Stress-strain Graph Research Articles

Fatigue Life Prediction of a Rocket Combustion Chamber

Cryogenic engines are commonly used in rockets for launching geosynchronous class satellites. The thrust chamber of cryogenic engines is generally of double walled construction. A high conductivity copper alloy is usually selected for the inner wall in regions of high heat flux and for other regions stainless steel is chosen. The failure of a thrust chamber is due to low cycle fatigue, creep of the inner wall, and thermal ratcheting. Present work deals with the study of different plasticity models for the cyclic stress analysis of a double walled cryogenic rocket engine thrust chamber. The work is done using ANSYS (Version 15) finite element code. Different plasticity models used for a simple cubic block showed that a combination of Chaboche's non linear kinematic hardening model in association with multilinear isotropic hardening and creep models is the best suited for cyclic stress analysis of the chamber. Cu-Cr-Zr-Ti alloy is investigated here as it is used in the inner wall of the thrust chamber. Material properties are taken from literature. A comparison of two dimensional (plane strain) and three dimensional cross section of thrust chamber is done. Cyclic life of the chamber is calculated from the cyclic stress-strain graph obtained from above analyses.

The Effect of Magnesium Addition on the Microstructure & Compressive Deformation Behavior of Al-Ca Alloy

The Al-Ca-Mg alloys containing varying amount of Mg are used to study the effect of Mg addition on their microstructure and deformation behavior at varying strain rate (0.01/s, 0.1/s, 1/s). The material is prepared using stir casting technique. The yield stress, flow stress and elastic limit are measured from the true stress-strain graph. The strain rate sensitivity and strain-hardening exponent were also determined for each material at different strain rates. The elastic limit decreases with increases in strain rate. The strain rate sensitivity m is found to be negative at a flow strain and invariant to the strain rate. Its microstructure reveals that the microstructural characteristics changes with Mg addition. The variation of microstructural features primarily leading to the variation of deformation behavior.

Winkler Springs (p-y curves) for pile design from stress-strain of soils: FE assessment of scaling coefficients using the Mobilized Strength Design concept

In practice, analysis of laterally loaded piles is carried out using beams on non-linear Winkler springs model (often known as p-y method) due to its simplicity, low computational cost and the ability to model layered soils. In this approach, soil-pile interaction along the depth is characterized by a set of discrete non-linear springs represented by p-y curves where p is the pressure on the soil that causes a relative deformation of y. p-y curves are usually constructed based on semi-empirical correlations. In order to construct API/DNV proposed p-y curve for clay, one needs two values from the monotonic stress-strain test results i.e., undrained strength (su) and the strain at 50% yield stress (e50). This approach may ignore various features for a particular soil which may lead to un-conservative or over-conservative design as not all the data points in the stress-strain relation are used. However, with the increasing ability to simulate soil-structure interaction problems using highly developed computers, the trend has shifted towards a more theoretically sound basis. In this paper, principles of Mobilized Strength Design (MSD) concept is used to construct a continuous p-y curves from experimentally obtained stress-strain relationship of the soil. In the method, the stress-strain graph is scaled by two coefficient NC(for stress) and MC(for strain) to obtain the p-y curves. MC and NC are derived based on Semi-Analytical Finite Element approach exploiting the axial symmetry where a pile is modelled as a series of embedded discs. An example is considered to show the application of the methodology.

Experimental Shear Stress Analysis of the Thin Walled Aluminum Hollow Shaft under Torsion

In this experimental study, maximum torsion shear stresses occurring on the hallow aluminum shaft under various small torsion loads were measured with strain gauge, data acquisition cards and computer. Special software was developed to measure maximum strain and stress on the thin aluminum hollow shaft. Stress values occurring on the aluminum hallow shaft under various small loads were measured with strain gauge and those strain values were transmitted to computer directly with data acquisition cards. Using the strain, the load and other constant values of the material (Torsion stress, outside and inside diameters of shaft, length of shaft, shear stress modulus, applied torque loads, twist angle of shaft etc) the stress values occurring on the hallow shaft are calculated by computer program and the stress-strain graph is drawn on the computer screen automatically [Refer to table1 Fig. 2,3,4 ,5 and . In this experimental study, the theoretical knowledge given in the books and experiment results obtained under laboratory conditions were compared with each other. The obtained results were almost same. Similar experimental application could be used for real applications in car industry and mobile machines [.

The Effects of Copper Addition on the compression behavior of Al-Ca Alloy

The Al-Ca-Cu alloys containing varying amount of Cu are used to study the effect of Cu addition on their deformation behavior at varying strain rate (0.001/s, 0.01/s, 0.1/s, 1/s).The material is prepared using stir casting technique The yield stress, flow stress and elastic limit are measured from the true stress-strain graph .The Strain Rate sensitivity and strain hardening exponent are also determined for each material at different strain rate. The Strain Rate Sensitivity of this alloy is very low. These values strongly demonstrate that compressive deformation of Al-Ca-Cu alloys almost independent to the strain rate at room temperature deformation.

A method for intermediate strain rate compression testing and study of compressive failure mechanism of Mg-Al-Zn alloy

Obtaining meaningful information from the test results is a challenge in the split-Hopkinson pressure bar (SHPB) test method if the specimen does not fail during the test. Although SHPB method is now widely used for high strain rate testing, this limitation has made it difficult to use it for characterization of materials in the intermediate strain rate range (typically 10−1000 s−1). In the present work, a method is developed to characterize materials in the intermediate strain rate range using SHPB setup. In this method, the specimen is repeatedly tested under compression at a given strain rate until failure is achieved. The stress–strain graphs obtained from each test cycle are used to plot the master stress–strain graph for that strain rate. This method is used to study the strain rate dependence of compressive response of a Mg-Al-Zn alloy in the intermediate strain rate range. A remarkable difference is observed in the failure mechanism of the alloy under quasi-static and intermediate strain rate compression. Matrix cracking is the main failure mechanism under quasi-static compression, whereas shattering of intermetallic precipitates, along with plastic deformation of the matrix, is discovered to become prominent as the strain rate is increased.

Effect of calcium addition on the microstructure and compressive deformation behaviour of 7178 aluminium alloy

Aluminium 7178 alloys containing 1% calcium are used to study the effect of calcium addition on their microstructure and compressive deformation behaviour. The compressive deformation behaviour of aluminium alloy containing 1% calcium is studied at varying strain rates (10 −2–10/s). The material is prepared using stir casting technique. The yield stress, flow stress and elastic limit are measured from the true stress–strain graph. The strain rate sensitivity and strain-hardening exponent was also determined for each material at different strain rates. Its microstructural characterization reveals that Ca particles act as grain refiners for primary base alloy and helps in improving the strength of the virgin alloy. An empirical relationship has been proposed to predict the flow curve of the alloys as a function of strain and strain rate.

Computer Simulation of Failure Process of a Fiber-reinforced Concrete Composite with Randomly Distributed Fiber Clusters

Fiber-reinforced concrete (FRC) composites to date are not fully researched with regard to the mechanical behavior of the random distribution of the fibers inside the matrix, which tend to bundle (fiber clusters). In this work we study the influence of the random distribution of fibers in the matrix by means of computer modeling applied to structural plane specimen subjected to tension loading. Increasing the tension load the failure will appear first in the weak concrete zones induced by the random distribution of inclusion elements. These failure elements are now modified as air elements, and the process goes on until collapse. As a result of this process the stress—strain plots of the sample until failure, and the stress—strain graph at the time of gradual application of the tension stress are found. We compare the obtained results with Kerner`s model. Computer modeling is achieved by the ANSYS program coupling a subroutine written in APDL language.

Tensile Strength and Ductility of Al-MT (MT = Fe, Ni) Intermetallic Alloys

In this work, FeAl and NiAl intermetallic alloys were produced by conventional casting using SiC crucibles. Li and Ni elements with 1, 3, and 5% were added to the AlFe intermetallic compound. In the case of NiAl intermetallic, the alloy' composition was based on (Ni55Fe5)Al with additions of 1, 3, and 5% of Li. After casting, the ingots were homogenized to minimize the thermal vacancy effects. For the AlFe ingots, the annealing treatments were carried out at 300°C during 170 hours. In the case of ALNi alloys, the annealing were performed at 400°C over 144 hours. Mechanical tests were carried out in both as cast and homogenized specimens. The experimental results are displayed as a stress-strain graph. The Li additions improve the percent of elongation and the ultimate tensile strength of the AlFe alloy. Additions of Ni improve the yield strength. In the AlNi intermetallic alloy, the best results were obtained with 5% Li additions. The tensile ductilities in intermetallic systems are improved when a heat treatment is used.

Randomness and slip avalanches in gradient plasticity

While localization of deformation at macroscopic scales has been documented and carefully characterized long ago, it is only recently that systematic experimental investigations have demonstrated that plastic flow of crystalline solids on mesoscopic scales proceeds in a strongly heterogenous and intermittent manner. In fact, deformation is characterized by intermittent bursts (‘slip avalanches’) the sizes of which obey power-law statistics. In the spatial domain, these avalanches produce characteristic deformation patterns in the form of slip lines and slip bands. Unlike to the case of macroscopic localization where gradient plasticity can capture the width and spacing of shear bands in the softening regime of the stress–strain graph, this type of mesoscopically jerky like localized plastic flow is observed in spite of a globally convex stress–strain relationship and may not be captured by standard deterministic continuum modelling. We thus propose a generalized constitutive model which includes both second-order strain gradients and randomness in the local stress–strain relationship. These features are related to the internal stresses which govern dislocation motion on microscopic scales. It is shown that the model can successfully describe experimental observations on slip avalanches as well as the associated surface morphology characteristics.

Numerical simulation of compaction bands in high-porosity sedimentary rock

Geologists have recently discerned naturally occurring discrete localized planar zones of deformation, associated with compaction of initially high-porosity rock. Such compaction bands may influence fluid transport, and stress/strain distribution in sedimentary formations. In order to gain insight into the formation mechanisms of compaction bands under a variety of boundary conditions, we developed a discrete model, in which the material is represented as a hexagonal lattice of springs that can transfer only normal forces (Central Force Spring model). The model easily allows for a discrete statistical distribution of material properties at a physically relevant scale. The occurrence of grain crushing and porosity reduction is represented by a change in the equilibrium length and elastic properties of each element that exceeds a certain stress threshold. Parametric analysis is conducted to explore and predict the conditions under which compaction bands form and develop. Our results also duplicate the different types of compaction propagation, observed in laboratory tri-axial compression experiments. The most important result of the simulations is the evaluation of the role of disorder. In our analysis, the differences in the patterns due to the extent of disorder in material's properties are systematically studied. Patterns resulting from different elastic mismatches at the boundaries are examined as well. Both of these parameters modulate the compaction nucleation sites. As a result, different patterns of compaction are generated in a competition between the elastic mismatch and the disorder. The case with no disorder allows compaction to be dominated by the large values of elastic mismatch and promotes a discrete mode of propagation starting from the specimen's boundaries. Larger values of disorder shift the nucleation sites into the interior of the specimen and promote the homogeneous front advance. Still larger disorder resulted in diffuse compaction inside the specimen. The origin of the distinct macroscopic differential stress vs. axial strain curves observed in laboratory experiments can be understood from our parametric analysis. If a material is sufficiently homogeneous, large stress drops, originating due to the elastic mismatch, will characterize its stress–strain graph. For a non-homogeneous material, the stress drops, originating mainly due to the large disorder, will be small and quite frequent. These important features have not yet been explained in the literature, although they were observed in the experiments.

Update on a class of gradient theories

This article, written in honor of Professor Nemat-Nasser, provides an update of the standard theories of dislocation dynamics, plasticity and elasticity properly modified to include scale effects through the introduction of higher order spatial gradients of constitutive variables in the governing equations of material description. Only a special class of gradient models, namely those developed by the author and his co-workers, are considered. After a brief review of the basic mathematical structure of the theory and certain gradient elasticity solutions for dislocation fields, the physical origin and form of the gradient terms (for all classes of elastic, plastic, and dislocation dynamics behavior), along with the nature of the associated phenomenological coefficients are discussed. Applications to the interpretation of deformation patterning and size effects are given. Two new features are noted: the role of wavelet analysis and stochasticity in interpreting deformation heterogeneity measurements and serrations of the stress–strain graph.

半導体レーザーによる血管と人工血管の吻合についての実験的検討

We experimentally evaluated diode laser welding between the vessel and artificial graft by tension/strain characteristics. We used extracted fresh porcine coronary artery strip, which the intima was removed intentionally, and collagen-coated knitted dacron. graft (Hemashield). An 830nm diode laser (power density, 57W/cm2) was employed to make welding with contact irradiation method, after topical application of indocyanine green dye (peak absorption, 805nm) and compression (3.5kg/cm2) of irradiation spot. The laser irradiation time was 30s in all. The specimens were strained axially until ultimate breakage occured in order to draw a stress-strain profile graph. We compared welded vessel-graft tissue group with welded vessel-vessel tissue group. Welded vessel-graft tissue (27.9±1.9g/mm2, n=10) withstood significantly higher stress(p<0.01) than welded vessel-vessel tissue (17.1±1.9g/mm2, n=10). No significant differences in strain limits of Hook's law, which was relative length until Hook's law could not be applied, were noted between welded vessel-graft tissue group and welded vessel-vessel tissue group. We obtained Young's modulus from a stress-strain profile graph. There was the significant difference in Young's modulus between the two groups (1.24±0.09×106dyn/cm2vs. 2.29±0.22×106dyn/cm2, n=10, p<0.05). And then, histrogical study of welded vessel-graft tissue showed that the vascular collagen fibers melted and invaded into fibers of the knitted dacron graft on the irradiation spot.

低強度半導体レーザーを用いた血管吻合についての基礎検討

We experimentally studied optimal conditions of diode laser vascular welding and characteristics of stress-strain profiles of welded vascular tissues. We used extracted fresh porcine coronary artery strip, which the intima was removed intentionally. An 830nm diode laser (power density, 57W/cm2) was employed to make vascular welding with contact irradiation method, after topical application of indocyanine green dye (peak absorption, 805nm) and compression (3.5kg/cm2) of irradiation spot.The specimens were strained axially until ultimate breakage occurred in order to described a stress-strain profile graph. The optimal irradiation time was 30s on our conditions. we obtained Young's modulus from a stress-strain profile graph. Young's modulus was 4.3×106 dyn/cm2 in vascular tissue, and 1.6×106 dyn/cm2 in welded vascular tissues. We calculated Young's modulus of welded part. It was 2.5×106 dyn/cm2 in welded part.

Biomechanical properties of normal tendons, normal palmar aponeuroses, and tissues from patients with Dupuytren's disease subjected to elastase and chondroitinase treatment

Normal tendons, normal palmar aponeuroses and palmar aponeuroses from patients with Dupuytren's disease were subjected to elastase or chondroitinase treatment. Young's modulus was derived from the linear portion of stress-strain graph. It showed the lowest value for the apparently normal palmar aponeuroses and the highest value for tendon samples. Elastase treatment caused an increase of extensibility and a reduction of Young's modulus of normal palmar aponeuroses and tendons, but not of contracture bands. In normal tendons, normal palmar aponeuroses and apparently normal palmar aponeuroses residual strain and hysteresis loop increased significantly as a linear function of the amount of digested elastin. In contrast these biomechanical parameters were not affected significantly in contracture bands. In normal and apparently normal areas incubation with chondroitinase ABC resulted in a significant increase of residual strain and, as opposed to elastase, a decrease of normalized hysteresis loop. In contracture bands, however, these biomechanical parameters remained unchanged.

Laser-assisted fibrinogen bonding of vascular tissue

Characterization of the stress-strain profiles of welded tissue would provide an additional means of analyzing this new technology and comparing it with alternative anastomosing techniques. Rabbit longitudinal aortotomies were repaired with either 7-O polypropylene sutures or an 808-nm diode laser (power density, 4.8 watts/cm 2) after topical application of fibrinogen mixed with indocyanine green dye (peak absorption, 805 nm). The rabbits were sacrificed between 0 and 28 days, and the fresh aortic specimens were strained axially in diluted plasma solution until ultimate breakage occurred in order to produce a stress-strain profile graph. No significant differences were noted between sutured and bonded aorta at any time interval. Nonincised aortic tissue (378 lb/in 2) withstood significantly higher stress ( P < 0.05) than both sutured (257 lb/in 2) and bonded (210 lb/in 2) groups at the time of creation. By 7 days after operation, however, no significant differences were noted among any of the three groups. At 28 days after operation, the laser-bonded aorta was significantly stronger than the control aorta ( P < 0.05). The only significant difference in modulus (stretchability) identified the sutured aorta (373 lb/in 2) to be more rigid than the control aorta (231 lb/in 2) ( P < 0.05). Both sutured and laser-bonded anastomoses are weaker than control aorta initially; however, after an early critical period, both treatments achieve the strength of control aorta. By 1 month postoperatively, sutured anastomoses have the disadvantage of being less distensible.

かまぼこにおけるデンプンの効果

Starch is widely used to make Kamaboko. In this paper, we describe an experimental study of the effect of starch on the physical properties of Kamaboko: The breaking stress and breaking strain are measured with OKADA's gelometer on specimens containing various amounts of starch and water, and the score of texture are decided by the sensory test. Results obtained are as follows. 1) A similar score of synthetic evaluation seems to describe a similar half-ellipse on the stress-strain graph. The half-ellipse having a high score is located at the centric position with a high strain value. 2) At higher concentrations of starch, the value of stress increases and that of strain decreases gradually after the initial increase. 3) At higher amounts of moisture, the value of stress decreases rapidly and that of strain decreases gradually.

Rubber in Compression

Abstract The effects of shape and surface conditions of rubber used in compression have remained somewhat of a mystery because of the apparently conflicting results often obtained. It is to be hoped that the work herein described will: (1) explain some of the difficulties encountered; (2) establish a simple and reasonably accurate procedure for predetermining the compression stress-strain performance of many of the commonly used shapes, and (3) encourage an extension of this work to include more complicated shapes, and to provide further refinement of the results. Compression uses of rubber doubtless far exceed in number the shear and tension uses for industrial applications, and warrant much work in determining the relationships involved, at least to the extent of establishing empirical rules of sufficient scope and accuracy for practical use. The erratic nature of compression-test results has made it difficult to correlate data reported in the technical articles on this subject. It is herein indicated that much of this difficulty may be explained by the condition of the surfaces, the manner of applying the load, discrepancies in hardness measurements, variations in the actual stiffness of the rubber used, and the fact that the stress-strain graph is not a straight line.