Showing papers on "Tensile testing published in 1987"

Experimental Characterization of Advanced Composite Materials

Abstract: INTRODUCTION Background Laminate Orientation Code Influences of Material Orthotropy on Experimental Characterization Typical Unidirectional Composite Properties References ANALYSIS OF COMPOSITE MATERIALS Constitutive Relations Micromechanics Laminated Plate Theory St. Venant's Principle and End Effects in Composites Lamina Strength Analysis Laminate Strength Analysis Fracture Mechanics Concepts Strength of Composite Laminates Containing Holes References PROCESSING OF COMPOSITE LAMINATES Processing of Thermoset Composites Autoclave Processing of Thermoplastic Composites Determination of Volume Fractions of Fibers, Resin and Voids References TEST SPECIMEN PREPARATION, TEST EQUIPMENT, STRAIN AND DEFORMATION MEASUREMENTS Cutting the Composite Laminate Tabbing Materials Tab Bonding Suggested Tab Bonding Procedures Hinge Attachment for DCB and MMB Specimens Specimen Conditioning Strain and Displacement Measurements Testing Machines References LAMINA TENSILE RESPONSE The Need for Lamina Testing Introduction to Tensile Testing Primary Concerns Specimen Configurations and Test Procedures Data Reduction References LAMINA COMPRESSIVE RESPONSE Shear-Loading Test Methods End-Loading Test Methods Combined Loading Compression (CLC) Test Methods Compression Test Procedures Failure Modes General Data Reduction Backing out Unidirectional Lamina Strength from a Test of a Cross-Ply Laminate Summary of Compression Test Methods References LAMINA SHEAR RESPONSE Iosipescu Shear Test Method (ASTM D 5379) Two-Rail Shear Test Method (ASTM D 4255) Three-Rail Shear Test Method (ASTM D 4255) [+-45]ns Tension Shear Test Method (ASTM D 3518) Short Beam Shear Test Method (ASTM D 2344) Summary References LAMINA FLEXURAL RESPONSE Testing Configuration Three-Versus Four-Point Loading Specimen Preparation and Flexural Test Procedures Data Reduction References LAMINA OFF-AXIS TENSILE RESPONSE Deformation and Stress in Unconstrained Specimens Influence of End Constraint Off-Axis Tensile Strength Test Procedure Data Reduction References LAMINA THERMOELASTIC RESPONSE Temperature Gage Sensing System Temperature Compensation Measurement of Thermal Expansion Data Reduction References LAMINATE MECHANICAL RESPONSE Data Reduction for Stiffness Properties Laminate Strength Analysis Test Specimen Preparation Test Procedures Data Reduction Example of a Typical Analysis: Axial Tensile Response of a Laminate References LAMINATE THERMOELASTIC RESPONSE Preparation of Test Specimens and Measurement of Thermal Expansion Data Reduction Analysis of Thermoelastic Response References OPEN-HOLE TENSILE AND COMPRESSIVE STRENGTHS OF LAMINATES Point and Average Stress Criteria Test Specimen Preparation Tensile Test Procedure and Data Reduction Standardized Open-Hole Tension Test Method Standardized Open-Hole Compression Test Methods References CHARACTERIZATION OF DELAMINATION FAILURE Double Cantilever Beam (DCB) Test End-Notched Flexure (ENF) Test Four-Point Bend ENF (4ENF) Test Mixed-Mode Bending (MMB) Test Edge-Cracked Torsion (ECT) Test References Appendix A: Compliance and Stiffness Transformations and Matrix Operations Appendix B: Preparation of Panels and Test Specimens Appendix C: Sample Laboratory Report Appendix D: Unit Conversions Index

Tensile Failure of Steel Fiber‐Reinforced Mortar

Abstract: Results are discussed from experimental and theoretical studies on the tensile failure of short, steel fiber-reinforced mortar/concrete SFRC composites. A displacement-controlled test method for conducting stable fracture tests on tension-weak brittle materials developed in an earlier study has been used for conducting uniaxial tension tests. Several concrete, mortar, paste, and SFRC mixes were tested. Fracture of SFRC in tension is observed to be influenced largely by the matrix softening behavior, the fiber-matrix interfacial response, and its composition parameters. The theoretical model proposed for the idealized SFRC composite takes into account these two primary nonlinear aspects of the failure mechanism in such composites, i.e., (1) the inelastic behavior of the fiber-matrix interface, and (2) the softening characteristics of the matrix. The model, in addition, is realistically sensitive to the reinforcement parameters like fiber volume content, aspect ratio, and the elastic properties of the fiber.

The tensile strength of the lithosphere and the localization of extension

Abstract: Summary Continents appear to rift in preference to oceans. Furthermore, some areas of continents appear to be more susceptible to rifting than others. Experimental rock mechanics data are used to estimate lithospheric strength for lithospheres of different structure, thereby to investigate the possible causes of rift localization. Using optimum creep parameters for silicic, mafic and ultramafic rocks, we find that lithospheric strength is inversely related to both crustal thickness and heat flow. By virtue of its thinner crust, oceanic lithosphere is inherently stronger than continental lithosphere. We find that oceanic lithosphere older than about 10 Ma should be able to withstand the lithospheric forces exerted on it by gravity sliding and plate interactions. Rifting or ridge-jumps are therefore only likely to occur in very young oceanic lithosphere. Low heat flow continental shields should also be able to withstand likely lithospheric forces without significant deformation. As the heat flow increases, however, the lithosphere is weakened dramatically. A smaller amount of weakening is associated with crustal thickening. Thus, unless rifting is localized by a strongly heterogeneous stress field, it will be by anomalously weak lithosphere. This lithosphere is likely to have anomalously high heat flow and/or crustal thickness prior to extension.

An experimental study of synthetic fibre reinforced cementitious composites

Abstract: Fibre reinforcement is one of the effective ways of improving the properties of concrete. However, current studios on fibre -reinforced concrete (FRC) have focused mainly on reinforcements with steel and glass fibres. Thin paper reports on an experimental programme on the properties of various synthetic fibre reinforced cementitious composites and the properties of the reinforcing fibres. Acrylic, polyester, and aramid fibres were tested in uniaxial tension, both in their original state as we!! as after ageing in nerO*nL Samples of these fibres were found to lose varying amounts of strength with time, depending on the ageing temperature. Two different test methods were used to measure the fibre-cement interfacial bond strength. The tensile properties of concrete reinforced with acrylic, nylon, and aramid fibres, in the form of random distribution or unioxial alignment, were studied by means of three different tests: compact tension, flexural, and splitting tensile tests. The properties of concrete, particularly that of apparent ductility, were found to be greatly improved by the inclusion of such fibre reinforcement.

Mechanical behavior of aluminum-lithium alloys at cryogenic temperatures

Abstract: The cryogenic mechanical properties of aluminum-lithium alloys are of interest because these alloys are attractive candidate materials for cryogenic tankage. Previous work indicates that the strength-toughness relationship for alloy 2090-T81 (Al-2.7Cu-2.2Li-0.12Zr by weight) improves significantly as temperature decreases. The subject of this investigation is the mechanism of this improvement. Deformation behavior was studied since the fracture morphology did not change with temperature. Tensile failures in 2090-T81 and -T4 occur at plastic instability. In contrast, in the binary aluminum-lithium alloy studied here they occur well before plastic instability. For all three materials, the strain hardening rate in the longitudinal direction increases as temperature decreases. This increase is associated with an improvement in tensile elongation at low temperatures. In alloy 2090-T4, these results correlate with a decrease in planar slip at low temperatures. The improved toughness at low temperatures is believed to be due to increased stable deformation prior to fracture.

A Methodology for Accurate Shear Characterization of Unidirectional Composites

Abstract: A combined experimental-analytical methodology is presented for accurate determina tion of the intralaminar shear modulus G 12 of unidirectional composites using the off-axis tension test and/or the Iosipescu test. It is demonstrated that consistent values of G 12 can be obtained with the two methods provided that: (1) specimen geometry is optimized for the off-axis test, (2) correction factors are employed to account for the shear stress nonuni formity in the test section of Iosipescu specimens. The problem of measuring the shear strength with these specimens is discussed. The 45-deg off-axis tensile coupon is recom mended for determination of the shear modulus. The 0-deg Iosipescu specimen is recom mended for determining an upper lower bound on the shear strength.

Erosion of unfilled elastomers by solid particle impact

Abstract: The response has been studied of eight unfilled elastomers (four natural rubber compounds, epoxidized natural rubber ENR50, butyl rubber, polybutadiene and polyurethane) to erosion by 150 μm silica sand at an impact velocity of 48 m sec−1. All were tested at an impact angle of 30°, close to the impact conditions occurring in pipe bends, while two were also tested at 90°. Wide variations in erosion rate were observed between different rubbers. These differences did not correlate systematically with the nature of the base elastomer, glass transition temperature or mechanical properties such as hardness, tensile strength or ultimate tensile elongation, nor with resistance to abrasive wear. Good correlation was, however, found with rebound resilience. A high resilience tended to imply high erosion resistance, The erosion rate was found empirically to be proportional to the quantity (1 - fractional resilience) raised to the power 1.4. Different surface morphologies were found in specimens of high and low resilience after erosion at 30°. Finely spaced transverse ridges formed on high-resilience rubbers, whereas surface features on low-resilience rubbers showed no directionality. Preliminary conclusions are drawn about possible mechanisms of material removal.

Failure Stress Criteria for Composite Resin

Abstract: In previous work (Peters and Poort, 1983), the stress distribution in axisymmetric models of restored teeth was analyzed by finite element analysis (FEA). To compare the tri-axial stress state at different sites, they calculated the Von Mises equivalent stress and used it as an indication for weak sites. However, the use of Von Mises' theory for material failure requires that the compressive and tensile strengths be equal, whereas for composite resin the compressive strength values are, on the average, eight times larger than the tensile strength values. The objective of this study was to investigate the applicability of a modified Von Mises and the Drucker-Prager criterion to describe mechanical failure of composite resin. In these criteria, the difference between compressive and tensile strength is accounted for. The stress criteria applied to an uni-axial tensile stress state are compared with those applied to a tri-axial tensile stress state. The uni-axial state is obtained in a Rectangular Bar (RB) specimen and the tri-axial state in a Single-edge Notched Bend (SENB) specimen with a chevron notch at midspan. Both types of specimens, made of light-cured composite, were fractured in a three-point bend test. The size of the specimens was limited to 16 mm x 2 mm x 2 mm (span, 12 mm). Load-deflection curves were recorded and used for linear elastic FEA. The results showed that the Drucker-Prager criterion is a more suitable criterion for describing failure of composite resins due to multi-axial stress states than are the Von Mises criterion and the modified Von Mises criterion.

Microstructures and mechanical properties of Ni 3 Al alloyed with iron additions

Abstract: The alloying behavior of iron in B-doped Ni3Al was studied using optical and transmission electron microscopy for microstructural analysis and tensile testing for mechanical property evaluation. The aluminide dissolves less than 15 at. pct iron. At iron levels of 15 pct, depending on the aluminum level, formation of both transformed B2 phase (β′) and disordered fee phase (γ) is observed. The phase relationships in the aluminide containing 10 pct iron were studied in detail by quenching from temperatures below 1370 °C. Tensile properties of nickel-iron aluminides were determined as functions of iron content and test temperature. The tensile results are discussed in terms of solid-solution hardening, atomic size misfit, and precipitation of γ, β′, and carbides.

A new end tab design for off-axis tension test of composite materials

Abstract: A new end tab fabricated using a fiberglass knit in a silicon rubber matrix was used for off-axis tension tests on unidirectional composites. It was shown experimentally that this new tab allowed shear deformation of the specimen to occur in the hydraulic grips and, thus, produce a uniform state of strain in the specimen. Consequently, the shear modulus could be determined accurately using this new tab. Furthermore, due to the absence of stress concentrations, this procedure could also be used to determine shear strength.

The yield behaviour of amorphous polyethylene terephthalate: an activated rate theory approach

Abstract: Yield-stress measurements on amorphous polyethylene terephthalate film are presented covering five decades of strain rate at temperatures from just below the glass transition (≈ 60° C) to −160° C. The data were obtained by combining measurements from a conventional Instron machine with data from a high-speed tensile tester capable of applying strain rates of up to 50 sec−1. Five different failure modes have been identified over this extensive range of test conditions. All data from tests which show a clear yield point can be described accurately by an extension of the Ree Eyring approach to include two processes. The process which is only important at low temperatures correlates well with theβ-process observed in dynamic mechanical experiments.

Rheological properties of linear low density polyethylene/polypropylene blends. Part 2: Solid state behavior

Abstract: This second paper of a series continues the examination of the tensile properties of two series of linear low density polyethylene/polypropylene, (LLDPE/PP) blends. The blends were prepared using a twin-screw extruder and cover the whole concentration range, An Instron Universal Tensile Tester was used to measure the tensile properties of the blends between 10 and 70°C, and the temperature and composition dependences of the modulus were examined. A comparison is established between the solid state and melt properties to underline the behavior in the PP rich region. Results of dynamic mechanical experiments and differential scanning calorimetry on the same materials are also given, and the mechanical behavior is discussed in terms of the variation of the system's crystallinity.

A simplified model of heat generation during the uniaxial tensile test

Abstract: The temperature rise in a sheet tensile specimen has been calculated by the finite difference method for a plain-carbon steel at various strain rates and in several environments. Prior to necking, a uniform heat generation function is used with the governing flow equation while during the post-uniform strain, an empirical heat generation function is used. The empirical function is based on a strain distribution equation generated by curve fitting of experimental data. The effect of heat transfer conditions on the temperature increase has been discussed. The maximum temperature rise in air may reach 42 K at the center of an I.F. steel specimen at a strain rate of 10-2/s. The instability strain during tensile testing has been predicted by taking into account strain hardening, strain-rate hardening, and deformationinduced heating. The results show that significant deformation heating can occur during tensile testing in air at “normal” strain rates near 10-2/s, and that the uniform elongation can be affected markedly. Predictions for other alloys based on tabulated data are also presented.

Microcracking of concrete under compression and its influence on tensile strength

Abstract: A new parameter representing damage of concrete due to compressive stresses is investigated. Very important tensile strength losses are obtained after compressive loading over 40% of the compressive strength. Microcracking of concrete takes place under such load leading to tensile strength losses depending also on time under load, water content and type of aggregate. Under maximum compressive load a tensile strength reduction of about 50% is obtained.

Some experimental results on yield condition in plane stress state

Abstract: In the present paper, the determination of yield locus curves for deep drawing sheet metal is described. The experiments are based on the combination of biaxial tension tests on plane cross-shaped specimens with uniaxial tension and compression tests performed on conventional specimens. The influence of preloading (prestrain) on the hardening behaviour is discussed. The material coefficients are computed through the equalization of the test results by means of a quadratic formulation of the yield condition. Finally, the material coefficients are given as functions of the prestrain of specimens in the rolling direction.

Effect of coatings on oxidation of Ti-6Al-2Sn-4Zr-2Mo foil

Abstract: The viability of using coated Ti-6Al-2Sn-4Zr-2Mo foils at 620°C in air was established through mechanical and thermogravimetric testing. Weight-grained and oxygen embrittlement were significantly reduced by the coatings. The residual tensile elongation of coated specimens was 2.5 times that of uncoated specimens. Comparison depth-profiling with X-ray diffraction verified the reduction of oxygen solid-solution in the α-phase for a selection of coated specimens.

Effect of copper-rich regions on tensile properties of VPPA weldments of 2219-T87 aluminum

Abstract: This study examines the relations between tensile properties and microstructural features of variable polarity plasma arc (VPPA) weldments of 2219-T87 aluminum. Crack initiation and weld failure of transverse tensile specimens of single and multipass weldments were studied. The specimens fractured on the rising portion of the stress-strain curve prior to necking, signifying that an increase in strength would accompany an increase in ductility. Of particular interest is a shallow, typically 0.001-0.003-in. (0.03-0.08-mm) deep, copper-rich region located in the crown and root corners of the weld. This region is a primary source of crack initiation and growth, due to its brittle nature and highly strained location. The brittle regions were removed by electropolishing and machining to determine their effect on weld tensile properties. The removal increased the ductility of the weld specimens, and in the case of single pass welds, actually increased the load carrying capacity. Local strain measurements and metallographic and chemical analyses are presented.

An experimental investigation of deformationinduced heating during tensile testing

Abstract: An experimental investigation of deformation heating during uniaxial tensile testing is presented for Armco interstitial-free steel (I. F. steel) and stainless steel type 310 (310SS). Temperature distributions were measured along the specimen length for tests conducted at various strain rates and subjected to various heat flow conditions (in stirred water, in air, and with insulation). Maximum temperature rises of 75 °C and 118 °C were recorded in the neck. I.F. steel shows a decreasing failure strain from ∼45 pct to ∼40 pct when natural temperature gradients develop. 310SS shows a decreasing failure strain from ∼60 pct to ∼42 pct when natural heating is allowed. In 310SS, the developed temperature gradient accounts for about one-third of this ductility reduction while the uniform temperature rise accounts for about two-thirds. The uniform temperature rise influences ductilityvia a temperaturedependent work-hardening rate. These results have been qualitatively compared with finite element modeling of these tensile tests using constitutive equations generated previously. This study provides the basis for understanding several modified forming processes and demonstrates that care must be taken in interpreting data from “standard” tensile tests since such tests reflect the thermal properties of the material and environment as well as mechanical behavior.

Behavior of Concrete Under Dynamic Tensile Loads

Abstract: A realistic nonlinear stress-strain model that can describe the dynamic tensile behavior of concrete is presented. The model is obtained by generalizing rate-independent nonlinear tensile stress-strain relations for concete. The static tensile behavior of concrete is modeled on the basis of the concept of microcrack planes. The inelastic phenomena such as microcracking occur predominantly on certain weak planes within the material. The orientations of these weak planes are considered to be uniformly distributed in the concrete. The model based on this concept describes well the static tensile test results of concrete. The affinity transformations are employed to model the effect of strain rate. The material parameters are characterized in terms of the strain rate magnitude. The present theory, which can model the dynamic tensile behavior of concrete, is compared with the dynamic tensile test data available in the literature. An equation is proposed to predict the increase of tensile strength due to an increase of strain rate. It is found that the effect of strain rate is more sensitive in tension than in compression. The model describes adequately the dynamic tensile behavior of concrete and allows more realistic dynamic analysis of concrete structures.