Tensile Stress-strain Diagram Research Articles

Hydrogen degradation of steels in gas mains after long periods of operation

We study the degradation of the mechanical and corrosion properties of 17G1S steel in gas mains as a result of operation for 28–40 yr. We reveal the simultaneous decrease in its strength and hardness, on the one hand, and impact toughness and crack resistance, on the other hand. The indicated parameters prove to be most sensitive to the in-service degradation of the metal. The degradation of steel leads to the increase in the strain-hardening coefficient and the appearance of the yield plateau in the tensile stress-strain diagram and causes the appearance of sensitivity to hydrogen embrittlement increasing in the process of operation. We analyze the role of absorbed hydrogen affecting the mechanism of strain aging and responsible for the appearance of defects. It is shown that the polarization resistance can be used not only for monitoring of the corrosion state of gas pipelines but also for the prediction of changes in their mechanical properties in the process of operation.

On the calculation of deformation curves for two-phase cermets

Analytical algorithms for the construction of tensile and compression stress-strain diagrams of two-phase cermets are proposed, which are based on the concept of mean stresses in the phase volume and physical equations of the theory of small elastoplastic strains. The deformation properties and strength of cermet are supposed to depend on such parameters of its microstructure as mean size and coefficient of variation of solid phase grain-size distribution, contiguity coefficient of solid phase grains, and mean thickness of the metal phase inter-layers. A numerical analysis of the characteristic parameters of deformation curves for WC-Co hard metals has been carried out over a wide range of cobalt concentration and carbide grain size. A good agreement between the theoretical values of ultimate tensile and compression strength and known experimental values has been established. The constructed model deformation curves for hard metals may be regarded as alternatives to the corresponding experimental curves of stress against relative change in specimen length.

A nanocomposite based on a styrene-acrylate copolymer and native montmorillonite clay 1. Preparation, testing, and properties

The preparation of a polymer nanocomposite by compounding an aqueous polymer emulsion with an aqueous dispersion of montmorillonite clay is described. A styrene-acrylate copolymer emulsion and a purified native montmorillonite clay from Latvian deposits are used. An X-ray diffraction analysis and differential scanning calorimetric thermograms are shown. Data on the influence of montmorillonite concentration on the tensile stress-strain diagram, elasticity, yield stress, breaking stress, and ultimate elongation of the processed nanocomposite material are obtained.

Mechanical Properties of Blends of Low-Density Polyethylene with Chlorinated Polyethylene

The results of experimental investigation into the mechanical properties of blends of low-density polyethylene (LDPE) with chlorinated polyethylene (CPE) in tension are presented. The specimens of pure LDPE, CPE, and nine types of LDPE/CPE blends, with different content of components at 10 wt.% intervals, were examined. Data on the influence of blend composition on the tensile stress-strain diagram, elastic modulus, yield stress, breaking stress, and ultimate elongation are obtained. The results of investigations of creep are also reported. It is found that the creep compliance (the total current compliance minus the elastic compliance) obeys the power law of creep.

Molecular Dynamics Study of the Destruction of Single-Walled Carbon Nanotubes under Tension

The deformation and destruction of single-walled open carbon nanotubes are investigated in the framework of the molecular dynamics model of charges localized at bonds, which takes into account the atomic (ionic) and electronic degrees of freedom. This approach allows one to study excited electronic states induced by electronic transitions and to investigate both the ionic and electronic subsystems simultaneously. The structural transformations of nanotubes with (10, 2) chirality under tension are investigated, and the tensile stress-strain diagrams of these nanotubes in the temperature range 100–1000 K are calculated. It is established that, at low and moderate temperatures, the destruction of the nanotubes has a similar nature: the interatomic covalent bonds are broken in the normal cross section of the nanotube. At high temperatures, the nanotube undergoes a scission along the stretching axis.

Influence of alloying and impurity element contents on V–Ti–Cr alloy properties

This work presents the results of a property study and analysis of V–Ti–Cr alloys with a total base component concentration of Ti + Cr in the range of 8–30% with consideration of the influence of impurity and possible transmutation elements. The effect of the base alloying elements (titanium, chromium) and impurity elements (iron, silicon, aluminum, scandium etc.) on the recrystallization temperature, hardness and mechanical properties of alloys at different temperatures has been estimated. The role of dynamic strain aging with respect to the increase of vanadium alloy strength and intermittence developed on a tensile stress–strain diagram at temperatures above 400 °C has been shown.

Effect of Cyclic Loading on Crack Tip Opening Displacement in AMg6 Alloy

We study the effect of cyclic loading whose amplitude is close to the threshold stress intensity factor on the static tensile stress-strain diagram and creep of cracked specimens of AMg6 alloy and analyze the influence of the frequency and range of the stress intensity factor on the crack-tip opening displacement caused by creep.

The Strength of Bolted and Bonded Single-Lapped Composite Joints in Tension

This work is primarily concerned with a failure analysis of single-lapped bolted and bonded mixed-composite joints, representing practical situations, both in terms of experimental data and theoretical appreciation. Two kinds of stacking sequences in adherends are tested: quasi-isotropic and cross-ply. The adhesives include thermal-setting and thermal-plastic types. The bolts used to clamp the bonded joints are made of 304 stainless steel, whilst the rivets are of NAS 1919 C05 according to National Aerospace Standards. The important invented techniques in making riveted and bolted joints and measuring their respective clamping pressure are disclosed, and the main contribution of systematic experimental data in contrast with numerical prediction is highlighted as follows. The bolting arrangements can be divided into one (1 x 1), three (1 x 3, 3 x 1), six (2 x 3) and nine (3 x 3) configurations. The empirical results indicate that the joint of six (2 x 3) bolts possess the highest strength, nine (3 x 3) bolts the second strongest, followed by (1 x 3), (3 x 1); while the one bolt geometry is the weakest. The mixed joints with more than three bolts will fail by adhesive delamination and tension failure in adherends transversely. However, the failure mechanism for the one bolt system is different, in that delamination occurs first, then bolt bending and shearing, and finally a tension-type failure. A typical tensile stress-strain diagram is linear before delamination. We also adopt the C-scan non-destructive testing (NDT) technique to examine damage initiation sites and to compare this information with the numerical prediction obtained using the finite element method. The comparison is satisfactory. Finally, the joint strength increases with increasing overlap length, until the strength approaches asymptotically a constant value for longer overlap lengths.

Dynamics of uniaxial tension of a viscoelastic strain-hardening body in a system with one degree of freedom. Part 1. Prescribed motion

The behavior of an open mechanical dissipative system formed by a viscoelastic hardening body and an elastic working element used for the energy transfer between the testing machine and the deformed body is described by a third-order dynamic differential equation with controlling parameters that depend on the reduced mass and stiffness of the system, its viscous resistance, the degree of strain hardening, the type of the stressed state of the body, and the dissipation of energy in a viscous ambient medium. We analyze the dynamics of uniaxial tension of the deformed body below and above its elasticity limit for the case where the forces induced in the process of motion are determined by the kinematics of the testing machine with prescribed motion. We establish the dynamic nature of the nonlinear section of the tensile stress-strain diagram beyond the elasticity limit of the viscoelastic body corresponding to the so-called “nonlinear elasticity”. It is shown that the appearance of this section is connected with a transient relaxation process. Upon the termination of this process, the forces acting in the system are determined by the viscous flow of the body corresponding to its yield limit. Above the elasticity limit of the body, we observe the formation of a bistable state of the system caused by changes in the controlling parameters and lag effects and leading to its macroscopic acoustic activity.

Three-stage model of an elastoplastic cracked body

We propose a three-stage model of an elastoplastic cracked body, which takes into account the evolution of stresses in the prefracture zone according to the complete tensile stress-strain diagram of the investigated material. The zone of loosening corresponding to the last (descending) part of the tensile stressstrain diagram lies in the immediate vicinity of the crack tip. The zone of plastic deformation of the material is located after the zone of loosening. These zones are simulated by separate rectilinear stress-strain diagrams taking into account the effect of linear hardening of the material. Within the framework of the proposed model, we formulate a deformational fracture criterion and determine the characteristics of crack resistance of D16T steel.

Generalized model of an elastoplastic cracked body

We propose a generalized model of an elastoplastic cracked body which takes into account not only the zone of plastic yield but also the prefracture zone (the final descending section of the complete tensile stress-strain diagram) and formulate a strain criterion of limiting equilibrium based on the use of the following characteristics of the material: the maximum level of stresses in the plastic zone σ0, the critical crack tip opening displacement δc, and the critical sizes of the prefracture zoneds and the zone of plastic yielddnc. The parameters σ0 and δc are measured experimentally, whileds anddnc are determined from the criterional equations. We also consider the case of a brittle body (the zone of plastic yield is absent) and present the characteristics of crack-growth resistance of D16T alloy found within the framework of the proposed model.

Study of the true tensile stress-strain diagram of plain concrete with real size aggregate ; need for and design of a large Hopkinson bar bundle

L'idee est discutee d'employer deux grands faisceaux de barres d'Hopkinson, disposees de facon speculaire, pour l'observation de la distribution instantanee de la contrainte et de la deformation sur la section resistante des grandes eprouvettes de beton, chargees en dynamique rapide

A tensile stress-strain diagram of steel 40KhN after a surface temper

A tensile stress-strain diagram of steel 40KhN after a surface temper

Establishment of Dynamic Failure Model and Examination on Dynamic Failure Process

The present paper proposes a new dynamic failure process simulation model considering the effect of matrix shear failure as well as random fiber breaks based on a shear-lag theory in which an additional time variable is also incorporated by taking the mass of fiber and matrix elements into account. An exact time-dependent stress redistribution process in a composite failure model is evaluated by means of a finite difference scheme based on an increment method for unidirectional carbon (C) and carbon (C) /glass (G) hybrid FRP models.It is observed that the time-dependent stress concentration factor evaluated by the simulation is in good accordance with the Hedgepeth's analytical solution. It is also clarified that the stress in carbon fiber is relieved to some extent due to the presence of neighbouring glass fibers in hybrid C/G hybrid FRP models.The stress wave propagation is successfully simulated by visualizing a time-dependent change in nodal displacements as well as pursuing a dynamic failure process of a composite failure model. These simulations are shown to be effective in characterizing different failure processes and stress wave propagation behaviors of unidirectional CFRP under varied higher strain rates.Finally, a simple damping term is taken into account in the dynamic failure process simulations. It is shown that a clear difference exists in the dynamic failure process and the resulting tensile stress-strain diagram of CFRP and C/G hybrid FRP under varied higher strain rates.

Concentration dependence of the deformation characteristics of high-density polyethylene compositions with dispersed fillers

costs. There has recently been a trend toward the production of polypropylene- and polyethylene-bas ed materials containing up to 50% filler by weight [1]. These materials have enhanced stiffness and the savings in polymer may be as much as 30% by volume. At the same time, the deformatLon characteristics are consLderably reduced. There is a fall in the relative elongations at the yield point and at break and hence a decrease in impact resistance, in order to clarify the reasons for these changes and determine the possibility of mainta[ning technically important characteristics at an acceptable level, it is necessary to make a systematic study of the phys icomechanfcal properties over a broad interval of filler concentrations. Our task was to study the dependence of the deformation characteristics on the filler content under conditions favoring the development of maximum tens ile strains. In preparing the specimens we used high-density polyethylene (HDPE) powder, grade 20908-040, containing 0.5% Erganox by weight. As the fiUer we chose calcLte {natural calcium carbonate}. After grinding, the mean filler particle size was 5 pro, and the content of particles more than 10 ~m Ln size did not exceed 10%fl The HDPE and the calcLte were dried to a residual moisture content of not more than 0.1%. The powders were mixed, first in a high-speed mixer and then in the melt at a temperature of 170-180~ in the chamber of a laboratory rotary mixer. The amount of filler in the mixture was checked by thermogravimetri c analysis. The test specimens were out out of sheets 1.3-1.4 mm thick, pressed at 180~ and a pressure of 80 atrn. in individual tests we used specimens injection-molded under the conditions recommended in [2]. The tensile stress-strain diagrams were recorded on an [nstron-l195 tens ile testing machLne at room temperature and at a strain rate of 0.15 rain -i. To a considerable extent the mechanical properties of the compositions are determLned by the compos lt ion and amount of the modifiers added. The choice of effective modifiers for polyoleflns, and In partLcular HDPE, is a subject of research [1], but at present there are no proven recommendatLons as regards controllLng the interracial bond. A comparison of the properties of compos Ltions with different modifiers has shown that salts of fatty acids have the greatest effect in improving the deformation characteristics. Table 1 compares the properties of compositions with and without 2% zLnc stearate added to the filler, rntroducing the stearate leads to a reduction in the stresses and a considerable increase Ln relative elongation. At a high filler content a sharp increase in the fluidity of the melt Ls also observed. These changes are a consequence of the Lmprovement in dispersibility and the weakening of the interracial bond. Accordingly, all the compositions contained zinc stearate.

Critical current behavior in bending and tensile stressed Nb<inf>3</inf>Sn composites at temperatures below 4.2 K

Critical current measurements were obtained on bronze-diffused reacted Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn multifilamentary conductors as a function of mechanical stress loads and applied transverse magnet fields up to 13 T for temperatures in the range between 4.2 K and 1.9 K. To simulate the winding handling of reacted Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn wires for superconducting magnets, operated in normal or superfluid helium the effects of room temperature bend strain on current carrying capacities of monolithic and flat cable conductors were investigated by controlled winding processes using mandrels with various diameters. The results show a field-dependent degradation in critical current with increasing bend strain for both conductor types. Only a very small precompression effect (< 0.5%) on critical current is observed. At higher strain, beginning at 0.4%, the critical current decreased rapidly, reaching at 13 T by more than 50% at a bending strain of 0.9% calculated on overall conductor cross section. Both optical and scanning electron microscopy were used to examine the samples before and after testing. Additional data on the mechanical properties (tensile stress-strain diagrams) of Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn samples are presented, along with some preliminary critical current versus uniaxial tensile stress measurements at 2.2 K and 4.2 K, respectively. First results indicate that the increase in critical current at 2.2 K is relatively larger (about 25%) than that at 4.2 K. This fact is interesting for Nb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> Sn magnets cooled with superfluid helium to obtain a broad strain tolerance.

Tension Stiffening in Reinforced Concrete Slabs

A nonlinear finite element model is used to predict the short-term behavior of reinforced concrete slabs under transverse service loads. The model is based on small deflection plate bending theory and uses a layered 16-degree-of-freedom rectangular plate bending element. The sources of material nonlinearity in reinforced concrete slabs are examined and accounted for in an incremental nonlinear solution procedure. Various methods are considered for treating the tension stiffening effect that occurs between the cracks in the tensile concrete in regions close to the reinforcement. Numerical calculations are used to assess the relative merits of these methods and to test the validity of the model. A simple treatment of the tension stiffening effect is proposed in which a modification is made to the tensile stress-strain diagram for the reinforcing steel. This produces accurate results with relatively economic use of computer time.

Tensile behavior of plastic foams

The tensile stress-strain diagram of plastic foams is calculated on the basis of a previously proposed 14-faced cell model. An S-shaped inflection due to the flexural deformations of the ties is detected on the initial section of the diagram. It is shown that for closed-celled foams this inflection may degenerate. The results of testing PVC and polyurethane foams (volume content of polymer base about 3–6%) prove to be in satisfactory agreement with the calculations.

Strength of Thick-Walled Cylindrical Pressure Vessels

This paper gives a critical review of the various theories for predicting the maximum pressure that have been applied to thick-walled cylindrical pressure vessels. A new anisotropic theory proposed by the authors is also reviewed, and all the available experimental results are compared with this and other theories. Based upon agreement with test results and relative simplicity of application, the method developed by the authors is recommended. In recommending the proposed theory, it should be noted that the study is restricted to materials with instability loads, as characterized by a horizontal slope in the tensile nominal stress-strain diagram.

Deformations of an elastic-plastic cylindrical shell with linear strain hardening

A thin- walled circular cylindrical shell of finite length is subjected to a slowly increasing uniform radial pressure. The tensile stress-strain diagram of the material of the shell consists of two straight-line segments, the first representing elastic behaviour and the second plastic. A certain simplified piecewise-linear yield function between the stress resultants in the shell is assumed, and the strain-hardening is taken to be isotropic. The stress-strain law is a flow-type law determined by the plastic potential. The complete solution to this problem is obtained directly from the governing equations. Various limiting cases are considered, including elastic perfectly plastic and rigid strain hardening. The results are applied to an example, and salient features are shown graphically.