Levels Of Tensile Strain Research Articles

Effect of Fatigue Step Loading Sequence on Residual Strength

Abstract Miner's rule is often assumed to hold in accelerated fatigue tests. This rule implies that the order in which loads are applied is not significant. Whether particular loads are applied early in the test or later is unimportant; they are expected to cause the same amount of damage if they are imposed for the same number of cycles. In order to test this hypothesis, we have investigated the effect of loading sequence on residual strength using two levels of tensile strain and several representative rubber compounds. In all cases, a series of increasing strains was found to reduce the strength to a greater degree than the same strains applied in decreasing order. Thus, Miner's rule does not hold for the fatigue failure of these compounds. However, the relative rankings of the compounds remained the same in both step-up and step-down strain sequences.

Development of a Method for Measuring Residual Strain Based on Small Deformation Characteristics of Graphite Materials.

Development of a method for measuring the residual strain in graphite components in the gas-cooled nuclear reactors which is nondestructive is a major research aim. In order to measure the residual strain in graphite components, the applicability of a micro indentation method was investigated using a micro hardness testing machine. In the test indentation load to depth characteristics and micro hardness were determined at several levels of tensile residual strain in the graphite material. We describe the experimental results and discusses the applicability of the micro indentation method to residual strain measurement for graphite components.

Compressive Strength Of Reinforced Masonry under Lateral Tension

Shear walls are subjected to biaxial in-plane stresses when resisting seismic or wind loadings. Vertical tensile cracking reduces the compressive strength of walls in a direction normal to the tensile strain. This has been widely studied and accepted for reinforced concrete. However, for reinforced masonry there are no data available to predict the reduced compressive strength and behavior for walls with lateral tensile strains. To provide data for masonry, a biaxial test frame was constructed capable of loading masonry panels 80 cm (32 in.) high by 120 cm (48 in.) wide in combined compression and tension. Reinforced masonry panels subjected to various levels of lateral tensile strain were loaded to vertical compressive failure. Results from a test series of wall panels tested under various levels of lateral tension and vertical compression were used to establish a model to predict the reduction in compressive strength due to the lateral strain field.

Fracture Process Control For A Peel-Apart Imaging Film

AbstractPeeling delamination and image-layer fracture of a multilayer imaging film is analyzed by a simple beam approximation. Criteria for propagation of the delamination cracks and tensile failure of the imaging layer are established. The critical role of substrate strain in controlling tensile strain in the imaging layer is explored. For the case of a thin imaging layer with a fracture strain below a critical level, image layer fracture occurs while the leading-edge delaminations length is comparable to the layer thickness. Experimental Helios film image quality is optimized at a small level of substrate tensile strain where delamination length at leading and trailing edges of small holes is balanced and small and where hole size is minimized.

In vitro strain measurements in the condylar process of the human mandible

Although there have been a number of experimental studies of temporomandibular joint loading, the precise relation between condylar load and condylar strain is incompletely understood. This in vitro study determined the magnitudes and directions of the principal components of strain on the four surfaces of the condylar process of human cadaver mandibles during loading with selected simulated muscle forces, with simultaneous measurement of occlusal and joint forces. Rosette strain gauges were placed on each of the four surfaces and the mandibles were loaded by a load cell to simulate the action of the masseter and medial pterygoid muscles. Force and strain values were measured at five different bite positions and nine different positions of the resultant muscle force. Forces and strain values were highest when the resultant muscle force was closest to the joint and the bite position was furthest from the joint. The ratios of bite force to joint force and the ratios of forces between the two joints conformed to theoretical predictions of many previous models, with the balancing-side joint being loaded more heavily than the working-side joint. At all gauge positions the maximum principal strain was tensile, the minimum principal strain was compressive, and the absolute strain values were correlated with the magnitude of the force on the condyle. However, under the chosen loading regimen, the ratio of compressive to tensile strain differed among the four surfaces. The highest levels of tensile strain occurred on the anterior and lateral surfaces and the highest compressive strain occurred on the posterior surface. It was not possible to detect significant changes in strain patterns due to bite position or muscle force position, that were independent of the force magnitudes.

Tensile Stress-Strain Characteristics of Lightly Cemented Sand

Abstract Laboratory tensile and unconfined compression test results on lightly cemented sand specimens are reported. Type I portland cement was mixed with sand in proportions of 4, 6, and 8% by weight to prepare the specimens. Tensile strength was determined by indirect tensile strength testing and direct tension testing. The variation of tensile strain with stress in indirect tensile strength tests was measured by a computer-aided image analysis method. Based on the test results, tensile and compressive strengths and strain levels at failure have been determined and compared. Nondimensional tensile stress-strain relationships in the form of a rectangular hyperbola as obtained from the indirect tensile strength tests and direct tension tests have been developed.

Role of Ag additions in the microstructural development, strain tolerance, and critical current density of Ag-sheathed BSCCO superconducting tapes

Ag-sheathed tapes of Bi–Sr–Ca–Cu–O (BSCCO) and BSCCO–Ag superconducting cores were made by a powder-in-tube technique and subjected to repeated cycles of pressing and heat treatments. These thermomechanical treatments resulted in enhanced texturing and grain growth that improved the critical current density (Jc). Additions of Ag to the BSCCO core further increased texturing and brought an additional improvement in Jc. Strain tolerance of the tapes was evaluated by measuring Jc before and after application of a predetermined level of tensile strain in a uniaxial mode. The fraction of Jc retained after the strain application was higher in the BSCCO–Ag composite tapes than in the monolithic BSCCO. For a 1.2% applied strain, 90% of the initial Jc was retained in the BSCCO–Ag composite tape, compared to only 40% in the monolithic BSCCO tapes. The higher strain tolerance of the BSCCO–Ag tapes may be related to improved mechanical properties (strength, flexibility, and fracture toughness) and grain connectivity due to Ag addition.

Evaluation of stresses in the edge effect zone in tension of composite laminates

i. A specific feature in the loading of rectangular specimens made of laminate materials is the occurrence of high stress peaks along the line of intersection of the lateral side with the interlaminar plane. It is accepted practice in the mechanics of composite laminates to call edge effects the effects connected with large stress gradients localized near . this line [i]. Among the edge effects are premature delamination of material before the load bearing capacity of the specimen is exhausted [i] and the characteristic broadening of the lateral side (swelling) under tensile loading [2]. The onset of delamination was noted at certain levels of tensile strain [3, 4] depending on the nature of the stacking. A change of tensile strength in dependence on the stacking sequence was noted in [i, 5].

Low cycle fatigue behaviour of a 1Cr-Mo-V steel with bainite and ferrite microstructure

A 1Cr-Mo-V turbine rotor steel forging, heat treated to obtain a bainite-20% ferrite microstructure, has been investigated for low cycle fatigue behaviour at room temperature and 535°C. In addition to establishing life expectancy curves, cyclic stress response and cyclic stress/strain curves were derived and the influence of time-dependent effects on high temperature low cycle fatigue life was also determined by introducing varying hold times at the peak tensile strain level of the fatigue cycle. The life expectancy curve obtained is comparable to that reported for the bainitic structure in this steel. Introduction of a dwell period of 5 min is found to reduce the low cycle fatigue life by a factor of 1.6.

Strain gauge measurement of mesokinetic movement in the lizard Varanus exanthematicus.

Single-element strain gauges were placed across the mesokinetic joint of the skull of the savanna monitor lizard, Varanus exanthematicus Bosc, in order to document the extent and timing of mesokinetic movement. In addition, rosette strain gauges were placed on various points of the palato-maxillary segment. Strain recordings and simultaneous cineradiographic films or videotapes were taken during normal feeding activities, including the strike, prey manipulation, ingestion and pharyngeal compression. Tensile strain, indicating lowering (retraction) of the palato-maxillary segment, was observed during all stages of feeding. Compressive strain, indicating lifting (protraction) of the palato-maxillary segment, generally appeared briefly in the strike and during pharyngeal compression. Maximum tensile strains were always larger than maximum compressive strains within each sequence. The highest levels of tensile strain occurred during prey manipulation periods, which were characterized by isometric biting. Strain on the palato-maxillary segment revealed a pattern of timing similar to the one at the mesokinetic joint, although strain levels were at least an order of magnitude lower. These data directly contradict conventional models of the function of the kinetic skull in lizards. We conclude that the kinetic apparatus in lizards is not a mechanism for actively moving the palato-maxillary unit and is therefore not a mechanism for increasing gape or actively controlling upper jaw movements.

Utility of the Green-Rivlin Theory in Polymer Mechanics

For the case of stress relaxation at constant strain, the Green-Rivlin theory for nonlinear materials with memory predicts that the stress is a power series in the strain where the coefficients, called kernels, characterize the material. This prediction of the theory has been tested using data obtained on the polycarbonate of bisphenol A in the timescale range 10–1000 sec and temperature range 23°–130°C. At each temperature level of this study, the two leading terms of the power series account for actual behavior within the standard deviation of the experimental data (3%) up to the level of tensile strain where instability (cold-drawing) occurs. The first (``linear'') kernel decreases monotonously with temperature as Tg is approached, but the second and higher kernels each vary with temperature in a complex manner. The utility of summarizing the nonlinear behavior of polymers by kernel functions is appraised and discussed in the light of recent findings on the range of validity of linear viscoelasticity theory. It is concluded that the second and higher kernels of the theory do not have any obvious physical significance. It is also suggested that the first and the second kernels might represent adequately by themselves the nonlinear viscoelastic behavior of glassy, amorphous polymers up to about 5% strain, whereas the third and higher kernels appear in addition to be necessary for semicrystalline polymers.