Elastic Deformation Limit Research Articles

Identification of contact parameters from elastic-plastic impact of hard sphere and elastic half space

The theoretical and experimental analysis described in this paper demonstrate a simple systematic procedure to determine the contact parameters between a spherical impactor and an elastic half space via impact tests. Two main contact parameters were measured at different velocities of impact, that is the time duration of contact and the maximum normal contact force. A general nonlinear contact model based on power law is used to extract the contact stiffness and frequency of contact resonance from these two main contact parameters. Experimental results were obtained and compared for three steel samples with different hardness numbers and impacted by different sphere diameters of 2.0, 2.5 and 3.5mm to investigate the limits of elastic deformation. Effect of the used sphere diameter on the contact parameters are shown. The test results show that the adopted model using independently measured material data can predict the contact parameters due to hard sphere impact with elastic half space. The general trend shows the increase of contact stiffness with the sphere diameter but the limits of elastic regime decrease.

Strong Hall-Petch Type Behavior in the Elastic Strain Limit of Nanotwinned Gold Nanowires.

Pushing the limits of elastic deformation in nanowires subjected to stress is important for the design and performance of nanoscale devices from elastic strain engineering. Particularly, introducing nanoscale twins has proved effective in rising the tensile strength of metals. However, attaining ideal elastic strains in nanotwinned materials remains challenging, because nonuniform twin sizes locally affect the yielding behavior. Here, using in situ high-resolution transmission electron microscopy tensile testing of nanotwinned [111]-oriented gold nanowires, we report direct lattice-strain measurements that demonstrate a strong Hall-Petch type relationship in the elastic strain limit up to 5.3%, or near the ideal theoretical limit, as the twin size is decreased below 3 nm. It is found that the largest twin in nanowires with irregular twin sizes controls the slip nucleation and yielding processes in pure tension, which is in agreement with earlier atomistic simulations. Continuous hardening behavior without loss of strength or softening is observed in nanotwinned single-crystalline gold nanowires, which differs from the behaviors of bulk nanocrystalline and nanotwinned-nanocrystalline metals. These findings are of practical value for the use of nanotwinned metallic and semiconductor nanowires in strain-engineered functional microdevices.

Analysis of residual stress relief mechanisms in post-weld heat treatment

This paper presents a recent study on weld residual stress relief mechanisms associated with furnace-based uniform post-weld heat treatment (PWHT). Both finite element and analytical methods are used to quantitatively examine how plastic deformation and creep relaxation contribute to residual stress relief process at different stages of PWHT process. The key contribution of this work to an improved understanding of furnace based uniform PWHT can be summarized as follows:(1)Plastic deformation induced stress relief during PWHT can be analytically expressed by the change in material elastic deformation capacity (or elastic deformation limit) measured in terms of material yield strength to Young's modulus ratio, which has a rather limited role in overall residual stress relief during furnace based uniform PWHT.(2)The most dominant stress relief mechanism is creep strain induced stress relaxation, as expected. However, a rapid creep strain development accompanied by a rapid residual stress reduction during heating stage before reaching PWHT temperature is shown to contribute to most of the stress relief seen in overall PWHT process, suggesting PWHT hold time can be significantly reduced as far as residual stress relief is concerned.(3)A simple engineering scheme for estimating residual stress reduction is proposed based on this study by relating material type, PWHT temperature, and component wall thickness.

Воздействие жесткого элемента на свободную поверхность упругого материала

The paper presents an example of the simplest mathematical techniques to determine the maximum deformation of the free surface of an elastic body in contact with the non-deformable element. Considerable attention is given to the calculation in the position of a free surface. Since the model operates with an incompressible elastic medium, the displacement components completely satisfy the Laplace equation , for which the maximum principle holds , which is that the maximum (limit ) on the boundary deformation are achieved on the free surface , although the stresses on this site are minimal. This problem is important in the study of the processes of deformation of the contact surfaces of elements of different mechanisms , where the question of determining the limit of elastic deformation is structurally important.<br /> material , mathematical modeling, potential displacement , iterative- difference technique .

Physicochemical properties of culms in rye (Secale cereale L.) with a brittle stem

In carrying out a genetic analysis of rye in terms of a “brittle stem” trait, sister plants with normal and brittle stems were obtained. The culms of plants were studied in terms of chemical composition, spectroscopic parameters, and mechanical strength. Differences among plants with different types of culm were found in terms of a number of indicators, such as the content of aromatic monomers of lignin and the ratio of different types of chemical bonds. Culms of normal and brittle rye of the same diameter vary in terms of an elastic modulus and elastic deformation limit. It was found that stems of mutant plants are destroyed under lateral stress by means of the fragile fracture mechanism, while those in normal plants are destroyed by ductile fracture. The limits of elastic deformation and strength are significantly higher for normal plants. By nuclear magnetic resonance methods, we detected differences in the chemical structure of lignins in terms of the following: the content of aldehyde and methoxyl groups, total aromaticity, and the number of ordinary ether bonds, by which lignin units are associated with polysaccharide fragments of cellular walls. Higher lignin content in a mutant does not increase the mechanical strength of the culm. On the contrary, there is a decrease in the limits of elastic deformation and an increase in the fragility of the shoots. Probably, the mutation bs, except for direct action (brittleness of the culm), causes an imbalance of metabolic processes in the formation of secondary cell walls and leads to deviations from the optimal ratio of carbohydrate and lignin components. The differences found in various indicators can be used in breeding research associated with important economic traits of cereal stems.

Control of rock jacking considering spread of grout and grouting pressure

This paper describes a theoretical approach for monitoring fracture dilatancy (or “jacking”) during grouting. From this, a methodology to optimize the grout pumping pressure has been developed, based on the required penetration length (i.e. the distance that the grout spreads from the grout hole into the network of fractures within the rock mass). Empirical rules are put forward to prevent the damage that may result from uncontrolled deformation (Jacking) of the fractures, by limiting either pumping pressure or the injected grout volume, or by a combination of both. The state of the fractures and the spread of the grout when these limits are reached are discussed. The theoretical approach, which is referred to here as the Real Time Grouting Control Method, enables the estimation of grout penetration length or “spread” in real time. This gives an opportunity to monitor fracture dilation as it happens and, for the purpose of this paper, the allowable limits of elastic deformation and jacking have been estimated based on the grout spread. Two case histories are analyzed, for which the physical reaction of the fracture deformation with time and grout spread are determined from the recorded pressure and flow. By comparing the observed physical reaction with the theories for jacking presented here, the Real Time Grouting Control Method has been validated, and it is shown that this theoretical approach is superior to commonly used empirical methods, in that it allows the optimization of the pumping pressure to achieve a given penetration length in the shortest time and with an acceptable fracture dilatancy. This approach is a major step forward in customizing grouting works.

Strain-Induced Large Exciton Energy Shifts in Buckled CdS Nanowires

Strain engineering can be utilized to tune the fundamental properties of semiconductor materials for applications in advanced electronic and photonic devices. Recently, the effects of large strain on the properties of nanostructures are being intensely investigated to further expand our insights into the physics and applications of such materials. In this Letter, we present results on controllable buckled cadmium-sulfide (CdS) optical nanowires (NWs), which show extremely large energy bandgap tuning by >250 meV with applied strains within the elastic deformation limit. Polarization and spatially resolved optical measurements reveal characteristics related to both compressive and tensile regimes, while microreflectance spectroscopy clearly demonstrates the effect of strain on the different types of excitons in CdS. Our results may enable strained NWs-based optoelectronic devices with tunable optical responses.

Fabrication and electromechanical characterization of near-field electrospun composite fibers

We report the use of near-field electrospinning (NFES) as a route to fabricate composite electrodes. Electrodes made of composite fibers of multi-walled carbon nanotubes in polyethylene oxide (PEO) are formed via liquid deposition, with precise control over their configuration. The electromechanical properties of free-standing fibers and fibers deposited on elastic substrates are studied in detail. In particular, we examine the elastic deformation limit of the resulting free-standing fibers and find, similarly to bulk PEO composites, that the plastic deformation onset is below 2% of tensile strain. In comparison, the apparent deformation limit is much improved when the fibers are integrated onto a stretchable, elastic substrate. It is hoped that the NFES fabrication protocol presented here can provide a platform to direct-write polymeric electrodes, and to integrate both stiff and soft electrodes onto a variety of polymeric substrates.

Indentation of Foam-Based Polymer Composite Sandwich Beams and Panels Under Static Loading

Foam core composite sandwich structures are highly susceptible to damage when subjected to localized loading. Therefore, thorough study of the role of factors such as face sheet thickness, indentor diameter value, and crosshead displacement rate in indentation events is important. The objective of the present work is to investigate experimentally and numerically the influence of these factors on the nonlinear static indentation behavior of sandwich beams and panels consisting of glass fiber/resin face sheets and PVC (polyvinylchloride) foam core. Static indentation tests are carried out on sandwich composite beam and panel specimens using steel cylindrical and spherical indentors, respectively. Numerical models are developed for simulating the mechanical response of sandwich structures subjected to localized indentation beyond the limit of elastic deformation in the foam core. In this relation, the *CRUSHABLE FOAM and the *CRUSHABLE FOAM HARDENING options in the ABAQUS finite element program system are used. The numerical analysis results demonstrate good agreement with experimental data. It is found that increasing the face sheet thickness and indentor diameter value leads to increase in the load (for a given displacement). It is shown also that the indentation behavior does not exhibit sensitivity to crosshead displacement rate over the conditions considered in the present work.

Computer experiment on deformation of nanocrystals of the chromium-niobium system. Part 1. Atomic-structural rearrangements

Molecular-dynamic simulation of the process of stretching of chromium and niobium nanocrystals and chromium-niobium bicrystals was performed to a pair-potential approximation. Atomic mechanism of deformation and fracture is illustrated, which depends on the crystal orientation with respect to the acting force \(\bar P\). In the case of the initial orientation (100)⊥\(\bar P\), the reorientation mechanism (100)⊥\(\vec P\)→ (110)⊥\(\vec P\) is in action. In a bicrystal, it is niobium that deforms first and then the relay-race transfer of deformation from Nb to Cr takes place. With the initial configuration (110)⊥\(\vec P\), the fragmentation of the crystal and grain-boundary rearrangements are observed. Niobium crystallite in a bicrystal deforms only within the limits of elastic deformation whereas the deformation of chromium is of brittle-ductile mode. With the initial configuration (111)⊥\(\vec P\), the mechanism of pure brittle fracture is observed. In all cases, fracture of a bicrystal occurs along the interphase boundary. The causes of such atomic-structural transformations are explained.

Simulation of a fully coupled thermo–hydro–mechanical system in freezing and thawing rock

Abstract This paper describes the application of a numerical model of thermal–mechanical–fluid flow coupling system to the simulation of laboratory freezing and thawing experiments on rocks. A theoretical formulation that accommodates a linear stress–strain constitutive relationship is presented and a two-dimensional (plane stress) numerical modeling is performed based on the finite element method applied to thermo–poro–elasticity. As the primary objective of this research is to simulate the freezing and thawing process, the developed code takes into account the phase change of pore water during freezing. It is found from the numerical simulation that a relatively good prediction can be made of temperature transfer and deformation behavior within the elastic deformation limit. In some cases, however, large deformation results from the freezing processes, leading to material failure. Future research should therefore take into account irreversible and plastic effects.

Estimation of the stress state inside metals using stress perturbing waves and probe waves

A new method to detect the stress conditions inside metals such as the limiting stress value of elastic deformation is proposed. It is based on the nonlinear dependence of ultrasound velocity on stress. First, the nonlinear dependence of sound velocity on stress is observed in an Al alloy. Then equipment which consists of a wave generator for electromagnetic monopole stress perturbing pumping and a 50 MHz ultrasonic sound velocity change detecting unit is presented. In this system the stress perturbation is applied at the desired measuring region in the metal along with the probe wave and changes in the wave are observed. Finally, it is applied for the estimation of the elastic deformation limit of Al alloy and the usefulness of the method is confirmed.

Closure of rock joints

Previously we verified experimentally that a generalized form of the Greenwood‐Williamson theory describing the elastic contact of two random surfaces adequately predicts the closure of joints in fused silica glass samples. Here we present a similar analysis for experiments on rock. We have tested the theory quantitatively by comparing joint closure from experiment with joint closure predicted by the theory. These comparisons were made using topography data from the surfaces of the joints used in the closure experiments. Three types of tests were done: (1) Granite and quartzite samples were studied where the joints consisted of surfaces ground with #80 and #60 grits. Here the surfaces were random and uncorrelated with each other. These experiments permitted a direct test of the theory. As with the experiments on glass, the theory agrees with experiment. However, uncertainty in the values of the elastic constants for rock result in larger possible errors in predicting joint closure. (2) Tension fractures in granite and quartzite samples were studied. Here the surfaces were highly correlated with each other. The amount of closure expected for correlated surfaces depends on the degree of correlation, since this determines the effective roughness of the joint. Here the surface topography was repeatedly high‐pass filtered and the theory compared with experiment at each stage to determine the effective scale over which the surfaces were mismatched. (3) Ground surfaces of marble were subjected to the same loading conditions. Here the elastic assumption was no longer appropriate. These experiments are an example that the limit of elastic deformation is reached for all materials for surface asperities below a given dimension. This dimension is related to the indentation hardness of the material, which is lower for calcite than for silicate minerals.

A twin shear beam model for double chord RHS joints

A finite element elasto-plastic analysis of a twin shear beam model, developed to shed light on the behavior of separated double chord gap joints of rectangular hollow sections (RHS), is presented. The model treats a single beam member as composed of a plate simulating its inner web and a channel representing top and bottom flanges and the outer web. The twelve degrees of freedom (DOF) nonconforming plate bending element and the eight DOF plane stress elements are used to form a plate element for the inner web, while the channel consists of a grillage of beam elements. The analysis, extended beyond the elastic limit, accounts for strain hardening and material nonlinearity. A comparison of theoretical predictions with the experimental results of 24 specimens shows generally good agreement. The mean ratios of theoretical to experimental values are 0.97 and 0.87 for elastic stiffness and carrying capacity measured at a post elastic deformation limit.

Deformation of depleted uranium - 0.78 Ti under shock compression to 11.0 GPa at room temperature

The present work on depleted uranium alloyed with 0.78% titanium by weight (i.e., U-0.8 Ti) describes the nature of deformation it undergoes when subjected to shock compression at room temperature. The principal results emerging out of the present work are: (1) The stress limits of elastic deformation are dependent on the thickness of U-0.8Ti. The stress limit decreases from over 3.0 GPa at the impact surface to 1.2 GPa at a depth of 9 mm in U-0.8 Ti; (2) The lower limit of the stress agrees with the static yield stress in U-0.8 Ti; (3) Above the elastic stress limit, the deformation of U-0.8 Ti proceeds in a manner of the ideal plastic solid; and (4) The pressure derivative of Lame’s parameter of U-0.8 Ti is estimated to be 3.8.

The limit of elastic deformation in the contact of rough surfaces

The limit of elastic deformation in the contact of rough surfaces

Optical And Mechanical Properties Of Soda Lime Glass Under Shock Compression And Release

Previous results of plane shock wave experiments on soda lime glass do not show a sharp unambiguous cusp in its wave profiles indicating the limit of elastic deformation i.e., Hugoniot Elastic Limit (HEL). This research was initiated to determine whether the effect of the change in the refractive index of the glass on the shift in Doppler frequency can be used to determine its HEL under shock compression. Based on the results of a limited number of experiments performed on soda lime glass, it is inferred that the HEL of soda lime glass is 3.10 ± 0.06 GPa.

Normal Mode Bends for Circular Electric Waves

In dielectric-coated round waveguide the degeneracy or equality of phase constants of TE 01 and TM 11 waves is removed. In such a non-degenerate waveguide, mode conversion in bends can be reduced by changing the curvature gradually instead of abruptly. With curvature tapers, which are of the order of, or longer than, the largest beat wavelength between TE 01 and any of the coupled waves, propagation of only one normal mode is maintained throughout the bend. Linear curvature tapers can easily be made by bending the pipe within the limit of elastic deformation. Changes in the direction of a waveguide line can thus be made by inserting a dielectric-coated guide section which is elastically bent over a fixed center point. A thirty degree change of direction of a 2-inch I.D. pipe with 30 ft of a dielectric-coated guide yields a total bend loss at 5.4-mm wavelength that is twice the TE 01 loss in 30 ft of straight pipe. An optimum bend geometry is found which minimizes the total bend loss. The normal mode bend is a broadband device

The Rheological Curve

THE shear of a non-Newtonian body, that is, a plastic material or a high-polymeric pseudo-fluid, follows a mechanism showing analogy to that of a true fluid as expressed by the Maxwell equation; but whereas the relaxation of true fluids is purely time-dependent, in the case of non-Newtonian bodies a critical angle of tangential deformation characteristic for each material marks a threshold limit of elastic deformation before relaxation sets in. This elastic limit in plastic materials corresponds to the separation of a secondary aggregate into primary particles and, in the case of pseudo-fluids, to the inception of unkinking of the polymer molecules.