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One of the main problems in control is that the overwhelming number of physical quantities cannot be measured directly. Hence, there arise so-called inverse problems on the determination of physical quantities from the results of their manifestations. In the mechanics of a deformable solid there is a problem of obtaining material properties at all stages of deformation and especially at the overcritical stage. In this paper, we formulate and solve the inverse problem of finding the tensile diagram of a material element from the diagram of the dependence of the bending moment on the curvature of a rectangular beam under pure bending. [ABSTRACT FROM AUTHOR]

The paper presents a shear strength model used to evaluate information of interest from shock experiments aimed at studying the properties of the hardened 30KhGSA steel and the MA14 magnesium alloy subjected to low- and high-intensity loadings. The model parameters are adjusted by experimental deformation curves obtained from static and dynamic tests at different temperatures and the data from shock experiments to account for strength variation at high strain rates. The simulation of low-intensity loading tests helped to improve the description of elastic-plastic properties and to adjust our failure model. The data from the shock experiments with high-intensity loading of 30KhGSA steel samples and unloading of the shocked samples in window materials were used to verify the phase diagram and the kinetics of direct and inverse phase transitions, and to determine more exactly how the changed phase state influences the strength. The model presented here has allowed us to reproduce the complicated strength behavior of the MA14 alloy at different loading intensities. [ABSTRACT FROM AUTHOR]

This paper deals with the development and approbation of a computational model of damage accumulation in a vertical steel tank at the non-uniform foundation subsidence. The object of research is structure behavior at the survivability stage, namely, the character and sequence of damage initiation and accumulation (elastic-plastic strain, bottom and wall buckling) in the tank structure. [ABSTRACT FROM AUTHOR]

Residual stress in layered composites significantly affects their mechanical properties. One of the most important tasks in the sphere of experimental mechanics is the development of effective methods for the accurate determination of residual stress values. This paper describes a modified destructive testing method implemented through layer-by-layer stitching. It differs from previous analogous methods by the use of electronic speckle pattern interferometry to measure the deformation response of a given sample. The interpretation of the initial experimental data in “stress terms” was carried out based on modeling through the use of the finite element method (FEM). [ABSTRACT FROM AUTHOR]

In the present paper, the investigation results on the strain dependence of the Rayleigh wave velocity are presented. Plane dog-bone metal specimens were deformed by tension at a constant strain rate. The specimens were made of low-carbon steel with a carbon content of 0.1% (C10) and 0.2% (C22), martensitic stainless steel X40Cr13, and commercially pure titanium (CP Ti). Discontinuity points in the stress dependences of ultrasonic velocity and damping were found. These points are considered to be ultrasonic criteria for the stage change in the deformation process. [ABSTRACT FROM AUTHOR]

This paper deals with an ultrasonic technique based on the measurement of acoustic birefringence of shear elastic waves for the evaluation of plasticity margin of an aluminum alloy operating in the conditions of Far North and the Arctic. We tested flat samples under uniaxial static tension at room and subzero temperatures. Besides, we performed ultrasonic measurements. We have found that acoustic birefringence monotonically changes during plastic deformation. The effect of plastic strain on the acoustic birefringence is associated with damage accumulation and texture change. As a result of the study, we have obtained a correlation equation allowing us to estimate the plasticity margin of the aluminum alloy at a subzero temperature, as well as at room temperature, using the measurement results of acoustic birefringence. [ABSTRACT FROM AUTHOR]

The paper presents first results of obtaining metal-matrix composites based on severe plastic deformation by shear under pressure of layered Al and Cu components. Three-layer composites with different alternation of layers, i.e. Al-Cu-Al and Cu-Al-Cu, were processed by constrained high pressure torsion to produce monolithic disk-shaped samples without pores. Analysis of the macroscopic homogeneity showed that different alternation of layers led to varying degrees of mixing of the starting components. [ABSTRACT FROM AUTHOR]

The paper presents an automated system for monitoring the deformation state of a building complex. The measurement unit of the system records the vertical displacements of a number of bearing columns using the hydroleveling method. In the analytical block, numerical modeling of deformation processes in the subsoil–foundation– building system is performed. The information on the foundation settling obtained during monitoring is used to specify the boundary conditions for modeling the stress-strain state of the structure. Thus, the deformation response of all structural elements to uneven vertical settling of supporting columns is evaluated. The monitoring system has been working since 2010 and it has demonstrated high efficiency. [ABSTRACT FROM AUTHOR]

In this paper, a method of mechanical impact on an element of a ring frame of a U-shaped cross-section with the aim of opening a closed delamination to a minimum size is considered, which will allow this defect to be detected by the nondestructive X-ray diffraction method, in condition that the loading will not lead to the formation of new defects and further growth of the existing ones. [ABSTRACT FROM AUTHOR]

The paper presents an experimental investigation of the mechanical behavior of specimens made of alumina ceramics prior to catastrophic fracture and the transition to the blow-up mode. Ceramic specimens are tested in three point bending and uniaxial compression tests. The surface velocity of the loaded specimens is registered using a laser Doppler vibrometer. The duration of the stage of a catastrophic increase in the lateral surface velocity prior to fracture is approximately half a millisecond in three-point bending tests and about 0.1 ms in compression tests. [ABSTRACT FROM AUTHOR]

Analysis of design methods for composite beams with curvilinear fiber trajectories is considered in this paper. The novelty of this approach is determined by the fact that traditional composite materials are typically formed using prepregs with rectilinear fibers only. The applications of the results are associated with designing shaped members with a composite structure by using of biomechanical principles [1,2]. One of the problems is evaluation of the effect of fiber misorientation on the stiffness and load carry capacity of a shaped composite element with curvilinear fiber trajectories. An equistrong beam with a constant cross-section area is considered as an example, and it can be produced by forming of a unidirectional fiber bunch impregnated by a polymer matrix. Methods for evaluating the effective elastic modulus for structures with curvilinear fiber trajectories are validated. The misorientation angle range (up to 5 degrees), when a material with required accuracy can be considered as homogeneous, is determined, fiber misorientation being neglected. It is shown that, for beams with a fairly small height-to-width ratio, it is possible to consider only 2D misorientation. [ABSTRACT FROM AUTHOR]

The paper is concerned with the skin effect of plastic deformation, which was discovered circa ninety years ago. The study is carried out with the help of the hydrogen diagnostics. Accumulation of hydrogen is shown to occur due to the dissociation of atmospheric moisture under the process of plastic deformation of metals in a thin surface layer comparable to the grain size. Hydrogen is accumulated in pores and microcracks, whose volume in the surface layer increases hundred-fold. The zones of localization of plastic deformation coincide with the local surface zones of hydrogen storage. The obtained experimental data lead to the conclusion that the surface layer cannot be considered as a continuous medium. [ABSTRACT FROM AUTHOR]

With two structural steels (the steels 50 and 09G2S) as examples, the paper studies the effectiveness of a new method of ultrasonic impact-frictional treatment (UIFT) for the hardening and nanostructuring of the surface layer with the variation of the tilt angle of the vibrating indenter and the treatment environment. It is demonstrated that treatment with tool tilt angles different from 90° and with the absence of a contact liquid results in the formation of a nanostructured surface layer with increased microhardness. [ABSTRACT FROM AUTHOR]

The paper consists of two parts united by the central idea of the random field of the microstructure of the material. The first part addresses a discrete static approach to describing the localization effect of plastic deformation known with the help of finite-element analysis under the assumption that the deformation of each of the grains obeys a bilinear law with a normal distribution of the yield stress over the grains. The result is a surface relief in the form of diagonally directed strips, which allows one to treat the deformed surface as Panin’s "chessboard". The second part is concerned with a dynamic continuum approach to the description of the random microstructure of materials. The problem of the propagation of stochastic waves modeled by waves in media with random elastic and mass properties is solved by means of the integral decomposition of the wave amplitude over the wave numbers. [ABSTRACT FROM AUTHOR]

The paper describes the experimental procedures carried out in order to investigate the rheological properties of carbon fiber reinforced polyetheretherketone (PEEK) and the mechanical properties of injection-molded parts from this material. Four test nozzles have been designed for the investigation of the rheological properties of PEEK. The nozzles containing two pressure sensors and a temperature sensor have been mounted on a 22 Tons injection molding machine. As a result, pressure-time and temperature-time curves have been obtained and then used to calculate the PEEK viscosity as a function of shear rate. Several test specimens have been molded to study the properties of injection-molded parts. First, tension tests have been performed to obtain stress-strain curve and the strength value for PEEK. Then the Young modulus has been experimentally determined using a vibrational method. Flexion tests have allowed to estimate the flexural modulus value. The experimental results obtained in this study can be used to improve the accuracy of injection molding simulation and structural FEM analysis. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

A parallel computational environment for modeling the resin transfer molding manufacturing process has been developed at the U.S. Army Research Laboratory. This environment utilizes an implicit numerical method for modeling resin flow, a thermal model for analyzing convection and conduction, and a resin kinetics model to compute the heat generated and degree of resin cure during the curing process. The computing environment also includes a multiscale thermal residual stress model for computing the distortions and residual stresses in the composite component caused by the manufacturing process. All of these models have been tied together within a parallel object-oriented programming framework. This paper will discuss the computing environment in detail and its utility to real world applications. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Although deformation features of ECAP have been widely studied and investigated through numerical approaches, experimental observations are very scarce in the literature. Therefore, in this paper, quasi-3D strains in multi-sectioned samples during one pass of ECAP are analyzed, for different friction conditions and material properties. From this study, it can be concluded that ECAP is a plane-strain process and friction and material properties affect the strain distribution, strain homogeneity and also the work-piece geometry. Furthermore, ECAP can be interpreted as a combination of shear and stretch. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

Homogenization theory has been well accepted by the applied mechanics modeling community for its ability to integrate small-scale microstructure phenomena into bulk continuum equations using convergent features of asymptotics. This paper describes an extension of the method to handle asymptotically small atomic scale systems at zero temperature embedded within a deforming continuum. A so-called inner displacement naturally arises in the formulation that enables the consideration of distributed anharmonic crystalline effects that would otherwise be unapproachable with bulk continuum methods alone. The result is a simple computational mechanics method that, first, maps instantaneous continuum deformation gradients to deforming defected crystalline arrangements then, second, provides convergent effective material properties to be used for consistent continuum calculations. The intended applications are those involving patterned defects, either in bulk or on surfaces, which allude to possible manufacturing scenarios. Simple 2-D examples are shown for in-plane deformation of graphene possessing various types of point defects. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

With advances in computer capabilities, cost of sheet metal forming has being reducing mainly due to the reduction of trial and error approaches. At the moment, a complete process can be simulated on computer and appropriate forming conditions optimized before actual industrial forming process is carried out. While formability predictions have improved, the problem of springback exhibited by most metal, including aluminum alloy AA6111-T4, after forming persist and often leads to significant part fit-up problems during assembly. There are a number of factors that affect springback and perhaps the most significant one is constitutive equation. In this paper springback predicted by six advanced kinematic models are evaluated. In addition an improved constitutive kinematic model is presented. It is shown that by adding stress correction term (SCT) to Armstrong-Frederick model a relatively simple and yet accurate stress prediction could be obtained. The SCT was developed with the assumption that the yield surface remains convex, yield center depends on translation, size and shape variations of the yield surface. The model is implemented in a commercial finite element code (ABAQUS/Standard) via its user material interface (UMAT). Numerical simulations of U-bending were performed using automotive aluminum sheet material (AA6111-T4). It was noted that springback has inverse relationship with residual stress. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

In this paper, we propose a multi-time scale modeling technique for analyzing cyclic plastic deformation in crystalline solids subject to periodic loading. An asymptotic expansion of the variables in the time domain, together with homogenization forms the basis of multi-time scaling. In the macroscopic scale analysis, the oscillatory behavior of the load is averaged out and neglected, and the rate of averaged material behavior is quite slow in cyclic deformation. Implicitly, this means that the periodicity of some variables may be assumed for the oscillatory potion of the material behavior may be approximated. In this formulation, the governing equations are divided into two initial-boundary value problems with two different time scale: one is long time scale problem for describing the smooth averaged solution (global problem) and the other is for the remaining oscillatory potion (local problem). For the global problem, long time increments, which are longer than one cycle period, can be used and this multi-time scaling becomes an effective integrator. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

In this paper, we propose a multi-time scale modeling technique for analyzing cyclic plastic deformation in crystalline solids subject to periodic loading. An asymptotic expansion of the variables in the time domain, together with homogenization forms the basis of multi-time scaling. In the macroscopic scale analysis, the oscillatory behavior of the load is averaged out and neglected, and the rate of averaged material behavior is quite slow in cyclic deformation. Implicitly, this means that the periodicity of some variables may be assumed for the oscillatory potion of the material behavior may be approximated. In this formulation, the governing equations are divided into two initial-boundary value problems with two different time scale: one is long time scale problem for describing the smooth averaged solution (global problem) and the other is for the remaining oscillatory potion (local problem). For the global problem, long time increments, which are longer than one cycle period, can be used and this multi-time scaling becomes an effective integrator. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

New production technologies have been developed in these last few years as answers to new market needs such as high production flexibility, low volume batches, more complex shapes of the final pieces and new materials. In particular, for sheet forming the new developed technologies are flexible forming, sheet die-less forming and sheet fluid forming. In previous works the authors have already described the results obtained studying a new sheet forming process based on general purpose CNC machine (called sheet incremental forming on CNC machines) equipped with special tool. This kind of process can be used to produce prototypes of industrial components and also for low volume batches. The present paper reports the results of the analysis conducted on the produced pieces in terms of metallographic structure, hardness distribution and breaking conditions. These results are very interesting in order to understand the physical limits of the material when subjected to this peculiar deformation process. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

In sheet forming, the creation of wrinkles in the flange area of the blank commonly occurs. When diaphragm forming aligned-fiber-reinforced thermoplastic composites, observations reveal that the wrinkles tend to occur at angles oriented at forty-five degrees to the axis of the fibers. Intuition suggests that this is related to shear, but this may be misleading. The results of a stress-analysis and buckling analysis of this flange wrinkling problem are discussed. The forming of the thermoplastic sheets occurs at elevated temperatures and the sheet is essentially inextensible in the fiber direction. This leads to high anisotropy ratios of in-plane stiffness properties. The out-of-plane bending of the sheet will be strongly influenced by the presence of polymeric diaphragms. To investigate the buckling problem for this forming situation, a finite-difference formulation was developed. The solution revealed that only when one considers the combined effect of the thermoplastic composite and the polymeric diaphragms does the analysis predict the observed forty-five degree buckles. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]