Showing papers on "Stress–strain curve published in 1982"

Stress-strain behavior of concrete confined by overlapping hoops at low and high strain rates

Abstract: An experimental investigation into the behavior of short reinforced concrete columns is described. Twenty-five concrete units, each 450 mm (17.7 in.) square by 1200 mm (47.2 in.) high, containing either 8 or 12 longitudinal steel bars and different arrangements of square or octagonal steel hoops, were subjected to concentric or eccentric loads to failure at different strain rates. Results presented include an assessment of the effect of eccentricity of load, strain rate, amount and distribution of longitudinal steel, and amount and dis­ tribution of transverse steel. A stress-strain curve for concrete con­ fined by hoop reinforcement and loaded at a high strain rate (com­ parable with seismic loading) is proposed and compared with an existing curve based on previous tests conducted at low strain rates. The available ultimate compressive strain for concrete confined by hoop reinforcement is also discussed.

The mechanical properties of superplastic materials

Abstract: The relationship between stress and strain rate is often sigmoidal in superplastic materials, with a low strain rate sensitivity at low and high strain rates (regions I and III, respectively) and a high strain rate sensitivity at intermediate strain rates (region II) where the material exhibits optimal superplasticity This relationship is examined in detail, with reference both to the conflicting results reported for the Zn-22 pct Al eutectoid alloy and to the significance of the three regions of flow

Complete Triaxial Stress-Strain Curves for Concrete

Abstract: A method to predict the ascending and the descending parts of stress-strain curve of concrete subjected to triaxial compressive stresses is presented. The proposed analytical stress-strain relationship depends on the values of the three principal stresses and strains at the ultimate compressive strength. A criterion to predict the triaxial compressive strength is proposed, which is sensitive to all three stress invariants. To enable predictions of the post-peak stress-strain relation, experiments were conducted on concrete confined by steel tube. Concretes with different compressve strengths were confined by steel tubes of varying thicknesses. The predicted stress-strain curves compared favorably with the available experimental data on uniaxial, biaxial, and triaxial compression.

Finite Element Method (FEM) Calculations of Stress-Strain Behavior of Alpha-Beta Ti-Mn Alloys: Part I. Stress-Strain Relations

Abstract: By use of a NASTRAN18 Computer Program, the Finite Element Method (FEM) has been employed to calculate the effect of particle size, matrix, and volume fraction on the stress-strain relations of α-β titanium alloys. It was found that for a given volume fraction, the calculated stress-strain curve was higher for a finer particle size than for a coarse particle size within the range of the strains considered, and this behavior was seen for all the different volume fraction alloys considered. For a 50:50 vol pct α-β alloy, the stress-strain curve withβ, the stronger phase, as the matrix was higher than that with α, the softer phase, as the matrix. The calculated stress-strain curves for four different vol pct α alloys were compared with their corresponding experimental curves, and in general, good agreement was found. Whenever there were discrepancies, they were discussed by comparing the morphology of the mesh used in the calculations with the morphology of the actual materials.

Concrete under Impact Loading, Tensile Strength and Bond

Abstract: Uniaxial impact tensile tests on plain concrete were carried out with the aid of Split Hopkinson Bar equipment with stress rates of up to 60000 N/mm2. s. Various concrete mixes were investigated under. dry and wet conditions. All the concretes showed an increase in strength with increasing stress rate. At very high stress rates the strength may attain twice the static tensile strength. Repeated impact tensile loading reduces the strength considerably more than cyclic loading does with conventional stress rates. The bond between reinforcing steel and concrete was studied in pull-out tests with short embedment length. The results showed the bond strength and stiffness of deformed bars to increase with the loading rate, whereas plain bars and prestressing strands were hardly affected by the loading rate. It proved possible to formulate the tensile strength and the bond behaviour as a function of stress rate by means of a power function. Relations between compressive strength and tensile strength are given for various stress rates.

Constant strain- and stress-rate compressive strength of columnar-grained ice

Abstract: Unconfined compressive strength of transversely isotropic columnar-grained ice has been investigated for loads applied normal to the longitudinal axis of the columns at the high homologous temperature of 0.96 Tm (Tm is the melting temperature) under truly constant strain and stress rates. A closed-loop, servo-hydraulic test system inside a cold room was used. Both the strain- and stress-rate dependences of upper yield stress can be expressed in terms of power laws. The observed strain-rate dependence of strength was found to be numerically the same as the dependence of viscous-flow rate on stress in constant stress creep tests at the same temperature. It is shown that the strain-rate sensitivity of yield strength compares well with previous results (obtained under constant cross-head rates using a conventional machine) only if the average strain rate to yield is used as the independent variable instead of the conventional nominal strain rate. The paper also discusses the strain and time aspects of the tests. It shows interdependence among values for compressive yield strength, strain rate, failure strain and time very similar to the interdependence among the corresponding values in tensile creep failures in metals, alloys and other polycrystalline materials at high temperatures. It is emphasized that the splitting type of brittle-like premature failure depends on the stiffness of the test system and should not be considered to be a fundamental material property. The concept of failure modulus is proposed for examining the ductile to brittle transition.

Influence of Local Strain Distribution on Low-Cycle Fatigue Behavior of Thick-Walled Structures

Abstract: An optimum design of thick-walled components such as high-pressure vessels and reactor vessels requires knowledge of the local strain distribution, the strain/stress state, and the material's behavior under elastic-plastic deformations. The multiaxial strain-state is transformed into a uniaxial strain-state according to Von Mises's yield criterion. Fatigue experiments on planar and cylindrical specimens with high strain concentrations and biaxial strain-states prove that low-cycle material properties as determined from unnotched specimens can be applied for design based on a defined initial crack length. A design including the stage of crack-propagation can be practiced only in special cases; in general it can not be recommended because of very high strain intensities and the resulting small critical crack depths, as service experience shows. For the functional reliability of the component it is also important that the local structural yield point, which can be a multiple of the material's yield point, is not exceeded by maximum loading. When designing such structures prestrains resulting from manufacturing or overloading must also be considered. Tests carried out with prestrained specimens show that fatigue life is decreased with increased prestrain due to cyclic softening.

Elastic-plastic finite element analyses of short cracks

Abstract: Stress and strain distributions and crack opening displacement characteristics of short cracks have been studied in single edge notch bend and centre cracked panel specimens using elasticnplastic finite element analyses incorporating both a non strain hardening and a power law hardening behaviour. J contour integral solutions to describe stress strain conditions at crack tips for short cracks differ from those for long cracks. The analyses show that (i) short cracks can propagate at stress levels lower than those required for long cracks and (ii) a two-parameter description of crack tip fields is necessary for crack propagation.

Stress-strain analysis and the lung.

Abstract: Stress is the magnitude and direction of forces acting on a body, and strain is the magnitude and direction of deformations. Constitutive equations define the relationship between stress and strain for any material. If the material can be considered homogeneous, isotropic, and elastic--that is, if the mechanical properties are uniform and independent of direction and the deformations are reversible--the constitutive equations are greatly simplified and problems of physiological interest become more tractable. Material properties may be expressed as linear elastic constants or a strain energy function. Strain energy is most suitable for large-deformation nonlinear elasticity, but such analyses are extremely complex. Theoretically, linear elasticity is limited to very small deformations, but its applicability can be expanded by considering perturbations from an initial prestressed state, but using material properties that are functions of the initial conditions. Two independent elastic constants, the bulk modulus for volume change and the shear modulus for shape change, are required to define the material properties. For problems in which the geometry of the body and the applied forces are too complex to allow an analytic solution, the body may be broken up into many small, simple elements, and the resulting matrix of equations may be simultaneously solved by a computer. The disadvantage of this finite-element analysis, in addition to its inherent complexity, is that solutions are in terms of numbers rather than equations, and determining the effect of parameters requires that a number of sample problems be solved. Nevertheless, because of its immense power, this technique has an important place in lung mechanics.

Effect of State of Stress on Velocity of Low-Amplitude Compression Waves Propagating along Principal Stress Directions in Dry Sand.

Abstract: : Little research has been performed in which the effect of biaxial and triaxial states of stress on the propagation velocity of compression and shear waves has been investigated. Therefore, a triaxial testing device was constructed, and an initial test series was performed to determine the relationship between propagation velocities and state of stress in a dry sand. The testing device was constructed of reinforced steel and was designed to hold a cubic soil sample measuring 7 ft (2.1 m) on a side. Rubber membranes were placed between the soil and three mutually perpendicular walls of the cube, corresponding to the three principal planes. Stress and strain measuring devices were also placed in the soil. The effects on compression of the sample were determined. Structural anisotropy caused a variation between principal stress axes of about ten percent in velocity at a given pressure. Stress history resulted in no noticeable variation in P-wave velocity and, therefore, was neglected. Biaxial and triaxial loading results lead to the same conclusion, namely that the velocity of compression waves propagating along principal stress directions in dry sand as low-amplitude body waves depends only on the stress in the direction of wave propagation.

Prediction of the stress-strain curve of a short-fibre reinforced thermoplastic

Abstract: Analytical work has been performed to predict the stress—strain curve of a carbon fibre reinforced polyamide 66. A typical stress—strain curve of this composite consists of three stages. Beyond the first linear stage the change of slope of the curve is attributed to the initiation and extension of cracks at fibre ends. Several theoretical models have been developed to take into account the development of cracks at various loading levels. Fibre volume-fraction, aspect ratio and orientation as well as fibre and matrix elastic properties and interface energies are the major parameters considered. The theoretical predictions are in close agreement with the experimental data.

Goodness-of-Fit of the Ramberg-Osgood Analytic Stress-Strain Curve to Tensile Test Data

Abstract: One form of the Ramberg-Osgood analytic approximation of the stress-strain curve, which uses the 0.2% offset yield stress as one of the three parameters, has recently been approved for inclusion in Military Standardization Handbook-5. Using the root-mean-square error as a criterion, the fit of this formulation to data from 2357 tension tests of various materials was found to be excellent. In 90% of the tests, the root-mean-square error in stress was less than 1% of the yield stress and in half the tests the error was less than 0.4% of the yield stress.

Method analyzes analogue plots of paperboard stress-strain data*

Abstract: KEYWORDS One of the most important properties of paperboard is characterized by the Stress-strain properties analogue plot of stress vs. strain obtained from an edgewise compression Paperboards loading test. A method is given for determining the average stress-strain Compression tests curve for a group of curves by the use of representative models. An approximate method also allows data be read from a stress-strain curve so the analysis can be performed with a hand calculator.