Showing papers on "Tensile testing published in 2002"

Analysis of the flax fibres tensile behaviour and analysis of the tensile stiffness increase

Abstract: The knowledge of the behaviour of flax fibres is of crucial importance for their use as a reinforcement for composites materials. Flax fibres were tested under tensile loading and in repeated loading–unloading experiments. We have shown that fibre stiffness increases with the strain. This phenomenon is attributed to the orientation of the fibrils with the axis of the fibre when a strain occurs. By using micro-mechanical equations, the Young's modulus of a flax fibre is estimated by taking into account the composition of the fibre and the evolution of the orientation of the fibrils during a tensile test. A good agreement is found between experimental and calculated results. The origin of the large spread observed in the mechanical characteristics is analysed here.

Composite Materials: Design and Applications

Abstract: PART ONE PRINCIPLES OF CONSTRUCTION COMPOSITE MATERIALS, INTEREST AND PROPERTIES What is Composite Material Fibers and Matrix What can be Made Using Composite Materials? Typical Examples of Interest on the Use of Composite Materials Examples on Replacing Conventional Solutions with Composites Principal Physical Properties FABRICATION PROCESSES Molding Processes Other Forming Processes Practical Hints in the Manufacturing Processes PLY PROPERTIES Isotropy and Anisotropy Characteristics of the Reinforcement-Matrix Mixture Unidirectional Ply Woven Fabrics Mats and Reinforced Matrices Multidimensional Fabrics Metal Matrix Composites Tests SANDWICH STRUCTURES: What is a Sandwich Structure? Simplified Flexure A Few Special Aspects Fabrication and Design Problems Nondestructive Quality Control CONCEPTION AND DESIGN Design of a Composite Piece The Laminate Failure of Laminates Sizing of Laminates JOINING AND ASSEMBLY Riveting and Bolting Bonding Inserts COMPOSITE MATERIALS AND AEROSPACE CONSTRUCTION Aircraft Helicopters Propeller Blades for Airplanes Turbine Blades in Composites Space Applications COMPOSITE MATERIALS FOR OTHER APPLICATIONS: Composite Materials and the Manufacturing of Automobiles Composites in Naval Construction Sports and Recreation Other Applications PART TWO: MECHANICAL BEHAVIOR OF LAMINATED MATERIALS ANISOTROPIC ELASTIC MEDIA: Review of Notations Orthotropic Materials Transversely Isotropic Materials ELASTIC CONSTANTS OF UNIDIRECTIONAL COMPOSITES: Longitudinal Modulus Poisson Coefficient Transverse Modulus Shear Modulus Thermoelastic Properties ELASTIC CONSTANTS OF A PLY ALONG AN ARBITRARY DIRECTION: Compliance Coefficients Stiffness Coefficients Case of Thermomechanical Loading MECHANICAL BEHAVIOR OF THIN LAMINATED PLATES: Laminate with Miplane Symmetry Laminate without Miplane Symmetry PART THREE: JUSTIFICATIONS, COMPOSITE BEAMS, THICK PLATES ELASTIC COEFFICIENTS Elastic Coefficients in an Orthotropic Material Elastic Coefficients for a Transversely Isotropic Material Case of a Ply THE HILL-TSAI FRACTURE CRITERION: Isotropic Material: Von Mises Criterion Orthotropic Material: Hill-Tsai Criterion Evaluation of the Resistance of a Unidirectional Ply with Respect to the Direction of Loading COMPOSITE BEAMS IN FLEXURE: Flexure of Symmetric Beams with Isotropic Phases The Case of any Cross Section (Asymmetric) COMPOSITE BEAMS IN TORSION: Uniform Torsion Location of the Torsion Center FLEXURE OF THICK COMPOSITE PLATES: Preliminary Remarks Displacement Field Strains Constitutive Relations Equilibrium Equations Technical Formulation for Bending Examples PART FOUR: APPLICATIONS LEVEL 1 Simply Supported Sandwich Beam Poisson Coefficient of a Unidirectional Layer Helicopter Blade Transmission Shaft for Trucks Flywheel in Carbon/Epoxy Wing Tip Made of Carbon/Epoxy Carbon Fibers Coated with Nickel Tube Made of Glass/Epoxy Under Pressure Filament Wound Reservoir, Winding Angle Filament Wound Reservoir, Taking into Account the Heads Determination of the Volume Fraction of Fibers by Pyrolysis Lever Arm Made of Carbon/Peek Unidirectionals and Short Fibers Telegraphic Mast in Glass/Resin Unidirectional Ply of HR Carbon Manipulator Arm of Space Shuttle LEVEL 2 Sandwich Beam: Simplified Calculations of the Shear Coefficient Procedure for Calculation of a Laminate Kevlar/Epoxy Laminates: Evolution of Stiffness Depending on the Direction of the Load Residual Thermal Stresses Due to Curing of the Laminate Thermoelastic Behavior of a Tube Made of Filament Wound Glass/Polyester Polymeric Tube Loaded by Thermal Load and Creep First Ply Fracture of a Laminate Ultimate Fracture Optimum Laminate for Isotropic Stress State Laminate Made of Identical Layers of Balanced Fabric Wing Spar in Carbon/Epoxy Determination of the Elastic Characteristics of a Carbon/Epoxy Unidirectional Layer from Tensile Test Sail Boat Shell in Glass/Polyester Determination of the in-Plane Shear Modulus of a Balanced Fabric Ply Quasi-Isotropic Laminate Orthotropic Plate in Pure Torsion Plate made by Resin Transfer Molding (RTM) Thermoelastic Behavior of a Balanced Fabric Ply LEVEL 3 Cylindrical Bonding Double Bonded Joint Composite Beam with Two Layers Buckling of a Sandwich Beam Shear Due to Bending in a Sandwich Beam Column Made of Stretched Polymer Cylindrical Bending of a Thick Orthotropic Plate under Uniform Loading Bending of a Sandwich Plate Bending Vibration of a Sandwich Beam Appendix 1: Stresses in the Plies of a Laminate of Carbon/Epoxy Loaded in its Plane Appendix 2: Buckling of Orthotropic Structures Bibliography

Aluminum coatings via kinetic spray with relatively large powder particles

Abstract: Coatings have been produced by entraining relatively large diameter metal powders in a supersonic airflow. For the first time, most of the particles in the powders have diameters >50 μm. Substantial plastic deformation is involved in the conversion of the particle's kinetic energy into heat and strain energy in this kinetic spray process. As suggested by simple estimates and confirmed by coating grain structures, the particles are not melted or thermally softened in this coating process. These coatings have a relatively low oxide content, low thermal stress, high adhesion, low porosity and hardness somewhat higher than those of corresponding bulk materials. Threshold or critical velocities for coating formation are discussed. Critical velocities for the relatively large particles were observed to be substantially less than have been reported earlier for smaller diameter (<50 μm) particles. Coating particle rotation and deformation due to particle impact resulted in a corresponding decrease in porosity. Bond formation, particle deformation and grain deformation were found to be highly anisotropic, depending on the direction of the incident particle velocity. At higher incident velocities, increasing metallic bond formation between particles was observed. This is consistent with a metallic form for stress/strain curves obtained via tensile tests on Al coatings removed from the substrate. The coating elastic modulus was found to be less than half that of bulk Al. Measured ultimate tensile strengths and yield points of Al coatings were comparable to those of bulk Al. This may be due to work hardening resulting from the plastic deformation necessary for coating formation. These tensile test results are consistent with coating cohesive strengths as measured by stud pull tests. Higher powder feed rates produced coatings with higher failure loads in three point bending, higher coating cohesion and lower coating strength anisotropy, presumably due to a peening effect. Four velocity-dependent stages of coating formation are proposed based on observations reported here. Coating properties arise from a competition between these stages. Parallels with models of dynamic (explosive) powder compaction are made. This is the first comprehensive model for kinetic spray coating formation.

Microstructures and mechanical properties of 6061 aluminum alloy processed by accumulative roll-bonding

Abstract: Accumulative roll-bonding (ARB) process is an intense plastic deformation process that has been performed for a 6061 aluminum alloy to develop ultra-fine grains below 1 μm in diameter and to improve mechanical properties. The ARB process up to eight cycles is performed at ambient temperature under unlubricated conditions. The ultra-fine grains surrounded by clear boundaries begin to appear at the third cycle, and the specimen after eight cycles shows a microstructure covered with ultra-fine grains with an average diameter of 310 nm. The tensile strength of the ARB processed 6061 alloy increases with the number of ARB cycles (equivalent total strain), and after eight cycles it reaches the maximum of 363 MPa, which is about three times of the initial. On the other hand, the elongation drops abruptly at the first cycle, above which it decreases progressively with the number of ARB cycles. The hardness of the specimens ARBed by one, three and five cycles varies inhomogeneously in the thickness direction; having peak values near the surface and the center. This is due to the redundant shear strain and wire brushing. The results show that the ARB process is effective for grain refinement and strengthening of 6061 alloy.

In-situ tensile testing of nano-scale specimens in SEM and TEM

Abstract: We present a new experimental method for the mechanical characterization of freestanding thin films with thickness on the order of nanometers to micrometers. The method allows, for the first time, in-situ SEM and TEM observation of materials response under uniaxial tension, with measurements of both stresses and strains under a wide variety of environmental conditions such as temperature and humidity. The materials that can be tested include metals, dielectrics, and multi-layer composites that can be deposited/grown on a silicon substrate. The method involves lithography and bulk micromachining techniques to pattern the specimen of desired geometry, release the specimen from the substrate, and co-fabricate a force sensor with the specimen. Co-fabrication provides perfect alignment and gripping. The tensile testing fits an existing TEM straining stage, and a SEM stage. We demonstrate the proposed methodology by fabricating a 200 nm thick, 23.5 μm wide, and 185 μm long freestanding sputter deposited aluminum specimen. The testing was done in-situ inside an environmental SEM chamber. The stress-strain diagram of the specimen shows a linear elastic regime up to the yield stress σy MPa, with an elastic modulusE=74.6 GPa.

Mechanical properties of nickel silicon carbide nanocomposites

Abstract: Nanocomposite materials consisting of a nanocrystalline Ni matrix (grain size 10–15 nm) reinforced with sub-micron size SiC particulates (average particle size: 0.4 μm) up to 10.5 vol.% have been produced by pulse electrodeposition. Substantial improvements in mechanical properties including hardness, yield and tensile stress were obtained for the nanocomposite material, as compared with conventional Ni–SiC composites with a matrix grain size in the micrometer range. Tensile strengths up to four times that for conventional polycrystalline Ni and two times that for conventional polycrystalline Ni–SiC of comparable SiC content was measured. The tensile and yield strengths of the nanocomposite material with SiC content less than 2 vol.% were higher than those for pure nanocrystalline Ni of comparable grain size. For these nanocomposites an unexpected increase in tensile ductility was also observed when compared to pure nanocrystalline nickel. At higher SiC content (>2 vol.%) the strength and ductility were found to decrease to the detriment of the nanocomposite. Particle clustering was considered the main cause of this decrease.

Durability of Glass Fiber-Reinforced Polymer Reinforcing Bars in Concrete Environment

Abstract: Accelerated aging tests are being conducted on more than 20 types of glass fiber-reinforced polymer (GFRP) reinforcing bars, which are produced from different combinations of constituent materials, manufacturing parameters, sizes and shapes, and surface coatings. The specimens are being subjected to various sustained tensile loading (22 to 68% of ultimate strength) in three types of alkaline environments: NaOH, simulated pore-water solution, and embedded in concrete. Time to rupture or residual strength, as applicable, have been determined. Additionally, stress corrosion mechanisms were evaluated by various microstructural analyses. The results showed clearly that alkaline ions and moisture could penetrate or diffuse through the resin (or through cracks and voids) to the interphases and the fibers. For GFRP bars embedded in moist concrete under various sustained stress levels, three types of stress corrosion mechanisms have been identified: stress dominated, crack propagation dominated, and diffusion domi...

Application of MEMS force sensors for in situ mechanical characterization of nano-scale thin films in SEM and TEM

Abstract: We present a novel tensile testing technique utilizing MEMS force sensors for in situ mechanical characterization of sub-micron scale freestanding thin films in SEM and TEM. Microfabrication techniques are used to cofabricate the thin film specimens with force sensors to produce the following unique features: (1) small setup size to fit in SEM and TEM for in situ experiments, (2) ability to measure tensile pre-stress in specimen, (3) alignment between specimen and applied loading axes with lithographic precision, (4) no extra gripping mechanism required, and (5) ability to measure creep strain in the material. The technique allows single or multilayers of materials that can be deposited/grown on silicon substrate to be tested. We demonstrate the technique by testing a 100 nm thick, 8.8 μm wide and 275 μm long freestanding aluminum specimen (average grain size about 50 nm) in situ inside an environmental SEM chamber, and present another setup for similar experiment in TEM. Experimental results strongly suggest that at this size scale: (1) elastic modulus does not change, (2) size effects on yield strength are pronounced (63 times the bulk pure aluminum yield stress), and (3) permanent strain hardening effects are absent.

Mechanical Properties of Hardened AISI 52100 Steel in Hard Machining Processes

Abstract: This paper provides an approach using tensile tests at elevated temperatures to estimate mechanical properties of the work material for both elastic and plastic deformations in a broad range of strain, strain rate, and temperature in machining. The proposed method has been applied to estimate mechanical properties of hardened AISI 52100 steel in hard machining. Tensile testing is shown capable of estimating the mechanical properties of both elastic and plastic regions with large strains at elevated temperatures. Flow stresses at high strain rates in machining can be obtained by extrapolating the data from tensile tests by using the velocity-modified temperature. Flow stress data from tensile and cutting tests is consistent with regard to the velocity-modified temperature. Temperature is the dominant factor of mechanical properties of this material, while the effect of strain rate is secondary. Cutting forces and chip geometry predicted by the 3D FEM simulation of hard turning using the material property data obtained from the developed method agree well with the experimental data. @DOI: 10.1115/1.1413775#

On the characteristics of Portevin-Le Chatelier bands in aluminum alloy 5182 under stress-controlled and strain-controlled tensile testing

Abstract: Plastic instabilities associated with the Portevin–Le Chatelier (PLC) effect are investigated in an Al-based alloy of the 5000 series, in a wide range of temperatures and loading rates. The domains of occurrence of the PLC effect are explored and compared for constant stress rate and constant strain rate tensile testing. In both cases, experimental results show that the PLC domains are bounded towards high temperatures and loading rates. The critical strain for the onset of repeated yielding increases with increasing loading rate at low temperatures and high loading rates (normal behaviour), while it decreases at high temperatures and low loading rates (inverse behaviour), with different types of serration associated with the normal and the inverse behaviour. A simple model is proposed to explain this relation between the PLC type and the behaviour of the critical strain. Moreover, the specimen surface finish is found to have a significant influence on the stress–strain curves and the band propagation velocities. Finally, the experimentally observed PLC domain is shown to be in good agreement with a physical model of the dynamic strain ageing associated with the PLC effect.

Effects of humidity on Young's modulus in poly(methyl methacrylate)

Abstract: Tensile tests on poly (methyl methacrylate) (PMMA) were conducted to clarify the effects of humidity and strain rate on tensile properties, particularly Young's modulus. Prior to the tensile tests, specimens were kept under various humidity conditions at 293 K, which were the same as the test conditions, for a few months to adjust the sorbed water content in the specimens. The tensile tests were performed under each humidity condition at three different strain rates (approximately 1.4 × 10−3, 1.4 × 10−4, and 1.4 × 10−5 s−1). Stress-strain curves changed with humidity and strain rate. Young's moduli were also measured at small applied stresses (below 6.7 MPa) under various humidity conditions at 293 K. Young's modulus decreases linearly with increasing humidity and a decreasing logarithm of strain rate. These results suggest that Young's modulus of PMMA can be expressed as a function of two independent parameters that are humidity and strain rate. A constitutive equation for Young's modulus of PMMA was proposed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 460–465, 2002; DOI 10.1002/polb.10107

Modeling dendritic structure and mechanical properties of Zn–Al alloys as a function of solidification conditions

Abstract: In the present article, some important trends have been shown regarding the relationship between mechanical properties, microstructure and solidification variables of Zn–Al alloys castings. Some theoretical dendritic growth models, expressing secondary spacings as function of tip growth rate or local solidification time, have been tested against experimental data obtained during unsteady-state solidification. Based on these dendritic models, on analytical expressions describing the position of solidus and liquidus isotherms in the unidirectional solidification of binary alloys and on experimental results concerning tensile testing of casting samples, expressions have been developed permitting a correlation between ultimate and yield strength, dendrite secondary spacings and solidification processing variables.

Permeability of cracked steel fiber-reinforced concrete

Abstract: This research explores the relationship between permeability and crack width in cracked, steel fiber-reinforced concrete. In addition, it inspects the influence of steel fiber reinforcement on concrete permeability. The feedback-controlled splitting tension test (also known as the Brazilian test) is used to induce cracks of up to 500 μm (0.02 in.) in concrete specimens without reinforcement, and with steel fiber reinforcement volumes of both 0.5 and 1%. The cracks relax after induced cracking. The steel fibers decrease the permeability of specimens with relaxed cracks larger than 100 μm.

Influence of intermetallic compounds on the adhesive strength of solder joints

Abstract: This study investigates the influence of intermetallic compound (IMC) growth on the adhesive strength of solder joints. 100Sn and 60Sn40Pb solders were used to solder electrolytic copper wires end to end. Soldered samples were then subjected to high temperature storage testing. The resulting interfacial IMCs in both solders were composed of Cu6Sn5 and Cu3Sn. IMC in the 100Sn solder joint grew faster than in the 60Sn40Pb. The growth behavior of Cu6Sn5 and Cu3Sn were subject to lead concentration. Results of tensile testing revealed an adhesive strength for 60Sn40Pb of 77.3 MPa, higher than the 50.0 MPa for 100Sn. 60Sn40Pb was found more sensitive to high temperature storage than 100Sn.

Coupled damage and plasticity modelling in transient dynamic analysis of concrete

Abstract: In a concrete structure subjected to an explosion, for example a concrete slab, the material is subjected to various states of stress which lead to many modes of rupture. Closer to the explosive, a state of strong hydrostatic compression is observed. This state of stress produces an irreversible compaction of the material. Away from the zone of explosion, confinement decreases and the material undergoes compression with a state of stress, which is slightly triaxial. Finally, the compression wave can be reflected on a free surface and becomes a tensile wave, which by interaction with the compression wave, produces scabbing. We present, in this paper, a model aimed at describing these three failure modes. It is based on visco-plasticity and rate dependent damage in which a homogenization method is used in order to include the variation of the material porosity due to compaction. The model predictions are compared with several experiments performed on the same concrete. Computations of split Hopkinson tests on confined concrete, a tensile test with scabbing, and an explosion on a concrete slab are presented.