Showing papers on "Stress–strain curve published in 1991"

Compressive behaviour of concrete at high strain rates

Abstract: Experimental techniques commonly used for high strain-rate testing of concrete in compression, together with the methods used for measurement and recording of stress and strain, are critically assessed in the first part of this paper. The physical capability of each loading method is discussed and some consideration is given to the definitions used for specifying the loading rate. The second part reviews the dynamic compressive strength (mostly uniaxial rather than bi- or triaxial) of plain concrete, while in the third part a review on deformation behaviour indicates that uncertainty and disagreement exist concerning changes in axial strain at high strain rates.

Mean stress effects on low cycle fatigue for a high strength steel

Abstract: — ASTM A723 Q & T steel with a yield strength and ultimate strength of 1170 and 1262 MPa respectively was evaluated for mean stress-strain effects under smooth specimen axial strain controlled low cycle fatigue conditions with strain ratios R of −2, −1, 0, 0.5 and 0.75. Cycles to failure ranged from 15 to 105. Cyclic stress-strain response based upon half-life hysteresis loop peaks were similar for all R ratios. Mean stress relaxation occurred for R≠−1 only when plastic strain amplitudes were present and this occurred above total strain amplitudes of 0.005. Thus, mean stress relaxation was completely dependent upon cyclic plasticity. Mean strains did not affect low cycle fatigue life unless accompanied by half-life mean stress. Tensile mean stress was detrimental and compressive mean stress was beneficial and these effects only occurred at strain ampltidues below 0.005. Three different mean stress models were used to evaluate the low cycle fatigue data and the SWT log-log linear model best represented the data. These results can be used with the local notch strain fatigue life prediction methodology.

Micromechanical modeling of fiber/matrix interface effects in transversely loaded SiC/Ti-6-4 metal matrix composites

Abstract: The transverse tensile behavior of a composite composed of unidirectional silicon-carbide fiber (Textron SCS-6) in a Ti-6AL-4V matrix is examined with emphasis on the effects of fiber-matrix interface strength. The residual stresses as a result of a mismatch in the coefficients of thermal expansion of silicon carbide and titanium are estimated analytically and compared with measurements made using X-ray diffraction techniques. Idealizing the composite as a regular rectangular array of fibers in an elasto-plastic matrix, the transverse tensile stress-strain behavior is predicted under the assumptions of an infinitely strong interface as well as an interface without tensile strength. These results are compared with experiments conducted at three different temperatures. The agreement between experiment and predictions based on an interface without tensile strength is extremely close. The modeled stress-strain curves predict a well-defined knee in the transverse tensile stress-strain curve associated with the separation of fiber and matrix at their interface. The same stress-strain behavior is observed experimentally. Results of edge replica experiments and mechanical unloading from stress levels above the knee are also presented as additional evidence of the association of fiber-matrix separation with the knee in the transverse tensile stress-strain curve.

Do fibers increase the tensile strength of cement-based matrixes

Abstract: Many of the current applications of fiber reinforced concrete involve the use of fibers ranging around 1 % by volume of concrete It is usually assumed that fibers do not influence the tensile strength of the matrix, and that only after the matrix has cracked do the fibers contribute by bridging the cracks Recently, it has been possible to incorporate relatively large volumes (ranging up to 15%) of steel, glass, and synthetic fibers in concrete With such a large volume of fibers in concrete, some evidence presented in this paper indicates that the fibers may substantially increase the tensile strength of matrixes If this is true, then it is important to define conditions under which such beneficial interactions can occur

The Generalized Local Stress Strain (GLOSS) Analysis—Theory and Applications

Abstract: The underlying theory relates redistribution of inelastic stresses at a given location under consideration to the uniaxial stress relaxation process. GLOSS analysis is emerging as a useful technique for determining multiaxial stress relaxation, follow-up, creep damage, inelastic strain concentrations and low-cycle fatigue estimates, limit analysis and issues pertaining to stress-classification

Tensile and Fatigue Behavior of Silicon Carbide Fiber‐Reinforced Aluminosilicate Glass

Abstract: The onset of damage accumulation in ceramic-matrix composites occurs as matrix microcracking and fiber/matrix debonding. Tension tests were used to determine the stress and strain levels to first initiate microcracking in both unidirectional and cross-ply laminates of silicon carbide fiber-reinforced aluminosilicate glass. Tension–tension fatigue tests were then conducted at stress levels below and above the matrix cracking stress level. At stress levels below matrix microcracking, no loss in stiffness occurred. At stresses above matrix cracking, the elastic modulus of the unidirectional specimens exhibited a gradual decrease during the first 10 000 cycles, and then stabilized. However, the cross-ply material sustained most of the damage on the first loading cycle. It is shown that fatigue life can be related to nonlinear stress–strain behavior of the 0° plies, and that the cyclic strain limit was approximately 0.3%.

Biaxial Testing of Membrane Biomaterials: Testing Equipment and Procedures

Abstract: A testing facility for measuring the biaxial mechanical properties of highly deformable membranes is described. Forces are applied, via strain-gauge force transducers, to four points on each side of an initially square 12 to 25 mm membrane sample to produce biaxial extensions of up to 80 percent of undeformed length. Strain is estimated from the displacement of markers bounding a 1 to 2 mm central square. The accuracy of stress and strain field measurements has been assessed by finite element analysis of a biaxially-loaded isotropic elastic membrane. Major advantages of the present system over those previously described in the literature are that 1) sample mounting procedures are simplified, 2) there is provision for independent adjustment of stress field uniformity and measurement of the applied point forces and 3) faster strain rates can be imposed on the relatively small samples tested.

Fiber-Optic Sensors for Concrete Strain-Stress Measurement

Abstract: The paper presents a nondestructive testing method based on fiber optics for measuring strain and stress in concrete structures in situ. When an optical fiber is embedded in concrete, and its refractive index, dimension, and/or shape are changed as a result of the surrounding matrix deformation, the characteristics of the light signal transmitted along the fiber are modified. Optical techniques capable of determining the changes in light characteristics are described. The two most promising techniques for concrete-structures diagnostics are demonstrated in the laboratory using concrete cylinders subjected to unconfined uniaxial compression with optical fibers embedded in a direction parallel and perpendicular to the aplied strain (load). Encouraging experimental results indicate that fiber-optic sensors can be a feasible tool to determine strain/stress distribution in buildings and infrastructures.

Thermal Cycling Induced Plastic Deformation in Solder Joints—Part I: Accumulated Deformation in Surface Mount Joints

Abstract: When an electronic package is subjected to thermal cycling, the solder joint interconnects are subjected to a complex stress system. If the stress is sufficiently large, the solder joint will show evidence of plastic flow along with microstructure coarsening and possible fatigue crack initiation and propagation. Plastic flow has not been studied as thoroughly as the later two phenomena although it is often observed at surface mount or through-hole solder joints. The thermal expansion mismatch between different materials in the package is responsible for the plastic deformation which accumulates with thermal cycling. In this study, the accumulated plastic deformation process is modelled with finite element (FE) methods and compared with experimental results. Lead-frame solder joints have been analyzed with a nonlinear FE program using temperature and time-dependent properties. Steady-state creep is considered using data for eutectic lead/tin solder which is described by a hyperbolic sine creep law: e = A(sinh Bσ)n dm exp(−Q/RT) . The analysis correctly simulates the large plastic flow found experimentally in a lead-frame solder joint. The resulting stress and strain distributions indicate possible failure modes which are not anticipated on the basis of uniform shear assumptions or predictable from an FE analysis of the initial geometry.

Behaviour of concrete spirally confined by fibreglass filaments

Abstract: Results are presented on the strength and deformation capacity of concrete transversely reinforced with fibreglass filaments (wires). A total of 33 cylinders confined with fibreglass wires were tested to obtain complete stress–strain curves in compression. The wires were 80% glass and 20% polyester resin matrix, and had a tensile strength of 300 ksi (2070 MPa). Based on the experimental data, an analytical equation was developed to predict the stress–strain curves of plain and fibreglass wire–confined concrete. The two constants in the equation were calibrated from the observed test results, so that only the strength of concrete was required to generate the stress–strain response of plain concrete, and the strength of plain concrete and the spacing of the fibreglass wires were required to generate the complete stress–strain response of fibreglass–confined concrete. Results of this study are compared with those reported for concrete confined transversely by steel reinforcement.

Structural plasticity: Theory, problems, and CAE software

Abstract: One dimensional stress-strain analysis one-dimensional stress-strain analysis software elastic stress and strain analysis yield criteria perfectly plastic stress analysis hardening plastic stress analysis.

The stress/strain behavior of aluminum matrix composites with discontinuous reinforcements

Abstract: The flow properties of a ductile Al alloy reinforced with SiC particulates and randomly oriented platelets have been investigated to establish trends with such variables as reinforcement volume fraction, size and aspect ratio. The experimental results are compared with the trends predicted by recent continuum calculations. The general agreement found between experiments and the calculations has established the following characteristic features of the flow strength. This strength is strongly influenced by reinforcement volume fraction ƒ, especially when ƒ is large ( ƒ > 0.3 ). Particulates and non-aligned platelets having aspect ratio 10:1 exhibit about the same strengthening.

Modelling the transient flow behaviour of dynamic strain ageing materials

Abstract: Stress and strain rate transients which accompany small perturbations from steady state deformation in the regime of dynamic strain ageing are modelled. The constitutive relation employed includes the local solute concentration at arrested mobile dislocations as a time dependent state variable. Using linear perturbation theory it is shown that four types of transient behaviour are possible: monotonic decay, oscillatory decay, oscillatory growth and monotonic growth of the perturbation. A transient behaviour map is developed which shows the transient behaviour as a function of the strain rate sensitivity of flow stress and the machine stiffness. The results of the analysis are compared with recent experimental measurements of transient yield behaviour associated with dynamic strain ageing.

Deformation and fracture of cork in tension

Abstract: Various properties related to the deformation and fracture of cork in tension were experimentally determined, including the Young's modulus, the stress and strain at fracture and the fracture toughnessKIc. The transverse isotropy of cork implies that there are three independent systems of mode I crack propagation andKIc was measured for each. The mechanisms of deformation and fracture were identified by SEM microscope observation ofin situ deformation and of the fracture surfaces and crack paths. Two fundamental mechanisms of fracture occur: crack propagation along the lateral cell walls in non-radial tension, withKIc = 94±16 kPam1/2 and crack propagation by breaking the cell walls in radial tension withKIc=125±14 kPam1/2. In radial tension, local fractures that do not propagate due to crack stopping were observed which lead to serrations in the tensile curves for that direction. The strain to fracture in this direction is considerably larger than in the perpendicular (non-radial) directions.

Failure by ductile cavity growth at a metal-ceramic interface

Abstract: The development of stress and strain fields in a metal bond layer between two ceramics is determined numerically for tensile loading normal to the layer. Apart from small regions near free edges of the specimen it is found that the elastic-plastic deformations in the metal layer follow closely a state of uniaxial straining, with the associated development of a high level of triaxial tension. This uniaxial strain state is used in a cell model analysis to study ductile failure in the metal layer by the growth of cavities at initially unbonded spots on the interface. For small isolated interface cavities the results are related to recent studies of cavitation instabilities in elastic-plastic solids subject to highly triaxial stress states. The predictions of the analyses are also discussed in relation to recent experimental results for metal bond layers between ceramics.

Elastic modulus of sifcon in tension and compression

Abstract: A graphical evaluation of various analytical models predicting the modulus of elasticity of fiber reinforced composites is first presented. Upper and lower bound solutions and their applicability to fiber reinforced concrete and slurry-infiltrated fiber concrete (SIFCON) are discussed. An experimental investigation of the elastic modulus of SIFCON in tension and compression is then described. Two different types of fibers, two different aspect ratios, seven different levels of volume fractions, and 4 different matirix compositions were used. The value of the modulus of elasticity is found to be dependent upon not only the peak compressive strength, but also factors such as fiber volume fraction, fiber aspect ratio, fiber orientation and alignment, and testing procedure. Experimental data are analyzed and conclusions are drawn.

Thermal cycling induced plastic deformation in solder joints. II. Accumulated deformation in through hole joints

Abstract: A thermal-cycled through-hole solder joint is studied. Nonlinear elastic/plastic solder properties at different temperatures and a steady-state creep law are used to characterize the deformation of the eutectic Pb-Sn solder. Large geometry changes in the solder and pin structure are observed experimentally. The deformation observed is much larger than expected from a simple thermal expansion mismatch calculation. This phenomenon is explained as a combination of plastic and creep deformations which accumulate during the thermal cycling. Because of the complexity of multiaxial stresses in the joint due to thermal expansion mismatch, finite-element analysis is required to characterize stress and strain in the solder joint. The large plastic deformation observed in the solder fillet is quantitatively simulated by the analysis. The majority of the deformation is a result of the time-dependent creep, while deformation occurring during the time-independent temperature change is minor. The displacement of the IC pins is recorded after each cycle and approaches the value observed in an actual joint after 1000 cycles. Thermal cycling fatigue life prediction based on uniform shear and the Coffin-Manson equation is found to be insufficient in dealing with the complex deformation mechanism of solder. >

Behavior of Concrete Under Triaxial Compressive-Compressive-Tensile Stresses

Abstract: Seventy-nine 10 x 10 x 55-cm prisms for triaxial compression-compression-tension specimens were tested. The tests were taken in a special device containing 2 compression testing apparatus to exert lateral compressive loadings and an ordinary universal material-testing machine to exert longitudinal tensile loading. One 3 mm fluorine-based resin sheet (Teflon) was used as a friction-reducing pad. Test results of strength and stress-strain relationships are analyzed, and formulas of concrete strength are suggested. Failure modes of specimens are also described.

Constitutive modeling of the effects of oxygen on the deformation behavior of silicon

Abstract: A systematic theory is presented that models the effects of interstitial oxygen on the deformation behavior of silicon. The theory is based on calculation of the dependence of the dislocation velocity on the applied stress in the crystal and determination of the locking and unlocking stresses for dislocation motion. Internal stresses in the oxygen-hardened crystals are modeled by the superposition of the unlocking stress, a back stress due to the interaction between mobile dislocations, and an internal stress that arises from the interaction between a dislocation and the oxygen cloud around other dislocations. The initiation of dislocation multiplication is modeled as a two-step thermally activated process; the first step is the unlocking of the dislocation and the second step is the formation of jogs along the dislocation line. The coupled model for oxygen transport and dislocation motion is used to simulate crystal deformation in dynamic experiments and to reproduce stress-strain curves. The predictions of the initial stage of deformation are in good agreement with the experimental data of Yonenaga et al. [J. Applied Phys. 56, 2346 (1984)].

Strain-rate sensitivity of mild steel grade St52-3N

Abstract: A study is made of the effect of strain rate on the strength of St 52‐3N mild steel, commonly used as deck plating in offshore structures. Stress‐strain curves are obtained in both tension and torsional shear at room temperature at strain rates from 10-4s-1 to 103s-1 and compared with previous work on mild steel. The tensile data show that the lower yield stress is approximately twice as strain rate sensitive as stresses in the hardening region and that the ultimate tensile strain is approximately unaffected by strain rate effects up to a strain rate of 20s-1. The torsion data extends to large strains (300%) and shows adiabatic thermal softening at the higher strain rates. The tension and torsion data show that the von Mises yield criterion overestimates the flow stress in pure shear. The material data have been used in determining the penetration resistance of deck structure to dropped objects such as drill collars and it has been found that strain rate effects are of minor importance for the structural ...

Low cycle fatigue life predictions for hollow tubes with axially loaded axisymmetric internal projections

Abstract: The finite element method has been used to study the monotonic and cyclic elastic–plastic stress and strain characteristics of hollow tubes with axisymmetric internal projections subjected to monotonic and repeated axial loading This paper compares finite element strain predictions with values estimated using simple notch stress–strain conversion equations for two geometries and a range of nominal stresses From this study, an intermediate equation (m = 05) is suggested for low cycle fatigue life predictions The results have been normalized with respect to material properties so that they can be applied to geometrically similar components made from other materials which can be represented by the same material models

Finite element method modeling of deformation behavior of two-phase materials part I: stress-strain relations

Abstract: A systematic study was undertaken to determine the effect of the strength ratio on the stress-strain behavior of various two-phase materials by the finite element method where the volume per cent of the second phase was varied from 20 to 80 vol.%. The strength ratio of the harder β phase to the softer α phase was varied from approximately 2 to 5 where the α phase strength (0.2% YS) was kept constant at 368 MPa. It was found that the flow stress of any given two-phase material did not vary linearly with the strength ratio. In addition, for a given strength ratio, the flow stress of the two-phase material did not vary linearly with volume per cent. For materials with less than 40 vol.% β phase, the increase in the strength of the two-phase materials with either volume per cent of β or strength ratio was very small. This was attributed to the fact that the softer α phase, being the matrix, could deform relatively freely without the phase β undergoing plastic deformation up to a plastic strain of 0.5%. When the volume per cent of β was much greater than 50 vol.%, the softer α phase could not deform freely without the harder β phase undergoing plastic deformation, resulting in increased flow stresses with increased strength ratios. Plateaux were observed in the plots of 0.2% and 0.5% off-set flow stresses as a function of the strength ratios. The strength ratio for which the plateau was observed was different for different α-β materials and was dependent on the volume per cent of the β phase and also on the plastic strain.