical armour steel material under large strains, high strain rates and elevated temperatures needs to be investigated to analyse and reliably predict its response to various types of dynamic loading like impact. An empirical constitutive relation developed by Johnson and Cook (J–C) is widely used to capture strain rate sensitivity of the metals. A failure model proposed by Johnson and Cook is used to model the damage evolution and predict failure in many engineering materials. In this work, model constants of J–C constitutive relation and damage parameters of J–C failure model for a typical armour steel material have been determined experimentally from four types of uniaxial tensile test. Some modifications in the J–C damage model have been suggested and Finite Element simulation of three different tensile tests on armour steel specimens under dynamic strain rate (10−1s−1), high triaxiality and elevated temperature respectively has been done in ABAQUS platform using the modified J–C failure model as user material sub-routine. The simulation results are validated by the experimental data. Thereafter, a moderately high strain rate event viz. Charpy impact test on armour steel specimen has been simulated using J–C material and failure models with the same material parameters. Reasonable agreement between the simulation and experimental results has been achieved.

Nonstationary problem for a bimaterial containing a crack and an interlayer

We consider a dynamic problem of interaction of a plane penny-shaped crack with thin elastic interlayer connecting two identical elastic half spaces. The crack is located in one of the half spaces perpendicularly to the interlayer and the crack faces are subjected to the action of impulsive tensile forces. The thin interlayer is modeled by the conditions of imperfect contact of the half spaces. By using the Fourier transformation with respect to time, we reduce the problem to a Helmholtz-potential-type boundary integral equation for the function of dynamic crack opening displacements. As a result of the numerical solution of this equation and transition to the originals, we get the time dependences of mode-I stress intensity factors in the vicinity of the crack for various types of dynamic loads, ratios of the elastic parameters of the half spaces and the interlayer, and the distance between the crack and the interlayer.

Harmonic differential quadrature-finite differences coupled approaches for geometrically nonlinear static and dynamic analysis of rectangular plates on elastic foundation

The geometrically nonlinear static and dynamic analysis of thin rectangular plates resting on elastic foundation has been studied. Winkler–Pasternak foundation model is considered. Dynamic analogues Von Karman equations are used. The governing nonlinear partial differential equations of the plate are discretized in space and time domains using the harmonic differential quadrature (HDQ) and finite differences (FD) methods, respectively. The analysis provides for both clamped and simply supported plates with immovable inplane boundary conditions at the edges. Various types of dynamic loading, namely a step function, a sinusoidal pulse and an N-wave, are investigated and the results are presented graphically. The accuracy of the proposed HDQ–FD coupled methodology is demonstrated by the numerical examples.

Nonlinear analysis of thin rectangular plates on Winkler–Pasternak elastic foundations by DSC–HDQ methods

This article introduces a coupled methodology for the numerical solution of geometrically nonlinear static and dynamic problem of thin rectangular plates resting on elastic foundation. Winkler–Pasternak two-parameter foundation model is considered. Dynamic analogues Von Karman equations are used. The governing nonlinear partial differential equations of the plate are discretized in space and time domains using the discrete singular convolution (DSC) and harmonic differential quadrature (HDQ) methods, respectively. Two different realizations of singular kernels such as the regularized Shannon’s kernel (RSK) and Lagrange delta (LD) kernel are selected as singular convolution to illustrate the present DSC algorithm. The analysis provides for both clamped and simply supported plates with immovable inplane boundary conditions at the edges. Various types of dynamic loading, namely a step function, a sinusoidal pulse, an N -wave pulse, and a triangular load are investigated and the results are presented graphically. The effects of Winkler and Pasternak foundation parameters, influence of mass of foundation on the response have been investigated. In addition, the influence of damping on the dynamic analysis has been studied. The accuracy of the proposed DSC–HDQ coupled methodology is demonstrated by the numerical examples.

Impact resistance of composite plate

Structures are often subjected to various types of dynamic loads and the need to accurately predict the structural response and reserve capacity under such loading has led to an interest in the properties of composite materials. Fibre reinforcement improves the dynamic behaviour of reinforced concrete and ferro cement under impact loading. This paper reports an experimental investigation of the dynamic behaviour of composite slab panels under impact loads. Impact tests were carried out on various types of fibre-reinforced cement concrete slabs and fibre-reinforced ferro-cement slabs to study the influence of fibres on the energy absorption. The response of all the above specimens were examined and compared. Analytical solutions were obtained from a finite element analysis and the results are also compared.

Impact resistance of composite plate

Structures are often subjected to various types of dynamic loads and the need to accurately predict the structural response and reserve capacity under such loading has led to an interest in the properties of composite materials. Fibre reinforcement improves the dynamic behaviour of reinforced concrete and ferro cement under impact loading. This paper reports an experimental investigation of the dynamic behaviour of composite slab panels under impact loads. Impact tests were carried out on various types of fibre-reinforced cement concrete slabs and fibre-reinforced ferro-cement slabs to study the influence of fibres on the energy absorption. The response of all the above specimens were examined and compared. Analytical solutions were obtained from a finite element analysis and the results are also compared.

Biomechanics of temporo-parietal skull fracture

This paper presents an analysis of research on the biomechanics of head injury with an emphasis on the tolerance of the skull to lateral impacts. The anatomy of this region of the skull is briefly described from a biomechanical perspective. Human cadaver investigations using unembalmed and embalmed and intact and isolated specimens subjected to static and various types of dynamic loading (e.g., drop, impactor) are described. Fracture tolerances in the form of biomechanical variables such as peak force, peak acceleration, and head injury criteria are used in the presentation. Lateral impact data are compared, where possible, with other regions of the cranial vault (e.g., frontal and occipital bones) to provide a perspective on relative variations between different anatomic regions of the human skull. The importance of using appropriate instrumentation to derive injury metrics is underscored to guide future experiments. Relevance A unique advantage of human cadaver tests is the ability to obtain fundamental data for delineating the biomechanics of the structure and establishing tolerance limits. Force–deflection curves and acceleration time histories are used to derive secondary variables such as head injury criteria. These parameters have direct application in safety engineering, for example, in designing vehicular interiors for occupant protection. Differences in regional biomechanical tolerances of the human head have implications in clinical and biomechanical applications.

Vibrations of a complex system with damping under dynamic loading

This paper introduces an analytical-numerical method for solving a problem related to free and forced damping vibrations of a complex system that consists of two plates coupled with a viscoelastic interlayer. On the basis of the designed method, we perform numerical analysis by means of the Timoshenko and Kirchhoff–Love models and investigate new mechanical effects attributable to the action of various types of dynamic loading on the system considered.

Dynamic instability of composite laminated rectangular plates and prismatic plate structures

Periodic dynamic loadings may cause dynamic instability of a structure through parametric resonance. In this paper, a B-spline finite strip method (FSM) is presented for the dynamic instability analysis of composite laminated rectangular plates and prismatic plate structures, based on the use of first-order shear deformation plate theory (SDPT). The equations of motion of a structure are established by using Lagrange's formulation and they are a set of coupled Mathieu equations. The boundary parametric resonance frequencies of the motion are determined by using the method suggested by Bolotin through a novel development which incorporates the Sturm sequence method and the multi-level substructuring technique to achieve reliability, efficiency and accuracy. Various loading patterns, arbitrary lamination and general boundary conditions are accommodated. A variety of numerical applications is presented to test the developed method and to study the dynamic instability behaviour of single plates and of complicated plate structures under various types of dynamic loading. A dynamic instability index (DII) is devised to measure the degree of instability against certain parameters which include the thickness-to-length ratio, the degree of orthotropy, the fibre orientation, the loading pattern and the boundary conditions.

Nonlinear forced vibrations of shallow shells on regular polygonal bases

The nonlinear, large amplitude vibrations of elastic, shallow shells when subjected to transient pressure loading are analyzed in a relatively simple manner. The isoamplitude contour lines approach is used to derive the basic equations for shallow shell vibrations. The coupled system of governing equations thus obtained is solved for shells of regular polygonal planform with various types of dynamic loading. Also, an equivalent analysis in which Berger’s approximation is used is presented and a comparison is made of the results obtained by both methods. Some comparison is also made with previously obtained results, as available in the literature. All details are explained by graphs.

Non-linear vibrations of elastic plates subjected to transient pressure loading

The large amplitude vibrations of elastic plates of arbitrary plan form subjected to transient pressure loading are analyzed in a relatively simple fashion by using the Berger method in conjunction with the iso-amplitude contour lines method. The analysis provides for both clamped and simply supported edge conditions. By way of illustration, the large amplitude response of elliptical plates under various types of dynamic loading, namely a step function, a sinusoidal pulse and an N-wave, is investigated and the results are presented graphically. Some comparison is made with previously obtained results for circular plates, as available in the literature.

Strength of cylindrical shells of laminar composites under dynamic loading

The methods described in the present review paper for the computation of cylindrical shells of laminar composites under various types of dynamic loads make it possible to calculate the stress-strain state at any point of the body of the shell at an arbitrary time and to determine the time of the first failure of a layer (including fatigue failure) using strength criterion of an anisotropic body for the case of a plane stressed state, and also the location of the first flaw in the shell. This makes it possible to determine the magnitude of the applied pulse (the amplitude of a pulsed loading), or the amplitude of a vibratory loading for which the first centers of failure appear in the design.

Investigation of dynamic errors in weighing loads in motion

The above theoretical investigations, a brief analysis of the dynamic errors in weighing a moving load and subsequent test results have shown that the method of measuring the load at the instants when the effort applied to the strain gauges passes through its mean-amplitude value provides measurements with an acceptable precision for various types of dynamic loading. The cited relationships and formulas can be used for evaluating systematic dynamic errors for various types of load oscillations, and thus for predicting the efficiency of any given method in forming a control pulse for reading the weight of the load.

Effects of Low-Frequency Vibrations on Man

The physical responses of the human body to frequencies below approximately 50 cps can be described by analyzing the body as a lumped parameter system. Recent refinements of measurement techniques allow more precise determination of this mechanical model and of many of its parameters, its resonances and mechanical impedances. This model is useful in studying the dynamics of the body exposed to various types of dynamic loads: whole body vibration, transient acceleration, blast exposure, respirator excitation, and rapid decompression. The response of the thorax-abdomen system is discussed in detail. These studies are valuable as guides in future experimentation, in the interpretation of various types of biological effects, and in developing and understanding protective measures. The limits of linearity of the various components of the system and data on tissue strength are still unknown. The various effects limiting voluntary human tolerance to vibrations and their connection with the body's physical responses are reviewed. The inadequacy of existing data for determining definitive vibration exposure criteria for practical application is discussed.