Axial Tensile Tests Research Articles

EVALUATION OF THE HOOP TENSILE PROPERTIES OF A STEAM GENERATOR TUBE

The steam generators in a pressurized water reactor (PWR) are large heat exchangers that use the heat from the primary reactor coolant to make steam on the secondary-side to drive turbine generators. Hoop stress is known to be the main cause of fracture of inner pressurized tubes such as the steam generator tube. However, because the steam generator tube is too small to be manufactured to a standard tensile specimen in the hoop direction, the axial tensile properties of the steam generator tube (or original material properties) instead of hoop tensile properties have been used to estimate the fracture properties of a steam generator tube. In this study, we have conducted not only axial tensile tests but also ring tensile tests. From these test, both the axial and hoop tensile properties of steam generator tubes were obtained, and the reliability of the hoop tensile properties were confirmed by burst test of a real steam generator tube.

Technique to Assess Aging of Propellant Grain

Physical properties of composite propellants used in solid rocket motors change significantly with age. To predict the margin of safety and to reevaluate the remaining service life, the structural integrity analysis of solid propellant grains of aged rocket motors is pa-formed at various stages of their life span. To have the reliable results from these analyses, it is mandatory to use the current physical properties of the propellant at the time of analysis. Change in physical properties due to aging is more significant at exposed surfaces. Traditional methods of assessing current physical properties may not truly represent the properties of the batch. The paper presents a novel technique to measure the stress strain response at the exposed surface of propellant grain using a miniature testing device. This specially designed device is able to measure the stress response while the propellant surface is compressed at a constant rate. This measured stress strain behavior is then co related with the physical properties measured by routine tensile tests of the similar type of propellant which is aged artificially. It is observed that there exists an excellent correlation between the measured stress values by the sensor and physical properties measured by uni axial tensile test. This nondestructive technique provides properties of propellant grains of all the motors in the batch comprehensively. The technique is safe as well as economical as compared to the traditional methods.

Mechanical Characterization of Anisotropic Planar Biological Soft Tissues Using Large Indentation: A Computational Feasibility Study

Traditionally, the complex mechanical behavior of planar soft biological tissues is characterized by (multi)axial tensile testing. While uniaxial tests do not provide sufficient information for a full characterization of the material anisotropy, biaxial tensile tests are difficult to perform and tethering effects limit the analyses to a small central portion of the test sample. In both cases, determination of local mechanical properties is not trivial. Local mechanical characterization may be performed by indentation testing. Conventional indentation tests, however, often assume linear elastic and isotropic material properties, and therefore these tests are of limited use in characterizing the nonlinear, anisotropic material behavior typical for planar soft biological tissues. In this study, a spherical indentation experiment assuming large deformations is proposed. A finite element model of the aortic valve leaflet demonstrates that combining force and deformation gradient data, one single indentation test provides sufficient information to characterize the local material behavior. Parameter estimation is used to fit the computational model to simulated experimental data. The aortic valve leaflet is chosen as a typical example. However, the proposed method is expected to apply for the mechanical characterization of planar soft biological materials in general.

Plastic Deformation of Irradiated Zirconium Alloys: TEM Investigations and Micro-Mechanical Modeling

Abstract TEM investigations have been performed on irradiated samples after deformation covering various testing conditions for different recrystallized Zr alloys. It is shown that for transverse tensile tests and internal pressure tests performed at 350°C, only basal channels are observed for strain levels up to uniform elongation, whereas only prismatic and pyramidal channels are observed for axial tensile test. Then, focusing on internal pressure testing, irradiation hardening and strain hardening behavior have been analyzed in detail and compared to TEM observations. It is proposed that dislocation channeling phenomenon leads to high strain incompatibility between channels and surrounding grains and therefore to high microscopic internal stresses. These high microscopic internal stresses are believed to induce strong kinematic hardening at the macroscopic scale, as suggested by the mechanical behavior analysis. Finally, a micro-mechanical model based on microscopic deformation mechanisms and using homogenization techniques is proposed, taking into account the observed channeling phenomenon.

Acoustic emission study and strength analysis of crimped steel-composite joints under traction

Integrated in composite electrical insulators, metal/fibreglass-reinforced-plastic (GRP) joints made of an epoxy rod reinforced with E-glass fibres and of two crimped steel end-fittings are investigated numerically and experimentally. Numerical stress and strain distributions through the bond during the crimping phase and under an axial tensile test are calculated with a solid 3D finite element model and the damage initiation in the composite is highlighted. The simulations are compared to experimental data obtained from several joint specimens tested under pulling on an experimental set-up equipped with strain gauges and an acoustic emission system. Good correlation between the finite element predictions and the test results is found. The numerical and experimental study is also completed with a sensitivity analysis of the main geometrical parameters of the joints.

Mechanical Properties of Zircaloy-4 PWR Fuel Cladding with Burnup 54-64MWd/kgU and Implications for RIA Behavior

Abstract The PROMETRA material testing program is a support program related to the study of high burnup fuel rod behavior under Reactivity Initiated Accidents (RIA) and to the interpretation of the CABRI REP-Na RIA test results. Hoop and axial tensile tests have been performed on fresh and irradiated Zircaloy-4 cladding alloy first at CEA Grenoble hot labs and now at CEA Saclay in order to assess the cladding mechanical behavior during RIA transients. Efforts have been continuously carried out in order to improve the prototipicallity of the tests for RIA studies involving new specimens and new testing techniques. The corrosion level of irradiated specimens reached up to 130 μm of oxide layer thickness. The influence of in-pile oxide layer spallation has also been addressed. High strain-rate material properties of irradiated Zircaloy-4 and the consequences of hydride embrittlement can be derived from the PROMETRA program.

Mechanical properties of YBaCuO formed on Ni-based alloy substrates with IBAD buffer layers

Mechanical properties of YBaCuO superconducting tape produced by a multi-stage metal-organic chemical vapor deposition (MOCVD) technique have been investigated. It is important for YBaCuO superconducting tape to tolerate stress strain and maintain flexibility in order to be used for electric power applications, magnetic applications, and so on. At this time, we have produced an approximately 0.25 /spl mu/m YBaCuO layer on a pulse laser deposition (PLD)-CeO/sub 2//ion beam assisted (IBAD)-Gd/sub 2/Zr/sub 2/O/sub 7//Ni-based alloy substrate by an MOCVD technique, and approximately 4 /spl mu/m Ag was sputtered on it as a protective layer. The thickness of each layer was approximately 1.0 /spl mu/m, 1.0 /spl mu/m and 0.1 mm respectively. Its critical current was about 50 A. The mechanical properties of YBaCuO tape formed on Ni-based alloy substrates with a CeO/sub 2//Gd/sub 2/Zr/sub 2/O/sub 7/ buffer layer will be described. Tensile or compressive bend stress tests were conducted, and normalized critical current and the value n were evaluated. The degradation of its critical current was confirmed not to be in the big problem level in manufacturing applications. In addition, the surfaces of YBaCuO layers were observed by scanning electron microscopy and no crack was observed on them. Next, axial tensile stress tests were conducted and the YBaCuO tape was compared with biaxially textured Ni-3at.%W alloy substrates and YBaCuO layers on Ag substrates. Axial tensile stress characteristics of the YBaCuO tape were confirmed to be much higher than others. The YBaCuO tape was confirmed to have adequate axial tensile stress characteristics for designing a coil which can tolerate electromagnetic force.

A statistical TEM investigation of dislocation channeling mechanism in neutron irradiated zirconium alloys

Plastic deformation in irradiated zirconium alloys occurs in a very heterogeneous manner at the grain scale by the clearing up of radiation-induced prismatic loops by gliding dislocations and the channeling of these dislocations inside narrow bands of the grain. A statistical TEM investigation of this mechanism has been performed on neutron irradiated recrystallized Zr alloys tested at 350 °C. Due to the strong anisotropy of plastic deformation, different loading conditions have been investigated. It is shown that for transverse tensile tests and closed end burst tests, only basal channels are observed, whereas for axial tensile tests, prismatic and pyramidal channels are observed. This phenomenon can be understood in terms of texture and interactions between dislocations and irradiation induced loops. From Schmid factor calculations, we have also been able to prove that irradiation leads to a higher increase of critical resolved shear stresses for prismatic and pyramidal slip systems than for basal slip system.

Characterizing steel tube for hydroforming applications

With the increased use of tubular steel products, especially for hydroforming applications, it is important to be able to predict the performance of tube from sheet tensile tests. In the present study, two aluminum killed draw quality (AKDQ) steels and one high strength low alloy (HSLA) steel were evaluated. Tensile properties and plastic strain ratios were measured on sheet material in the longitudinal and transverse directions. Axial tensile tests were performed on material extracted from production tubes. Material from quasi tubes, which are strip material bent to the same curvature as the tubes but not welded or sized, was also tested. Residual stresses in the production and quasi tube were determined by displacement methods. A hydraulic burst test was performed on the production tubes to simulate a hydroforming operation. Effective strains resulting from tubemaking are calculated for two discrete operations: bending and sizing. For the production tubes, a linear relationship was found between a load factor (strength times thickness) and effective sizing strain. The relationship between load factor and residual stress was also linear. Predictions of the maximum pressure and the strain at instability during a hydraulic burst test are shown to compare favorably with experimental values, based on flat sheet properties and tubemaking strains. The prediction of the yield strength in the tube based on flat sheet properties is shown to be fairly accurate when the effective sizing strain is small compared to the effective bending strain.

Geometric and mechanical properties of human cervical spine ligaments.

This study characterized the geometry and mechanical properties of the cervical ligaments from C2-T1 levels. The lengths and cross-sectional areas of the anterior longitudinal ligament, posterior longitudinal ligament, joint capsules, ligamentum flavum, and interspinous ligament were determined from eight human cadavers using cryomicrotomy images. The geometry was defined based on spinal anatomy and its potential use in complex mathematical models. The biomechanical force-deflection, stiffness, energy, stress, and strain data were obtained from 25 cadavers using in situ axial tensile tests. Data were grouped into middle (C2-C5) and lower (C5-T1) cervical levels. Both the geometric length and area of cross section, and the biomechanical properties including the stiffness, stress, strain, energy, and Young's modulus, were presented for each of the five ligaments. In both groups, joint capsules and ligamentum flavum exhibited the highest cross-sectional area (p < 0.005), while the longitudinal ligaments had the highest length measurements. Although not reaching statistical significance, for all ligaments, cross-sectional areas were higher in the C5-T1 than in the C2-C5 group; and lengths were higher in the C2-C5 than in the C5-T1 group with the exception of the flavum (Table 1 in the main text). Force-deflection characteristics (plots) are provided for all ligaments in both groups. Failure strains were higher for the ligaments of the posterior (interspinous ligament, joint capsules, and ligamentum flavum) than the anterior complex (anterior and posterior longitudinal ligaments) in both groups. In contrast, the failure stress and Young's modulus were higher for the anterior and posterior longitudinal ligaments compared to the ligaments of the posterior complex in the two groups. However, similar tendencies in the structural responses (stiffness, energy) were not found in both groups. Researchers attempting to incorporate these data into stress-analysis models can choose the specific parameter(s) based on the complexity of the model used to study the biomechanical behavior of the human cervical spine.

Study on surface- and mechanical fiber characteristics and their effect on epoxy composite properties tuned by continuous anodic carbon fiber oxidation

Continuous anodic oxidation was employed to alter the surface chemical properties of carbon fibers. As expected, the wetting behavior by water improved and that of non-polar liquid diiodomethane deteriorated. The calculated surface tensions mirror the changes in the physicochemical surface properties. The zeta (ζ)-potential measurements performed also reflect changes in the surface chemistry of the investigated carbon fibers. A correlation between the measured ζ-potentials and the wetting behavior of water on anodically oxidized carbon fibers was found. The influence of anodic carbon fiber oxidation on the epoxy composite properties was studied by a modified axial tensile test, which allows additionally the measurement of the so-called 'notching force' as a measure of the interfacial composite properties. Common model-composite samples were used to check the reliability of this test. The determined 'notching force' as a measure of adhesion correlates with the increased polar component of the fiber surface tension.

ＧＦＲＰ板の塑性加工性と繊維間摩擦との関係

The deformation characteristics of metallic materials under the single axial tensile testing are analyzed by an upper bound method based on the theorem of plasticity using R. Hill's orthogonal anisotropic yield criterion. This method was applied to estimate the deformation behavior of a GFRP sheet, combining the r-value as an estimate of plastic workability on orthogonal anisotropic metallic materials. The difference in strength between woven and laminated sheets is considered to be caused by the fiber to fiber friction, and this is calculated on a woven sheet using a unit model. Measuring the orientation angle and the elongation of fiber, the relation between the r-value and fiber orientation was evaluated.It was concluded that these concepts can be effectively applied to the estimation of plastic workability.

Mechanical Test Methods for Biomedical Membranes

It is important to estimate the mechanical characteristics and strength of biomedical membrane. For this purpose, previously we have proposed several mechanical test methods for biomedical membranes. To establish the safety design for biomedical membrane, such as cellophane membrane for hemodialysis, it is important to estimate the viscoelastic characteristics of these materials. On the other hand, artificial biomedical membrane such as tympanic membrane, are subjected to noncontact internal air pressure under the membranous state. To estimate mechanical characteristics of such membrane, it is necessary to develop a well-simulated test under the gaseous pressure and the other mechanical test under the membranous state. In this paper, several test methods for these purposes were shown. Furthermore, results obtained by these methods were shown and related to clinical problems. These proposed test methods are quite different from the axial tensile test. But they are also important to estimate the mechanical property of biomedical membrane. Each result obtained by these test methods has its own significance. By selection of the most suitable test method for each purpose and revealing these mutual relations, safety design of artificial organs can be performed from the viewpoint of the strength.

Effect of Strain Hold Time on Fatigue Life of Alloy 800H at High Temperatures.

Axial strain-controlled fatigue tests and tensile peak strain hold fatigue tests were conducted on alloy 800H in 850°C∼950°C air to investigate the effect of the stress relaxation process on the fatigue life of the material. Subsequently, it was noted that the fatigue lives were only slightly affected by temperature in this high temperature region. It was also recognized that fatigue life decreased with the introduction of tensile strain hold time, but the effect of strain hold time on fatigue life saturated in a rather short strain hold period due to the rapid stress relaxation behavior of the material in these temperatures. These results were investigated from the viewpoint of microstructural changes and fractographic features of specimens. Finally, creep-fatigue damage interaction values were calculated and D=0.4 was found to be the optimum minimum damage value of this material.

Effect of Tablet Lubricants on Axial and Radial Work of Failure

AbstractDuring diametral compression and axial tensile strength testing force-displacement curves were obtained for tablets of microcrystalline cellulose. The area under the curve, termed work of failure, was determined by planimetry. For each of the five lubricants studied as the concentration of the lubricant was increased in the tablet, the work of failure was considerably less. The effect was especially marked in the axial plane.

Influence of structure on the resistance of 65G steel to fatigue crack growth

(230-mm diameter) with a center crack, rectangular (width 25 mm) with an edge crack for axial tensile testing, and rectangular compact (width 81 mm) for off-center tensile testing~ The line of action of the forces always coincided with the rolling direction and the through crack developed perpendicular to it. To obtain different structures, the disk samples were normalized or hardened in oil from 810~ and tempered at 180, 320, 380, 440 and 5800C. After heat treatment the samples were ground to a thickness of 3 mm. Data on the microstructure and the mechanical properties in short-term static tension of standard flat samples is shown on Table i. To study crack growth in steel of a given structure from one to four samples were used and in individual cases up to seven rectangular samples, which were cut from test disks. The tests were made using the known method [2, 3] in a machine with an inertial load exciter [4] in laboratory air with a relative humidity of 40-60% using an almost from-zero (R = 0.05) sinusoidal tensile cycle with a loading frequency of 16-20 Hz and at high crack growth rate (more than i0-6 m/cycle), because of the difficulty in measuring its length, also at a frequency of 0.017 Hz on a machine with rigid loading [5]. In the i0"-i0 -" m/cycles range of rates the tests were repeated at the two frequencies in order to be convinced of their weak influence on the results. The rate of development of the original crack in growth of it to an initial length of 2 mm from an initiating notch was always greater than 10-9 m/cycle despite the low loads and the use of various methods easing origin of it [6]. Therefore, for investigations of crack resistance at lower rates the load was reduced in steps with observance of existing recommendations [2, 7]. The sample was tested in stages during which all parameters of the load cycle were maintained constant. In each stage the range of the stress intensity factor ~K = KmaX-Kminin the disk samples was constant if the crack length did not exceed 95 mm and in the remalning cases increased with crack length. The rate of crack development v in the stages with a constant AK was calculated from five to eight successive measurements of its length using the method of least squares [2] while with an increasing AK the value of v was determined as the ratio of the increase in the crack between two successive measurements to the corresondlng number of cycles. For determination of the characteristics of cyclic crack resistance and an analytical description of the full fatigue failure curves, use was made of the equation [8]