Uniaxial Tension Conditions Research Articles

Experimental Study of the High Temperature Mechanical Behaviors of TLP Bonding of Two Ni-Base Single Crystals

In this paper, the mechanical behavior of Ni-base single crystals joint created by TLP bonding is presented. Experimental study has been performed on the TLP single crystal under loading conditions of static uniaxial tension, creep and Three-points-bending (T-P-B) at temperature of 850 °C. Specimens made of the base material, Ni-base single crystal specimens without bonding, were also tested under the same loading conditions. The mechanical behaviors of TLP single crystal is compared to the behaviors of base material. It was found that the static strength of the TLP specimens with the boundary normal to the tensile direction was 63% of the strength of the base material. The creep strength and the fracture ductile strength was more than 57% and 55% of that of the single crystal base material, respectively. The macro and micro graphs of fracture surfaces of specimens indicated that the fracture modes of the samples were brittle fracture.

Lattice orientation effects on void growth and coalescence in fcc single crystals

Void growth and coalescence in fcc single crystals were studied using crystal plasticity under uniaxial and biaxial loading conditions and various orientations of the crystalline lattice. A 2D plane strain unit cell with one and two cylindrical voids was employed using three-dimensional 12 potentially active slip systems. The results were compared to five representative orientations of the tensile axis on the stereographic triangle. For uniaxial tension conditions, the void volume fraction increase under the applied load is strongly dependent on the crystallographic orientation with respect to the tensile axis. For some orientations of the tensile axis, such as [1 0 0] or [1 1 0], the voids exhibited a growth rate twice as fast compared with other orientations ([1 0 0], [2 1 1]). Void growth and coalescence simulations under uniaxial loading indicated that during deformation along some orientations with asymmetry of the slip systems, the voids experienced rotation and shape distortion, due mainly to lattice reorientation. Coalescence effects are shown to diminish the influence of lattice orientation on the void volume fraction increase, but noteworthy differences are still present. Under biaxial loading conditions, practically all differences in the void volume fraction for different orientations of the tensile axes during void growth vanish. These results lead to the conclusion that at microstructural length scales in regions under intense biaxiality/triaxiality conditions, such as crack tip or notched regions, the plastic anisotropy due to the initial lattice orientation has only a minor role in influencing the void growth rate. In such situations, void growth and coalescence are mainly determined by the stress triaxiality, the magnitude of accumulated strain, and the spatial localization of such plastic strains.

Local and Global Damages of Quasi-Brittle Material in Uniaxial Compression Based on Gradient-Dependent Plasticity

Theoretical relations among local and nonlocal damage variables in localized band as well as global damage variable according to the measured stress-strain curve of quasi-brittle material subjected to shear and tensile failures in uniaxial compression and in three-point bending were presented. The nolocal damage variable depends on the local counterpart and its second spatial gradient based on nonlocal theory. Analytical solution for the local damage variable was derived by substitution of the nonlocal damage variable for averaged damage variable in shear band and by using boundary condition as well as by resorting to the assumption that the actual thickness of shear band corresponds to the maximum local damage variable. It is found that local damage variable depends on the internal length parameter, coordinate, flow shear stress, shear strength, shear elastic and softening moduli. Assuming that the shear localization is initiated just at the peak strength, and that afterwards the strain-softening behavior of specimen occurs. The relation among shear strength, uniaxial compressive strength, flow shear and compressive stresses was established. The global damage variable was defined according to the measured stress-strain curve whether the post-peak response is snap-back or snap-through, which depends on the uniaxial compressive strength and flow compressive stress. A relation among local, nonlocal, and global damage variables in uniaxial compression was proposed analytically, and then a relation applicable to three-point bending was directly presented. The latter relation can be simplified for uniaxial tension condition if tensile stress is assumed to be uniform. Two examples were presented to investigate the two- and three-dimensional distributions of local damage variable in shear and tensile localized bands. The present analytical solutions for the distributed damage in shear and tensile localized bands qualitatively agree with the previous numerical predictions.

Quantifying the Confidence Levels of Deformation Measurements in Asphalt Concrete

Abstract An experimental approach for measuring surface strains in asphalt concrete (AC) samples is presented in this paper. It is equivalent to the local attachment of a large number of linear variable displacement transducers (LVDTs) with gage lengths ranging from 5 to 80 mm. The strain distribution properties developed under conditions of uniaxial tension are studied and analyzed for one AC mixture. It is shown that gage lengths of the order of the nominal maximum aggregate size measure a wide range of strain values: from zero strain up to 5 times the average strain. Moreover, as the gage length is increased, the scatter is reduced and the individual measurements yield values that are closer to their average. Subsequently, the confidence levels associated with using a limited number of gages with a given gage length are quantified. The results are then used to assess test protocol recommendations related to AC sample instrumentation. The size scale of the material's Representative Volume Element (RVE) is also addressed.

Comparison of Ultrasonic Pole Figures Based upon Ultrasonic Nondestructive Evaluation Method with Pole Figures Based upon Finite Element Polycrystal Model

The ultrasonic wave velocities in a polycrystalline aggregate are sensitively influenced by texture changes due to plastic deformation, and their relationship was systematically analyzed by Sayers [J. Phys. D: Appl. Phys. 15 (1982)]. According to Sayers's proposed model, it is possible to construct ultrasonic pole figures via the crystallite orientation distribution function (CODF), which can be derived by using ultrasonic wave velocity changes. In the previous paper, the theoretical modeling to simulate ultrasonic wave velocities propagating in solid materials under plastic deformation has been proposed by the authors and proved to be in good agreement with experimental results. In the present paper, the proposed theoretical modeling is applied to construct the ultrasonic pole figures based upon Sayers's model under various loading conditions of uniaxial tension, pure torsion, equi-biaxial tension-compression, biaxial compression and biaxial tension, respectively. To examine the accuracy and reliability of the ultrasonic pole figures simulated by the proposed theoretical modeling, the ultrasonic pole figures are compared with those analyzed by the finite element polycrystal model (FEPM). The results show a remarkable qualitative similarity among the two methods.

Serrated plastic deformation in LiF single crystals at high temperatures

The serrated plastic flow in LiF single crystals has been studied in the mode of active deformation at high temperatures (T = 573–1093 K). The parameters of the jumps in the deforming stresses (normalized amplitude and relaxation time of stress oscillations) were determined at the stage of strain softening under conditions of uniaxial compression and tension. It was shown that the jump parameters are essentially dependent on the type of the stressed state and the deformation temperature. The activation energy of serrated deformation in shear bands was established to be close to the migration energy for cation vacancies.

Stress Concentration near an Elastic Ellipsoidal Inclusion in an Infinite Body

The elastic problem is considered for a body containing an ellipsoidal inclusion under the conditions of uniaxial tension. The problem is reduced to the solution of a system of three integro-differential equations for the jumps of stresses and displacements on the surfaces of the inclusion. The exact solution of these equations is obtained and relations for the approximate evaluation of stresses in the matrix and inclusion are presented. Various special cases of the problem are analyzed and fairly simple formulas convenient for the engineering strength analysis of inhomogeneous bodies are deduced.

Tension and compression tests of two polymers under quasi-static and dynamic loading

Testing methods have been developed to determine the dynamic stress–strain responses and failure behavior of an epoxy, Epon 828/T-403, and a poly(methyl methacrylate) (PMMA) under high-strain-rate uniaxial tension and compression conditions. A split Hopkinson tension bar was modified for the dynamic tensile stress–strain behavior of the low-strength and low-mechanical-impedance specimens. An aluminum split Hopkinson pressure bar was used to determine the dynamic compressive responses. A pulse-shaping technique was employed in both dynamic tension and compression experiments to ensure that valid experimental conditions were satisfied. Results show that, compared with quasi-static behavior, dynamic tension causes smaller failure strains, whereas dynamic compression results in significantly higher compressive strengths for both materials.

The Effect of Silicon Addition on High-Temperature Tensile Deformation of Superplastic Yttrium Aluminum Garnet (YAG) Ceramics.

The effect of doping Silicon on the high-temperature deformation of superplastic Yttrium Aluminum Garnet (YS-YAG) was studied under conditions of uniaxial tension. In the preceding paper, the elongation and strain rate of YAG ceramics was described as having decreased by the addition of Si as a sintering aid. This was one of the reasons that the grain size of Si-doped YAG ceramics greatly increased compared with that of non-doped YAG ceramics during deformation. Creep deformation of Y2O3-excess YAG, with an average grain size of 1.6μm, was shown to have an elongation of over 210% (=en) at 1773 K. Accordingly, we prepared Si-doped Y2O3-excess YAG ceramics (YS-YAG) having the above two chemical composition, and developed YAG materials having two characteristics; remarkable grain growth and elongation. The deformation of YS-YAG reached 200% (=en) at 1773 K under a constant stress creep tensile test, in spite of the grain size of YS-YAG changed from 1.5 μm to 6μm during deformation.

Effect of Hot Deformation under Complex Loading on the Transformation of Lamellar Type Microstructure in Ti-6.5Al-3.5Mo-1.6Zr-0.27Si Alloy

The transformation of the lamellar type microstructure to an equiaxed one in two-phase titanium alloys is determined not only by temperature-strain rate regimes but also by the modes of loading. The experimental results of investigations relating to the influence of one- and two-component monotonous loading on microstructure and mechanical behavior of the two-phase Ti-6.5Al-3.5Mo-1.6Zr-0.27Si titanium alloy are presented in this work. It is shown that under conditions of proportional torsion + tension loading the transformation of the lamellar microstructure occurs more uniformly in the transverse section of a sample and over its length than under conditions of simple torsion or uniaxial tension. The transformation is accompanied by formation of a typical texture based on the strain state. The following uniaxial tension in optimal temperature-strain rate regimes of superplasticity is characterized by a lower value of flow stress, uniform distribution of deformation and further microstructure transformation within the whole sample volume.

Comparison of Ultrasonic Pole Figures Based Upon Ultrasonic Nondestructive Evaluation Method With Pole Figures Based Upon FEPM.

The ultrasonic wave velocities in a polycrystalline aggregate are sensitively influenced by texture changes due to plastic deformation, and their relationship was systematically analyzed by Sayers. According to Sayers's proposed model, it is possible to construct ultrasonic pole figures via the crystallite orientation distribution function (CODF), which can be derived by using ultrasonic wave velocity changes. In the previous paper, the Sayers's model was examined by experimental work and the effect of plastic deformation on texture development of an aluminum alloy specimen was studied by using ultrasonic pole figures as one of its applications. In the present paper, the ultrasonic pole figures based upon Sayers's model are constructed under various loading conditions of uniaxial tension, pure torsion, biaxial tension-compression, biaxial compression and biaxial tension, respectively. To examine its accuracy and reliability, the ultrasonic pole figures are compared with ones analyzed by the finite element polycrystal (FEPM), which has already been considered as a well-developed technology for the analysis of microstructural behaviors due to plastic deformation. The results show a remarkable qualitative similarity among the two methods.

Weld metal ductility in aluminum tailor welded blanks

The objective of the research described in this article was to characterize and numerically describe the ductility of weld material in aluminum tailor welded blanks under uniaxial tension conditions. Aluminum tailor welded blanks consist of multiple thickness and alloy sheet materials welded together into a single, variable thickness blank. To evaluate the mechanical properties of the weld material in these tailor welded blanks, a series of tensile specimens containing varying ratios of weld and monolithic material in the gage area of the specimen were tested. These experimental results show that increasing the amount of weld in the cross-sectional area of the specimen decreases the ductility of the specimen and that the weld characteristics have a pronounced impact on ductility. Using the experimental results and classical tensile instability and necking models, a numerical model was developed to describe the ductility of the weld metal. The model involves basic material properties and an initial imperfection level in both the weld and monolithic materials. The specimens studied were produced from 1- to 2-mm AA5182-O aluminum alloy sheet material welded into blanks using an autogenous gas tungsten arc welding process.

On Failure Modes and Strength Characterization of Brittle Disordered Materials under Uniaxial Compression and Tension

With a newly developed Material Failure Process Analysis code (MFPA(2D)), influence of hetero geneity on fracture processes and strength characterization of brittle disorder materials such as rock or concrete is numerically studied under uniaxial compression and tension conditions. It is found th at, due to the heterogeneity of the disordered material, relatively more diffused micro-fractures appear in the early stage of loading. Different from homogeneous materials such as glass, macro-crack nucleation starts well before the peak stress is reached and the crack propagation and coalescence can be traced, which can be taken as a precursory to predict the macro-fracture of the material. The presence of residual strength in the post-peak region and the resemblance in the stress-strain curves between tension and compression are significant results and are found to be dependent on the heterogeneity of the specimens. Examples showing the tentative applications of MFPA(2D) in modeling failure of composite materials and rock or civil engineering problem are also given in this paper.

The effect of defect introduction vs. load application sequencing on defect-induced stress distributions in steel samples

This study examines the effect of altering the sequence of defect introduction vs. load application on the defect-induced stress distributions in steel samples loaded under conditions of uniaxial tension. The stresses in the samples were measured using neutron diffraction and Magnetic Barkhausen Noise (MBN). In addition, the samples were scanned using Magnetic Flux Leakage (MFL) to determine the effect of sequencing on the MFL signal amplitude and trend with changing applied loads. At loads resulting in local plastic deformation at the defect edge, studies show distinct differences in the defect-induced stress distributions between through-holes milled prior to the application of load (pre-drilled), compared to those milled while the sample was held at-load (in situ). The consequences of these findings are discussed in light of MFL tool calibration and the subsequent determination of the Maximum Allowable Operating Pressure (MAOP) for in-service pipelines. The implications with regards to the hole-drilling technique for stress measurement are also discussed.

Influence ff the initial state on the strength of pressed lithium hydride

We present the results of mechanical testing of pressed lithium hydride under the conditions of uniaxial compression, radial compression, and bending. The specimens were made of three different powder fractions. Their density varied depending on the level of compacting pressure. It is shown that, in the investigated range of parameters characterizing the initial state of the material, the dependences of strength on the characteristic size of the original powder d and the density of the material of the specimen ρ can be described by the same formula of the form σf=σ0-klog(d/d0)+l(ρ-ρ0), where d0 and ρ0 are arbitrarily chosen reference points, and σ0, k, and l are coefficients determined by the method of regression analysis. The use of data on the strength of pressed lithium hydride under the conditions of uniaxial and radial tension processed as indicated above enabled us to obtain a similar dependence for the conditions of uniaxial tension.

An Experimental Study of Low Velocity Impact Damage in Woven Fiber Composites

A study is made on the low velocity impact response and post-impact mechanical capacity of woven fiber [0/90,-45/45,0/90]s carbon epoxy composite plates. This complements the work done by numerous other researchers who have also examined low velocity impact of composites, but have focused on unidirectional, cross-ply or quasi-isotropic laminates. In the present study, post-impact static uniaxial tension, compression, as well as tension-compression fatigue tests are performed. The damage mechanisms for woven laminates are found to be predominantly delamination and fiber breakage, with the area of impact-induced delamination increasing linearly with impact energy for the range of energies examined. Damage extent and type are also dependent on the curvature of the impactor tip and deformation generated by a sharp impactor is more localized. The existence of a threshold energy level below which no delamination discernible by C-scan occurs is noted. In contrast with previous findings, it is observed that the peak in the impactor deceleration-time response is not associated with the onset of fiber failure, which can occur earlier. The amount of energy absorbed when this peak occurs therefore does not indicate the energy required to initiate fiber breakage. It is observed that residual tensile strength is a function of delamination area and impactor tip radius. For static compression and tension-compression fatigue, the residual load-bearing capacity is only dependent on delamination area. Under compression, delamination promotes the micro-buckling of fibers, whereas in tension, failure is predominantly via fiber breakage. For a common impact energy and impactor, a damaged specimen is weaker in compression than in tension.

Strength and Fracture of SPKh18N9T Steel and SP36KNM Alloy under Dynamic Loading

We present results of an experimental investigation of the strength properties of SPKh18N9T steel and SP36KNM alloy and the characteristics of fracture processes in these materials under dynamic loading. It is shown that, under conditions of uniaxial static tension, the standard mechanical characteristics of these materials are very close to each other. Moreover, as the strain rate increases to 103 sec−1, they undergo slight changes (thus, the yield limit and the ultimate strength increase by at most 13% and 6%, respectively, and the relative elongation at rupture decreases by 5%). At the same time, under impact loading, the impact strength of SPKh18N9T steel is twice that exhibited by SP36KNM alloy. This fact can be partially explained by the difference in the initial porosities of these materials.

Effect of a difference between the elasticity characteristics of the base and the coating on the stress-strain state of a composition. Part 3. Distribution of tangential and normal stresses in the coating

We present expressions for numerical evaluation of normal stresses in coatings and tangential stresses in the plane of adhesive contact formed under conditions of uniaxial tension of the base. These expressions take into account the difference between the Poisson ratios of the coating and the base. The indicated stresses are functions of the level of strains in the base and elastic and geometric characteristics of the base and the coating. We present plots of distributions of stresses in the plane of adhesive contact for gas-thermal coatings. The influence of fields of additional stresses must be taken into account in strength analysis of products with coatings and in experimental evaluation of the mechanical characteristics of base-coating compositions.

Characteristics of grain boundary migration and sliding during fatigue of high purity lead

Samples of high purity Pb were tested under conditions of low cycle reverse bending fatigue at a high homologous temperature. Inspection showed that the grain boundaries migrate in a regular and cyclic manner and, under conditions of constant frequency and strain amplitude, the average amounts of migration, m̄, and sliding, v̄, both increase with the number of loading cycles, N. If N is maintained constant, the values of m̄ and v̄ increase with increasing strain amplitude. Grain boundary cracking was observed after testing through 25 cycles at the higher strain amplitudes. These results confirm that the formation of intercrystalline cracks and cavities occurs more easily in cyclic loading than under conditions of uniaxial tension.

Effect of testing atmosphere on low cycle fatigue of hot work tool steel at elevated temperature : Tsuhii, N., Abe, G., Fukaura, K. and Sunada, H. ISIJ Inn. (1995) 35 (7), 920–926

The influence of an aggressive environment (0.6 M, aerated NaCl solution) on short fatigue crack initiation and growth behaviour has been studied. The study involved three major test series, namely: air fatigue, corrosion fatigue, and intermittent air fatigue/corrosion fatigue. The above tests carried out under fully reversed torsional loading conditions at a frequency of 5 Hz, showed that it was the non-metallic inclusions which took part in crack initiation resulting from debonding at metal matrix/inclusion interface and pitting of inclusions in both air and corrosove environments, respectively. Short fatigue crack growth results in these two environments obtained by using plastic replication technique, indicated a large effect of microstructure i.e. prior austenite grain boundaries. The stage/stages at which the environmental contribution was dominant has been discussed by considering the results achieved from intermittent tests. However, the mechanisms involved in corrosion fatigue short crack growth have also been described in the light of results obtained from futher investigations carried out by conducting corrosion fatigue tests under applied cathodic potential conditions and tests on hydrogen pre-charged specimens under air fatigue and uniaxial tension conditions.