Showing papers on "Young's modulus published in 1986"

Fatigue of composites-fatigue modulus concept and life prediction

Abstract: Fatigue behavior of glass fiber reinforced epoxy composite materials has been studied analytically. A new concept called "fatigue modulus," which is defined as a slope of applied stress and resultant strain at a specific cycle is introduced. Fatigue modulus degradation is studied using an assumption that the fatigue modulus degrada tion rate follows a power function of fatigue cycle. Theoretical equation for predicting fatigue life is formulated using the fatigue modulus and its degradation rate. This rela tion is simplified by strain failure criterion for the practical application. It is proved that the final formula predicts the fatigue life of a glass fiber epoxy composite material better than S-N curve or Basquin's relation. An attempt is made to find the relation ship between fatigue modulus and elastic modulus by the geometric relation from stress-strain curve under the cyclic loading.

Fiber reinforced glasses and glass-ceramics for high performance applications

Abstract: The development of fiber reinforced glass and glass-ceramic matrix composites is described The general concepts involved in composite fabrication and resultant composite properties are given for a broad range of fiber and matrix combinations It is shown that composite materials can be tailored to achieve high levels of toughness, strength, and elastic stiffness, as well as wear resistance and dimensional stability

Complex composite article having improved impact resistance

Abstract: The present invention provides an improved, complex composite article of manufacture which comprises a network of high strength fibers having a tensile modulus of at least about 160 grams/denier and a tenacity of at least about 7 g/denier. An elastomeric matrix material substantially coats each of the individual fibers, and has a tensile modulus of less than about 6,000 psi, measured at 25° C. The fibers in the matrix are provided with at least one additional rigid layer on a major surface of the fibers in the matrix to produce a rigid complex composite. Composites of this construction have improved resistance to environmental hazards, improved impact resistance, and are unexpectedly effective as ballistic resistant articles such as armor or helmets.

A theoretical and numerical approach to the plastic behaviour of steels during phase transformations—II. Study of classical plasticity for ideal-plastic phases

Abstract: The response of phase-transforming steels to variations of the applied stress (i.e. the ∑-term of the classical plastic strain rate Ė cp defined in Part I) is studied both theoretically and numerically for ideal-plastic individual phases. It is found theoretically that though the stress-strain curve contains no elastic portion, it is nevertheless initially tangent to the elastic line with slope equal to Young's modulus. Moreover an explicit formula for the beginning of the curve is derived for medium or high proportions of the harder phase, and a simple upper bound is given for the ultimate stress (maximum Von Mises stress). The finite element simulation confirms and completes these results, especially concerning the ultimate stress whose discrepancy with the theoretical upper bound is found to be maximum for low proportions of the harder phase. Based on these results, a complete model is proposed for the ∑-term of the classical plastic strain rate Ė cp in the case of ideal-plastic phases.

Shear characterization of unidirectional composites with the off-axis tension test

Abstract: The influence of end constraints on accurate determination of the intralaminar shear modulus G(12) from an off-axis tension test is examined both analytically and experimentally. The Pagano-Halpin (1968) model is employed to illustrate that, when the effect of end constraints is properly considered, the exact expression for G(12) is obtained. When the effect of end constraints is neglected, expressions for the apparent shear modulus G(12)-asterisk and apparent Young's modulus Exx-asterisk are obtained. Numerical comparison for various off-axis configurations and aspect ratios is carried out using typical material properties for graphite/polyimide unidirectional composites. It is demonstrated that the end-constraint effect influences accurate determination of G(12) more adversely than it affects the laminate Young's modulus E(xx) in the low off-axis range. Experimental results obtained from off-axis tests on unidirectional graphite/polyimide specimens confirm the above. Based on the presented analytical and experimental evidence, the 45-deg off-axis coupon is proposed for the determination of the intralaminar shear modulus G(12).

Very low creep, ultra high moduls, low shrink, high tenacity polyolefin fiber having good strength retention at high temperatures and method to produce such fiber

Abstract: By poststretching, at a temperature between about 135° and 160° C., a polyethylene fiber, which has already been oriented by drawing at a temperature within 5° C. of its melting point, an ultra high modulus, very low creep, low shrink, high tenacity polyolefin fiber having good strength retention at high temperatures is obtained. The poststretching can be in multiple stages and/or with previous annealing. The poststretching should be done at a draw rate of less than 1 second -1 . Tensile modulus values over 2,000 g/d for multifilament yarn are consistently obtained for ultrahigh molecular weight-polyethylene, with tensile strength values above 30 g/d while at the same time dramatically improving creep (at 160° F. (71.1° C.) and 39,150 psi load) by values at least 25% lower than fiber which has not been poststretched. Shrinkage is improved to values less than 2.5% of the original length when heated from room temperature to 135° C. Performance at higher temperature is improved by about 15° to 25° C.

Development and Testing of Bamboo-Fibres Reinforced Plastic Composites

Abstract: Many researchers in the past have developed composites with natural fibres such as of sisal, henequen, jute and palm; but the work on the bamboo-fibre reinforced com posites is not available in the literature published so far.In the present work, an effort has been made to develop bamboo-fibre reinforced plastic (BFRP) composites using a simple casting technique. These composites have been tested for tensile strength, impact strength and Young's modulus of elasticity. It has been observed that these composites possess high strength and ductility and are useful for many structural applications. The ultimate tensile strength of some BFRP composites is more or less equal to the ultimate tensile strength of mild steel, while their density is approximately one eighth of the density of mild steel. The mechanical behaviour of these composites is similar to other commonly used composites such as Glass fibre reinforced plastics.

Creep of chemically vapour deposited SiC fibres

Abstract: The creep, thermal expansion, and elastic modulus properties for chemically vapour deposited SiC fibres were measured between 1000 and 1500°C. Creep strain was observed to increase logarithmically with time, monotonically with temperature, and linearly with tensile stress up to 800 MPa. The controlling activation energy was 480 ± 20 kJ mol−1. Thermal pretreatments near 1200 and 145O° C were found to significantly reduce fibre creep. These results coupled with creep recovery observations indicate that below 1400°C fibre creep is anelastic with negligible plastic component. This allowed a simple predictive method to be developed for describing fibre total deformation as a function of time, temperature, and stress. Mechanistic analysis of the property data suggests that fibre creep is the result of β-SiC grain boundary sliding, controlled by a small percentage of free silicon in the grain boundaries.

Frequency and temperature dependence of elastic moduli of polymers

Abstract: The frequency and temperature dependence of the elastic moduli of a number of commercially available polymers has been studied in the temperature range of 0–35 °C and for frequencies 102–106 Hz. Away from transitions a significant new relationship has been obtained, i.e., the Young’s modulus of these polymers is proportional to log of frequency. Using this relationship, together with the low and high frequency data, transitions in some of the polymers were identified.

Elastic modulus of polyethylene in the crystal chain direction as measured by X-ray diffraction

Abstract: Mesure du module de reseau cristallin dans la direction de l'axe moleculaire, de films avec differents taux d'etirage (50, 100, 200 et 300)

Ballistic-resistant fine weave fabric article

Abstract: The present invention provides an improved article of manufacture which comprises at least one network of high strength, extended chain fiber or yarn selected from the group consisting of extended chain polyethylene (ECPE) extended chain polypropylene (ECPP) fibers, extended chain polyvinyl alcohol (PVA) fiber and extended chain polyacrylonitrile (PAN) fiber The fibers and yarn have a denier of not more than about 500 and a tensile modulus of at least about 200 g/denier The fibers and yarn preferably have a tensile modulus of at least about 500 grams/denier and an energy-to-break of at least about 22 Joules/gram Optionally, a low modulus elastomeric material, which has a tensile modulus of less than about 6,000 psi, measured at about 23° C, substantially coats the fiber and yarn of the network

Polyacrylated oligomers in ultraviolet curable optical fiber coatings

Abstract: @ An ultraviolet curing liquid coating composition is disclosed which, when cured with ultraviolet light in the presence of an appropriate photoinitiator, provides buffer coatings for optical glass fiber having adequate strength at room or expected elevated temperature and stability at such elevated temperature, a high index of refraction above 1.48, and a low tensile modulus which remains low to resist microbending difficulties down to around -60°C. This coating composition consists essentially of a linear polyacrylate-terminated polyurethane or polyurea oligomer having a room temperature tensile modulus of at least 100 psi., and a tensile modulus at -60°C. which is less than 175,000 psi., when capped with 2-hydroxyethyl acrylate and cured with ultraviolet light, in admixture with a liquid acrylate-functional material which does not increase the low temperature hardness and which provides the liquidity needed for coating application. The oligomer is instead capped with a monohydric polyacrylate to provide improved cure speed without eliminating resistance to low temperature microbending.

Development of the axial Young's modulus with draw ratio of flexible-chain polymers

Abstract: Modele moleculaire d'etirage en traction; module de traction axiale; taux d'etirage maximum

The deformation of hybrid-particulate composites

Abstract: The deformation behaviour of a hybrid-particulate epoxy composite has been examined. The Young's modulusE and yield stress σγ have been determined as a function of temperature and volume fraction of rigid glass spheres, for both a simple epoxy matrix and a two-phase epoxy toughened by the presence of rubber particles. In addition, the effect of improving the particle-matrix interface with a silane bonding agent has been studied. It is found that there is a steady increase in Young's modulus with the volume fraction of spheres for all systems. In contrast, the yield stress is only found to increase with the volume fraction of rigid particles when the epoxy matrix is not toughened with rubber. It is found that the yield stress is virtually independent of particle volume fraction when a rubber-modified epoxy matrix is employed. Finally, it is found that for all compositions tested the Young's modulus and yield stress increase with increasing temperature. The overall behaviour has been discussed in terms of existing theories concerning the deformation behaviour of amorphous polymers.

Preparation and properties of zirconia-toughened mullite ceramics

Abstract: Compacts formed from high-purity fused submicrometer mullite powders, both pure and with the additions of 5 to 25 vol% ZrO2 of particle size 1, 2, or 4 μm (average), were sintered in air at 1610°C for 6 h to form dense ceramic bodies. Mechanical properties (flexural strength, Kic, and Young's modulus) were measured both before and after thermal shock. The strength after thermal shock increased considerably in systems containing additions of 10 to 20 vol% ZrO2; Kic also increased, but not so markedly. The low fraction of tetragonal ZrO2 (0.1 to 0.2) in the as-fired samples and the increase in Young's modulus after thermal shock for some strengthened samples supported the view that the interaction of residual internal stresses induced by quenching and the accompanying martensitic transformation of ZrO2 result in potential nucleation sites for microcracking. Thus, microcracking may be the predominant energy-absorbing mechanism responsible for strengthening and toughening the quenched ceramic bodies.

Ultradrawing of isotactic polypropylene films produced by gelation/crystallization from solutions.

Abstract: Films of ultra-high molecular weight isotactic polypropylene (4.4×106) were produced by gelation/crystallization from dilute solutions according to the method of Smith and Lemstra. The dried gel films could be readily stretched to a maximum draw ratio of 100 in a hot oven at 165—17 °C. For a draw ratio of 100, tensile strength and the Young’s modulus attained the maximum values of 1.56 and 40.4 GPa, respectively, at 20°C. These values are among the highest reported for polypropylene. The tensile strength was beyond the theoretical value reported by Samuels and the Young’s modulus is close to the theoretical value measured by X-ray diffraction.

Strength and elastic modulus of a porous brittle solid: an acousto-ultrasonic study

Abstract: The strength and elastic modulus of a porous brittle solid such as gypsum have been studied using an acousto-ultrasonic technique. Acousto-ultrasonics has been found to be a sensitive indicator of strength and porosity which are linearly related to some powers of a stress wave factor. New equations for porosity dependence of ultrasonic velocity, elastic modulus and strength of brittle solids have been proposed.