Showing papers on "Ultimate tensile strength published in 1987"

A Progressive Damage Model for Laminated Composites Containing Stress Concentrations

Abstract: A progressive damage model is presented for notched laminated composites subjected to tensile loading. The model is capable of assessing damage in laminates with arbitrary ply-orientations and of predicting the ultimate tensile strength of the notched laminates. The model consists of two parts, namely, the stress analysis and the failure analysis. Stresses and strains in laminates were analyzed on the basis of classical lamination theory with the consideration of material nonlinearity. Damage accumulation in laminates was evaluated by proposed failure criteria combined with a proposed property degradation model. A nonlinear finite element program, based on the model, was developed for lami nates containing a circular hole. Numerical results were compared with the experimental data on laminates containing an open circular hole. An excellent agreement was found be tween the analytical prediction and the experimental data.

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

Influence of structural and morphological factors on the mechanical properties of the polyethylenes

Abstract: Relations force-longueur a temperature ambiante determinees pour une serie de polyethylenes d'une large gamme de masse moleculaire et contribution moleculaire

Mechanical properties of particulate filled polymers

Abstract: The mechanical properties of several types of inorganic fillers were investigated in a number of different thermoplastic polymers. The fillers included minerals, such as talc and silicon carbide, and metals, such as aluminum flake and stainless steel fibers. The polymers included General Electric's Noryl, acrylonitrile-butadiene-styrene terpolymer, polypropylene, and modified polypropylene. The talc and some of the aluminum flake were treated with coupling agents to improve interfacial adhesion to the polymers. The results showed that the modulus of the filled polymers was a function only of the concentration of filler used up to 40 volume percent filler. The tensile strength of the filled compositions depended very strongly on the degree of interfacial bond developed between the polymer and the filler. The interfacial bond strength depended on the effectiveness of the coupling agents and the inherent wetting ability of the polymer. Of the polymers investigated in this study, Noryl showed the greatest degree of inherent wetting to inorganic fillers. Chemical modification of polypropylene also resulted in greater adhesion to fillers. The impact strength of filled compounds had an even more complex response, because, in addition to the concentration of the filler, and strength of the polymerfiller interface, it depends on the mechanism of crack propagation.

The Effects of Crystallinity on the Mechanical Properties of PEEK Polymer and Graphite Fiber Reinforced PEEK

Abstract: The mechanical properties of PEEK 150P polymer and APC-2 graphite/PEEK com posite were measured at different crystallinities, from 0 to 40 weight percent. For PEEK 150P the tensile, compressive, an...

Self‐Reinforced melt processible polymer composites: Extrusion, compression, and injection molding

Abstract: Rheological properties, extrusion, fiber spinning, compression, and injection molding of blends of polycarbonate and two thermotropic liquid crystal polymers based on wholly aromatic copolyesters have been studied. Blends were prepared using an internal Banbury mixer and static Koch mixer. Based upon differential scanning calorimetry and dynamic mechanical measurements, these blends have been shown to be incompatible in the entire range of concentrations. During extrusion and injection molding at high strain rates, it has been observed that thermotropic liquid crystal polymer at concentrations 2.5, 5, and 10 percent by weight in situ forms high modulus and high strength fibers within the polycarbonate matrix leading to self-reinforced polymer composites. The tensile strength of the composite containing 10 percent of liquid crystal polymer exceeds that of the pure components. In addition, anisotropy of properties of the injection molded parts has been found to substantially reduce in a comparison with that of liquid crystal polymer. The processing conditions and technique for the production of self-reinforced polymer composite during processing of the blends have been identified. This has been done by measurements of mechanical properties, direct observation of morphology, and by theoretical calculation using simplified composite theory for the unidirectional continuous fiber-reinforced composites. At the high concentrations, 25 and 50 percent by weight, thermotropic liquid crystal polymer forms large spherical droplets inside polycarbonate leading to highly brittle material. This is in distinction from the fibrous, high modulus tough composites formed at the lower concentrations.

Tensile recoil measurement of compressive strength for polymeric high performance fibres

Abstract: Recoil forces acting on the broken ends of a fibre after tensile failure are known to cause substantial damage to polymeric high performance fibres. This damage is the result of compressive stresses developed during snap-back, or recoil, whose magnitude exceeds the compressive strength of the fibre. An analysis describing the axial stress history experienced by a fibre following a tensile failure has been performed and the results have led to the development of a simple, single filament, recoil technique for measuring fibre compressive strength. A number of polymeric high performance fibres were examined using the technique and compressive strengths measured are in excellent agreement with values obtained from composite tests.

Correlation of tensile properties, deformation modes, and phase stability in commercial β-phase titanium alloys

Abstract: The effect of plastic deformation mode on tensile properties of quenched commercial β-phase titanium alloys has been investigated at approximately constant grain size and oxygen content. In addition, stability of β-phase has been estimated from ω-reflections or diffuse streaking in electron diffraction patterns in a manner similar to the previous works on binary β-phase titanium alloys. Dominant mode of plastic deformation is {332} twinning in the alloys with large instability of β-phase, such as Ti-11.5Mo-6Zr-4. 5Sn and Ti-15Mo-5Zr, and is crystallographic slip in the alloys with small instability of β-phase, such as Ti-15Mo-5Zr-3Al, Ti-3Al-8V-6Cr-4Mo-4Zr, Ti-15V-3Cr-3Al-3Sn, Ti-8Mo-8V-2Fe-3Al, and Ti-13V-11C-3Al. Twinning leads to low yield strength and large elongation, while slip results in high yield strength and small elongation in agreement with binary and termary β-phase titanium alloys.

Strengthening of Oxide Ceramics by Transformation‐Induced Stress

Abstract: Alumina-zirconia composites were fabricated by isostatic pressing and sintering of powder mixtures in such a way that bar-shaped specimens consisted of three layers. The outer layers contained A12O3 and unstabilized ZrO2 while the central layer contained A12O3 and partially stabilized ZrO2 (with 2 mol% Y2O3). When cooled from the sintering temperature, some of the zirconia in the outer layers transformed to the monoclinic form while zirconia in the central layer was retained in the tetragonal form. The transformation of zirconia in the outer layers led to the establishment of surface compressive stresses and balancing tensile stresses in the bulk. The existence of surface compressive stresses was verified by a strain gauge technique and bending strength measurements on samples with varying thickness of the outer layers. The layered composites exhibited greater strength in comparison with monolithic Al2O3-ZrO2 specimens. Further, variation of strength in bending with outer layer thickness (for a fixed total thickness) indicated that failure occurred from internal flaws. Scanning electron microscopy of fracture surfaces revealed that strength-limiting flaws were voids located in the central layer near the interface separating the central and the outer layers.

Skin-Core morphology and failure of injection-molded specimens of impact-modified polypropylene blends

Abstract: The structure-property relationship as well as the failure phenomena of injection molded polypropylene (PP) blends modified with ethylene/propylene/diene terpolymer (EPDM) and thermoplastic polyolefinic rubber (TPO) were investigated. Single and double-gated tensile bars were injection molded by different Injection speeds. Microscopic studies on the failure behavior of knit lines were carried out using microtomed sections taken from the doublegated specimens. It was found that during injection molding, a skin-core morphology is formed in both the continuous PP matrix as well as in the modified PP blends containing rubber particles of various deformation. The characteristics of the latter are in agreement with those described by the Tadmor flow model. The skin consists of a thin pure PP layer, whereas the subsurface layer contains more or less elongated rubbery particles due to the elongational flow at the wall. The deformation of the rubbery particles decreases, but their concentration increases with increasing distance from the skin towards the core. The deformed particles are oriented tengentionally to the flow front profile. Failure during tensile and tensile impact loading is initiated in the shear zone along the skin-core boundary. This zone has a transcrystalline character and favors the formation of crazing. Final fracture of the bars depends, however, on how crazing and shear yielding simultaneously interact. Their interaction is a function of the average particle size of the dispersed phase. Above an average particle size of 0.6 μm, crazing is prevented by shear bands. For injection molding of PP/rubber blends a moderate injection speed is recommended, if the melt viscosities of the components are closely matched. In this way a pronounced dispersion gradient of the rubber particles across the plaque thickness is avoided. However, for the blends modified with rubber of high viscosity ratio and greater melt elasticity, use of higher injection speed is advantageous. Here, the higher shear stress field decreases the average particle size taken into the direction perpen dicular to the lead, since the cross section of the stronger deformed particle decreases.

Vacuum mixing of acrylic bone cement

Abstract: A partial-vacuum (500–550 mmHg), slow-speed (2 Hz) system for optimal blending of the liquid and powder components of Simplex-P acrylic bone cement was developed to eliminate five different sources of porosity observed with x-ray during the course of cement preparation and specimen fabrication. The vacuum mixing system produces set speciments of less than 1% porosity that have significant improvements over specimens prepared with conventional mixing in the mechanical properties of tensile and compressive strength and uniaxial tensile fatigue life. Hence, a much stronger cement can be available in surgery without any change in original chemical composition.

Yielding and deformation behavior of the single crystal superalloy PWA 1480

Abstract: Interrupted tensile tests were conducted to fixed plastic strain levels in 100 ordered single crystals of the nickel based superalloy PWA 1480. Testing was done in the range of 20 to 1093 C, at strain rate of 0.5 and 50 percent/min. The yield strength was constant from 20 to 760 C, above which the strength dropped rapidly and became a strong function of strain rate. The high temperature data were represented very well by an Arrhenius type equation, which resulted in three distinct temperature regimes. The deformation substructures were grouped in the same three regimes, indicating that there was a fundamental relationship between the deformation mechanisms and activation energies. Models of the yielding process were considered, and it was found that no currently available model was fully applicable to this alloy. It was also demonstrated that the initial deformation mechanism (during yielding) was frequently different from that which would be inferred by examining specimens which were tested to failure.

Drawing of virgin ultrahigh molecular weight polyethylene: an alternative route to high strength/high modulus materials. Part 2: Influence of polymerization temperature.

Abstract: The synthesis of ultra-high molecular weight polyethylene films and the production of high strength/high modulus tapes and filaments drawn directly from the virgin polymer are described. The study particularly focuses on the effect of the polymerization temperature on the deformation behaviour of the virgin UHMW polyethylene films. These results are discussed within the framework of the entanglement concepts for deformation of weakly bonded macromolecules. The developrnent of the room temperature Young's modulus and the tensile strength with draw ratio is presented and compared with modulus and tenacity/draw ratio relations observed for melt and solution crystallized polyethylene.

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 effect of matrix properties on reinforcement in short alumina fibre-aluminium metal matrix composites

Abstract: The effect of the alloy matrix on room-temperature strengthening in δ-alumina-reinforced aluminium alloys has been investigated. Alloy matrices fell into two families exhibiting significantly different fibre-strengthening response. The first gave rise to little or no improvement in the room-temperature strength, while the second gave significant improvements by up to 300%. It is shown that a simple Rule of Mixtures (ROM) strength analysis, modified to account for the discontinuous and random orientation of the reinforcement, can adequately explain these responses. Little or no reinforcement occurs when the matrix properties result in a high value for the critical volume fraction VCRIT which must be exceeded to produce any increase in strength. However, by careful selection of the matrix alloyV CRIT can be reduced, thus giving significant reinforcement of the room-temperature strength. This analysis shows that for optimum room-temperature reinforcement the matrix alloys should exhibit a low rate of work-hardening. In certain alloys reinforcement levels were in excess of those predicted by the ROM analysis. It is proposed that this occurs in relatively low-strength matrices as a result of dispersion strengthening of the matrix due to the presence of the fibre array.

High-strength ceramics through colloidal control to remove defects

Abstract: Although the theoretical tensile strength of alumina is ∼46 GPa (ref 1), conventional powder processing rarely gives products better than 05 GPa because large defects, ∼50–100 µm in size, are invariably trapped during powder compaction2,3 Thin-film, fibrous, melt-processed and vapour-deposited ceramics can achieve higher strengths of several GPa (refs 4–6), but such processes are much more expensive than simple sintering of powder compacts Here we show how colloidal control of powders to remove agglomerates can be used to give high-strength sintered ceramics: for example, a commercial alumina powder can be improved from 037 to 104 GPa in bend strength

Mechanical properties of vapour-grown carbon fibres

Abstract: Vapour-grown carbon fibres are formed by depositing layers of carbon from hydrocarbon pyrolysis on precursors of filamentous carbon. They are partially graphitic with the basal planes preferentially oriented as nested coaxial cylinders. As the fibres are axially strained, their stiffness increases by about 28%, probably due to strain-induced increase in the preferred orientation. Vapour-grown fibres 7.5 mu m in diameter have a tensile strength of 2.92 GPa (0.42*106 PSI) and a modulus of 237 GPa (34*106 PSI). Both the tensile strength and the modulus shows an apparent dependence on fibre diameter. Larger-diameter fibres have a lower modulus and tensile strength than smaller-diameter fibres. This apparent dependence of fibre mechanical properties on diameter is shown to be due to nonuniform carbon deposition rates along the length of the fibre growth reactor. In a given growth experiment, a range of fibre diameters are produced in a fixed period with the larger-diameter fibres deposited at a higher rate. X-ray studies of fibres having a range of diameters and hence deposition rates show that the graphitic ordering of small-diameter fibres (low deposition rates) is more complete than that of large-diameter fibres, thus accounting for the larger modulus of small-diameter fibres.

In vitro chemical degradation of poly(glycolic acid) pellets and fibers

Abstract: The influence of macroscopic dimensions, heat treatment, and polymer morphology on the chemical degradation of poly(glycolic acid) (PGA) fibers and pellets was examined in media of different pH values by monitoring the sample mass, dimensions, crystallinity, mechanical strength, and surface character. The degradation was found to be chemically controlled and independent of fiber size. The rate was an order of magnitude faster in alkaline vs. acidic media. In general, the pellets degraded faster than fibers, and while the latter showed little surface deterioration, scanning electron photomicrographs of the pellets revealed considerable surface degradation with circumferential microcracks progressing into longitudinal cracks with increasing immersion times and pH. Concomitantly, DSC measurements showed a steady increase in crystallinity for both fibers and pellets. The fiber tensile strength decline was independent of diameter and more drastic in alkaline media. Additionally, the heat-treated fiber was always stronger than the non-heat-treated one. It is concluded that crystallinity and polymer chain orientation, in addition to immersion media, influence PGA degradation. Also, the loss in strength results from chain scission in the amorphous regions while mass loss occurs when polymer chains become small enough to be soluble. These different variables offer a means of modifying PGA fiber tensile properties.

Effect of thermal history on mechanical properties of polyetheretherketone below the glass transition temperature

Abstract: The effect of thermal history on the tensile properties of polyetheretherketone neat resin films was investigated at different test temperatures (125, 25, and -100) using four samples: fast-quenched amorphous (Q); quenched, then crystallized at 180 C (C180); slowly cooled (for about 16 h) from the melt (SC); and air-cooled (2-3 h) from the melt (AC). It was found that thermal history significantly affects the tensile properties of the material below the glass transition. Fast quenched amorphous films were most tough, could be drawn to greatest strain before rupture, and undergo densification during necking; at the test temperature of -100 C, these films had the best ultimate mechanical properties. At higher temperatures, the semicrystalline films AC and C180 had properties that compared favorably with the Q films. The SC films exhibited poor mechanical properties at all test temperatures.

Kinetic model for tensile deformation of polymers

Abstract: Deformation de polymeres flexibles solides. Modele base sur la theorie de vitesse d'activation chimique d'Eyring. Application au polyethylene cristallise a l'etat fondu