Dynamic Stress State Research Articles

Analysis of dynamics of laminated glass composite panels with different glass curvature under impact loading

The article presents the results of the analysis of shallow shell laminated glass composites dynamic state under impact loading. The study considers modelling of a smooth steel ball drop on laminated glass with different curvature of laminate. The work includes modelling the composite in a three-dimensional setting as part of a physical linear-elastic state. The interaction of the ball and the laminate was carried out in the framework of solving the problem of one-way contact by the "surface to surface" (STS) algorithm. The resistance caused by air during impact was neglected. The aim of the work is to study the dependence of laminated glass dynamic deformation on the composite curvature. The article carries out modelling of behavior of the laminated glass samples with PVB interlayer using transient analysis. The study performs computations using a finite element method (FEM) using hexagonal FE with 8 nodes with 3 degrees of freedom in each within a 3D modelling and explicit dynamics approach in modern computer-aided engineering (CAE) software. The investigation includes a mesh-size convergence analysis. The work carries out the dynamic strain and stress state analysis in laminated glass with different parameters of laminate curvature, derives the results of deformation and strain in characteristic points at different time moments, plots the dependence graphs of deformation and strain on the parameter of glass curvature.

Experimental study on dynamic biaxial tension-compression properties of hydraulic concrete

ABSTRACT Most hydraulic concrete structures are in complex stress state. In order to study the effect of dynamic action on properties of hydraulic concrete under biaxial tension-compression, hydraulic concrete specimens were subjected to dynamic biaxial tension-compression tests were conducted at 6 different tension-compression ratios of 0 (uniaxial compression), 0.05:-1, 0.1:-1, 0.25:-1, 0.5:-1, ∞ (uniaxial tension) as well as 4 different strain rates of 10−5/s, 10−4/s, 10−3/s and 10−2/s. The failure mode, ultimate strength, peak strain and stress-strain curve under different tension-compression ratios and strain rates were measured. According to test data, the ultimate strength, as well as deformation properties, was analysed in terms of tension-compression ratio and strain rate. The failure criterions of hydraulic concrete under dynamic biaxial tension-compression stress state were established in principal stress space and octahedral stress space, respectively, providing experimental and theoretical reference for the design and maintenance of hydraulic structures. The results of the research on the ultimate strength and failure criterion of ordinary concrete, wet sieve concrete and air-entrained concrete under biaxial stress state were compared with the experimental results of this paper, proving the feasibility of the failure criterion proposed in this paper.

Dynamic stress state of underground pipelines at junctions

A one-dimensional statement of unsteady wave problem of a longitudinal monochromatic wave propagation and reflection from a rigid stationary barrier to which an underground pipeline abuts is given. The linear viscoelastic Eyring model, which describes limited creep and limited relaxation, is taken as the pipeline strain law. Eyring model allows us to describe the behavior of underground steel and polymer pipelines under dynamic loading. The problem is solved numerically using the theory of characteristics, followed by the finite difference method in an implicit scheme. Numerical solutions obtained in the form of dependences of plane wave parameters: longitudinal stress, velocity and strain for fixed sections of the pipeline are analyzed in the paper. An analysis of changes in these wave parameters shows that at high frequencies of dynamic load generating the wave, the stress amplitude in the pipeline increases by two or more times compared to the load amplitude. This is due to the superposition of incident and reflected waves in the pipeline and to a high loading rate of the pipeline. At low frequencies of dynamic loading, such an increase is not observed due to the low loading rate. The obtained numerical solutions allow choosing the statement of problems on dynamic stress state of an underground pipeline depending on the frequency of incident wave. It is shown that the greatest longitudinal stress in an underground pipeline arises in points (sections) close to its connection with a rigid stationary solid body.

Quantification of Fatigue Damage for Structural Details in Slender Coastal Bridges Using Machine Learning-Based Methods

Abstract Exposed to the challenging coastal environment, slender bridges could experience significant dynamic responses and complex stress states resulting from the coupled dynamic impacts of wind,...

Dynamic stress state around shallow-buried cavity under transient P wave loads in different conditions

The failure of underground structure is always caused by local stress redistribution resulted from transient impact loads. An analytical model is established and solved by using the complex variable function method to illustrate the dynamic stress concentration around a shallow-buried cavity under transient P wave loads. The transient wave response is attained as an integration of steady-state wave response in circular frequency domain. By adopting a Butterworth filter, the jump points in the dynamic stress concentration factor (DSCF) curve which is not in line with the overall trend is filtered out to obtain more reasonable results. The convergence and accuracy of the solutions are verified and discussed in detail. DSCF distributions of high wavenumber incidences differ from that of low wavenumber incidences significantly in amplitudes and distribution patterns. The effects of the cavity depth, incidence angle and position of wave peak on DSCF distributions are illustrated.

Fracture Evaluation and Dynamic Stress Concentration of Granite Specimens Containing Elliptic Cavity under Dynamic Loading

The Split-Hopkinson pressure bar (SHPB) was used to determine the fracture characteristics of a long bar rock specimen with an elliptical cavity under different axial ratios and dip angles. A high speed camera was applied to record the fracturing process of the granite specimen around the cavity. The experimental results showed that the fracture characteristics around the elliptical cavity were closely related to the axial ratio and dip angle. A three-dimensional numerical model was established using LS-DYNA to quantitatively analyze the dynamic stress state around the cavity. The numerical results indicate that the dip angle and axial ratio of the elliptical cavity significantly affected the dynamic stress concentration factor (DSCF), then affected the rock failure. The location of higher DSCF led to a higher possibility of spalling failure. The maximum DSCF remarkably decreased with a decreasing dip angle and increased the axial ratio. In the dynamic loading propagate process, the stress concentration distribution around the cavity formed by a compression stress wave had a certain damaging effect on the destruction of rock around the cavity, and the stress concentration generated by the tensile stress wave was the main factor of the rock fracture, which was most notable in the peak area of the stress concentration.

ПРОГНОЗИРОВАНИЕ УСТАЛОСТНОЙ ДОЛГОВЕЧНОСТИ НЕСУЩЕЙ КОНСТРУКЦИИ КУЗОВА ПАССАЖИРСКОГО ВАГОНА С ПЕРФОРИРОВАННЫМИ ПОДКРЕПЛЯЮЩИМИ ЭЛЕМЕНТАМИ

The purpose of the work is a fatigue life assessment for bearing structures of passenger car bodies with perforated supporting elements through the methods of computer mathematical modeling. 
 The fulfilled analysis of investigations in the field of the fatigue life assessment for welded bearing structures of car bodies has shown that its assessment should be carried out in a dynamic setting with the development of a spatial dynamic model of a car body. 
 The fatigue life assessment in the most loaded areas of perforated supporting elements in car bodies was carried out with the use of two procedures: Serensen-Kogaev procedure and Bolotin one. There are considered ten versions of supporting element perforation in a passenger car body. The development of finite element models of car bodies with the mentioned options is carried out by the example of the body of a domestic passenger car. On the basis of the design strength computation results there are defined three most loaded areas of perforated supporting elements. The refined assessment of a dynamic stressed state of the areas under investigations is carried out through the method of an area successive accentuation. 
 As a result of the investigation there are obtained life values of the most loaded areas for a passenger car body bearing structure for all perforation options under consideration. 
 The results obtained confirm passenger car operation safety with the offered option of perforation and are evidence of the purposefulness in the application of the procedure offered for the fatigue life prediction of similar bearing structures.

Investigation of Rail Deformation and Stress Wave Propagation in the ISL-NGL60 Railgun

Railgun performance requires a low-resistance electric gliding contact between the rails and the armature. The electromagnetic forces, which accelerate the launch package (0.7 to 3 kg mass) up to more than 2000 m/s, are acting on the rails as repulsive forces. Therefore, the rails of the NGL60 electromagnetic gun, with caliber 60 $\times$ 60 mm2, are held in their position by an arrangement of discrete steel bolts, further by beams and plates made of glass fiber reinforced plastic, as well as by stiffening metal plates. The highly dynamic electromagnetic forces generate stress waves and elastic rail deformation that might contribute to contact transition between the rails and the armature. If the rail deformation enters the plastic domain, the rail geometry may be altered in an unfavorable way for subsequent shots. For our numerical investigation, we used the multiphysics finite-element computation code LS-DYNA to simulate a railgun projectile launch with a moving armature by injecting an electric current into the rails. It is therefore possible to study the dynamic deformations during the launch and get insight in the dynamic stress states. The material models for the rails and for the armature take into account elastic-plastic stress-strain behavior as well as strain rate sensitivity. We expect to simulate launch dynamics with higher accuracy than previously presented models with a nonmoving armature. The principal objective of the study is to show that this procedure is capable of effectively optimizing the structural behavior of the rails inside the barrel.

Ivestigation of the Dynamic Stress State of Foam Media in Cosserat Elasticity

Abstract The paper presents studies on the application of the boundary integral equation method for investigation of dynamic stress state of foam media with tunnel cavities in Cosserat continuum. For the solution of the non-stationary problem, the Fourier transform for time variable was used. The potential representations of Fourier transform displacements and microrotations are written. The fundamental functions of displacements and microrotations for the two-dimensional case of Cosserat continuum are built. Thus, the fundamental functions of displacement for the time-domain problem are derived as the functions of the two-dimensional isotropic continuum and the functions, which are responsible for the effect of shear-rotation deformations. The method of mechanical quadrature is applied for numerical calculations. Numerical example shows the comparison of distribution of dynamic stresses in the foam medium with the cavity under the action of impulse load accounting for the shear-rotation deformations effect and without accounting for this effect.

Numerical simulation of missile warhead operation

Numerical simulation of a missile warhead dynamic fracture is considered. The design of the warhead basic units is treated. The approach for simulations of the warhead fracture in software ANSYS is proposed. This approach is split on three stages. (I). The analysis of the static stress-strain state of the warhead, which is arisen owing to its assembling. (II). Calculations of the dynamic stress state of the structure. (III). Analysis of dynamic fracture of the most loaded units. The parameters of the warhead are chosen in order to a fracture takes place in the structure specified area.

A strain-rate-dependent damage model for evaluating the low velocity impact induced damage of composite laminates

Low velocity impact (LVI) has always been a potential threaten to composite structures. This out-of-plane dynamic impact load easily leads to a dramatic increase of the strain state in the material transverse plane, which can affect the dynamic stress state and damage evolution of the composite laminate, especially for LVI with a relatively high energy. However, the strain rate effect was always neglected in existing investigations, thus introducing inevitable errors in numerical predictions for engineering practices. To accurately capture the failure process of composite laminates under LVI, a three-dimensional strain-rate-dependent damage model was proposed. This model was composed of three parts: a modified stress–strain relationship for composites under a dynamic stress state; a strain-rate-dependent progressive damage model to evaluate the intra-laminar damage; and a cohesive zone model to examine the inter-laminar delamination. LVI tests with different impact energies were conducted to provide validating data. It is shown that the numerical results from the strain-rate-dependent damage model are highly consistent with the experimental outcomes. The contact force history curves, intra- and inter-laminar damage evolution process are found to be strain rate dependent, and thus the numerical errors predicted by the strain-rate-independent damage model significantly increase with the increment of the applied impact energy, which is unacceptable in practice for LVI with relatively high impact energies.

Problems of interaction longitudinal shear waves with V-shape tunnels defect

The problem of determining the two-dimensional dynamic stress state near a tunnel defect of V-shaped cross-section is solved. The defect is located in an infinite elastic medium, where harmonic longitudinal shear waves are propagating. The initial problem is reduced to a system of two singular integral or integro-differential equations with fixed singularities. A numerical method for solving these systems with regard to the true asymptotics of the unknown functions is developed.

Effect of polycarboxylate ether superplasticizer (PCE) on dynamic yield stress, thixotropy and flocculation state of fresh cement pastes in consideration of the Critical Micelle Concentration (CMC)

Polycarboxylate ether surperplasticizer (PCE) has been commonly used and studied to enhance flowability of cementitious materials. However, the effect of PCE addition on thixotropy and flocculation state has not gained enough attention. In this study, Focused Beam Reflectance Measurement (FBRM)-rheometer is coupled. The coupled setup could simultaneously measure both flocculation states in terms of chord length distribution of cement particles/agglomerates and rheological properties including dynamic yield stress and thixotropy. The effect of various PCE additions is explored, firstly by measuring the adsorption of PCE surfactants and the concentration of PCE surfactants in cement pore solution. It is found that the effect of PCE addition on dynamic yield stress, thixotropy and chord length distribution of paste particles/agglomerates are all bi-fold. The turning point is the Critical Micelle Concentration in cement pore solution. Results of more agglomerated flocculation states at low PCE addition are measured for the first time and further discussed.

Investigation of the shock waves impact on the dynamic stress state of medium with the system of tunnel cavities

Розвинено методику дослідження розподілу динамічних напружень у пружних тілах з системами тунельних порожнин на основі інтегрального та дискретного перетворення Фур’є за часом. В області Фур’є-зображень використання методу граничних інтегральних рівнянь та апарату теорії функції комплексної змінної дало можливість розробити ефективний алгоритм визначення динамічного напруженого стану для тіл з порожнинами практично довільного перерізу. На основі запропонованої методики проведено числові розрахунки динамічної концентрації напружень на границі тунельних порожнин кругового та еліптичного перерізу й побудовано часові розподіли динамічних напружень за дії ударного навантаження. Вивчено вплив відбитих хвиль на динамічний напружений стан у тунельних порожнинах.

Stress State of Foam Media with Tunnel Openings Under Non-Stationary Dynamic Loading

The dynamic stress state of the bodies considering the couple stresses using the Fourier transformation and method of integral equations has been investigated. The obtained results are in the agreement with the basic concepts of wave mechanics. The developed procedure allows one to investigate the non-stationary dynamic processes in synthetic materials with openings of the virtually free section. The opening geometry effect on the distribution of dynamic loads in foam media has been studied

Stress State Simulation and Durability Evaluation of a Spot-Welded Joint in Case of Random Vibration

In this paper the authors present the methodology and results of computational studies of the stress state and the evaluation of the construction durability with multipoint welded joints in the event of random vibration. A special feature of the technique is a detailed simulation of the stress state in the most stressed connection junctions, taking into account the change in the properties of the base material during welding. The empirical equations between the microhardness and the material yield point in the local zone of the welded point are used for this. The developed technique for numerical simulation of the dynamic stressed state of a construction with a point-welded joints can be used to assess the vibration strength of such constructions under conditions of random loading.

Confinement device to assess dynamic crushability of wood material

Cellular materials such as wood are widely and advantageously used as shock absorbers in various transport applications. The design and manufacturing of structures made of these materials require the knowledge of their dynamic compressive properties at various strain rates and stress states. Therefore, it is challenging to conduct dynamic multiaxial stress state experiments and especially on split-Hopkinson pressure bar apparatus where stress hardening increases as a function of velocity. This paper presents the so-called verification and validation methodology for confining solutions dedicated to impact on viscoelastic split-Hopkinson pressure bar system with large diameter bars. The method is a hybrid approach combining finite element analysis and an original experimental validation. Based on finite element results, particular attention is given to the mass, the material and the geometry to minimize the confining device influence on the propagation of elastic waves and thus on the material response of the tested specimens. It is essential to avoid spurious reflected waves at the new interfaces of the system in order to ensure the validity of the experimentation. The numerically predicted solutions are experimentally validated and preliminary results in the context of dynamic loadings using wood material are presented.

Characterization of the small-strain dynamic behaviour of silty sands; contribution of silica non-plastic fines content

Dynamic properties of soils at very small strains are of particular interest for geotechnical engineers for the characterization of the behaviour of earth structures subjected to a variety of static and dynamic stress states. This study reports on the small-strain dynamic properties of silty sand with particular emphasis on the effect of non-plastic fines content on the small-strain shear modulus (Gmax) and material damping (Ds,min). Several clean sands with a wide range of grain size distribution and particle shape are mixed with different percentages of a silica non-plastic silt. The laboratory created samples are subjected to torsional resonant column tests with small-strain shear moduli and damping ratios measured along an isotropic stress path. It is shown that at low percentages of fines content, there is a significant difference between the dynamic properties of the various samples due to the different characteristics of the sand portion of the mixtures. However this variance diminishes as the fines content increases and the soil behaviour becomes mainly silt-dominant, rendering no significant influence of different sand properties on the small-strain shear modulus and damping ratio. Using the experimental results, new expressions for the prediction of small-strain shear modulus and small-strain damping ratio of non-plastic silty sands are developed accounting for the percentage of silt and the characteristics of the sand portion.

Dynamic Stress Concentration at the Boundary of an Incision at the Plate Under the Action of Weak Shock Waves

Abstract This paper proposes the novel technique for analysis of dynamic stress state of multi-connected infinite plates under the action of weak shock waves. For solution of the problem it uses the integral and discrete Fourier transforms. Calculation of transformed dynamic stresses at the incisions of plates is held using the boundary-integral equation method and the theory of complex variable functions. The numerical implementation of the developed algorithm is based on the method of mechanical quadratures and collocation technique. For calculation of originals of the dynamic stresses it uses modified discrete Fourier transform. The algorithm is effective in the analysis of the dynamic stress state of defective plates.

Relationship between powder characteristics and part properties in laser beam melting of Ti–6Al–4V, and implications on quality

The technology of laser beam melting (LBM) has lately become a true option for series production of functional end products. Metallic materials such as steel, aluminum, and titanium alloys may be processed to fully dense parts with mechanical properties meeting or even exceeding their conventionally manufactured counterparts. However, the use of LBM for industrial applications also requires reliable quality assurance methods along the entire process chain. Besides monitoring and controlling the LBM process itself, this implicates a thorough understanding of the relationship between the powder feedstock characteristics and the properties of the manufactured parts. This paper provides an in-depth analysis of how the characteristics of different Ti–6Al–4V powder feedstocks influence the usual quality criteria of parts. Typical characteristics of virgin powders from three different manufacturing routes, namely gas atomization, plasma atomization, and induction plasma spheroidization, are studied. Besides the investigation of particle morphology, particle size distribution, and chemical composition, powder flowability is determined using different measurement methods. Applying methods such as Hall flowmeter, angle of repose, Hausner ratio, avalanche angle, powder rheology, and shear tests, the powders are tested under static and dynamic stress states. From the different feedstocks, specimens are manufactured and the part properties such as density and static strength are determined. Correlation between powder characteristics and the resulting part properties is investigated. Depending on the different powder analyzation methods, recommendations for quality assurance are derived. It is shown that quality assurance of Ti–6Al–4V powder for LBM is a complex task. Powder material quality for this process cannot be ensured using a single measurement parameter or method as it is a result of the interactions between various properties. Such being the case, the determination of powder flowability leads to ambiguous results, irrespective of the selected measurement method. Presumably, the application of powder with good flowability according to a specific test will regularly result in parts with high density and acceptable mechanical properties. However, powder with comparably low flowability might also be applicable for the manufacturing of parts that meet the required quality criteria. As a consequence, solely employing a flowability test for powder quality assurance would possibly reject a number of powder batches that would turn out to be suitable for the LBM process.