Showing papers on "Ultimate tensile strength published in 1978"

Influence of martensite composition and content on the properties of dual phase steels

Abstract: A study has been made of the mechanical properties of dual phase (martensite plus ferrite) structures produced when Fe-Mn-C alloys are quenched from the austenite plus ferrite phase field, so as to give a series of alloys with constant ferrite and martensite compositions but varying percent martensites. It is found that the strength of a dual phase structure is dependent on the ferrite grain size and the volume fraction of martensite, and is independent of the composition and strength of the martensite. In agreement with previous work the ductility of these steels is superior to that for standard HSLA steels at the same tensile strength. As shown in a previous paper the strength and ductility as a function of percent martensite are in agreement with Mileiko’s theory of composites of two ductile phases. This theory and the results indicate that the superior ductility of dual phase steels is largely a consequence of the high strength (fine grained), highly ductile (low interstitial content) ferrite matrix.

Anomalous increase in strength of in situ formed Cu‐Nb multifilamentary composites

Abstract: Cu‐Nb wire composites with 0.105, 0.148, and 0.182 volume fraction of Nb filaments were produced in situ and their mechanical properties measured as a function of filament size and interfilament spacing. The yield stress and the ultimate tensile strength increased with both niobium volume fraction and overall composite reduction. At room temperature, the ultimate tensile strength of the Cu–18.2 vol% Nb composite reduced by 99.999% in cross‐sectional area (100–200 A filament thickness) reached the value of 2230 MN/m2 (323 ksi) and further increased to 2850 MN/m2 (413 ksi) when measured at 77 °K. These values are higher by a factor of 4 than the values predicted by the rule of mixtures based on the highest reported strength of both niobium and copper. The composite strength is as high as that of the best copper whiskers and is shown to closely approach the theoretical strength of the material. The anomalous increase in strength despite the low volume fraction of reinforcing filaments suggests that the filam...

Development of high tensile strength silicon carbide fibre using an organosilicon polymer precursor

Abstract: THE high tensile strength SiC fibre developed in our laboratory1–5 is extremely heat-resistant and its wettability by metals is good. Metal–matrix composites reinforced with the SiC fibre should therefore be of practical use. Polycarbosilane, the precursor of the fibre, is synthesised by thermal decomposition under high pressure of poly dimethylsilane in an autoclave. To produce the SiC fibre on an industrial scale, polycarbosilane needs to be produced in large quantities with high yield. The autoclave method requires a large amount of space, so the operation is inconvenient and uneconomic. We have, therefore, developed a new method of synthesising the polycarbosilane at normal pressure by adding several wt % of polyborodiphenylsiloxane6 to polydimethylsilane. The structure and properties of the new polycarbosilane, and the SiC fibre obtained from it are described here.

Synthesis of continuous silicon carbide fibre with high tensile strength and high Young's modulus: Part 1 Synthesis of polycarbosilane as precursor

Abstract: Polycarbosilane as the precursor of continuous SiC fibre was synthesized by thermal decomposition of polydimethylsilane. The structure of the polycarbosilane is concluded to be similar to that of polysilapropylene by the measurements of i.r. spectra, NMR spectra and chemical analyses. Its formation mechanisms are initially the formation of carbosilane by thermal decomposition of polydimethylsilane and then the increase in molecular weight by dehydrogenation-condensation of the carbosilane. Molecular structure and molecular weight distribution of the polycarbosilane depend on the reaction temperature.

Finite Element Model for Masonry

Abstract: A method for the in-plane analysis of clay masonry walls is presented. The proposed finite element model reproduces the nonlinear characteristics of masonry caused by material nonlinearity and progressivee joint failure. Masonry is considered as an assemblage of elastic brick continuum elements acting in conjunction with linkage elements simulating the mortar joints. The joint elements are assumed to have high compressive strength (with nonlinear deformation characteristics), low tensile strength, and limited shear strength depending upon the bond strength and degree of compression present. The material properties for this model are determined from uniaxial tests on bricks and masonry panels. Tests on a masonry deep beam are used as a basis for comparison between predicted theory and experimental evidence.

Shear in beam - column joints in seismic design of steel frames

Abstract: This paper discusses the importance of joint shear in the response of frame structures to severe earthquakes. Presently used AISC design criteria for joint shear are reviewed in the light of limited experimental evidence. The effects of high shear in joints on the strength, stiffness, and energy-dissipation characteristics of frames are discussed. The most important conclusions can be briefly summarized: Joints usually are very ductile elements capable of undergoing severe inelastic strain reversal without a decrease in strength. The shear force defined by the AISC design equation for combined gravity and lateral loads usually causes some inelastic deformation in joints. This is reduced when the allowable shear stress is modified by the factor alpha, which accounts for the effect of the axial force in the column on the yield stress in shear. Solutions for the ulimate shear strength, associated with controlled inelastic distortions, are given, for joints with unreinforced and reinforced webs, respectively. When joints are designed according to allowable stress criteria, inelastic deformations may be concentrated primarily in the joints and to a lesser degree in plastic hinge regions of beams and columns. Maximum strength and stiffness of frames is attained when all joints are designed for the maximum shear force that can be developed based on the strength capacity of the members framing into the joint. The need for this design criterion has not been fully established, although it is widely used in areas of high seismicity. If this criterion is used, the joints should be permitted to participate in energy dissipation through inelastic deformations. Joint distortions contribute significantly to the elastic story drift in frames. Equations are given which permit an estimate of the effect of these distortions on the lateral deflections.

The deformation behavior of a vanadium-strengthened dual phase steel

Abstract: A study has been made of the mechanical properties of dual phase (martensite plus ferrite) structures produced when a V containing HSLA steel is cooled in a controlled manner from either the austenite or austenite plus ferrite phase fields Such a heat treatment results in the pearlite regions and carbide particles of the standard V steel being replaced by martensite; this leads to a decrease in the yield stress and an increase in ductility while the tensile strength is essentially unchanged The fatigue of dual phase steels is slightly superior in the high strain life (ductility controlled) region and slightly inferior in the low strain life (yield dominated) region when compared to standard V steel The replacement of the pearlite and cementite particles which can nucleate cracks, by more ductile martensite islands results in improved Charpy impact properties The strength and the ductility of the dual phase materials is shown to be in agreement with a theory of composites with two ductile phases This theory then allows one to understand the relative importance of various microstructural features in controlling strength and ductility In this way it is found that the key to the superior elongation (at a constant tensile strength) is largely due to the high strength (fine grained), highly ductile ferrite matrix

Dynamic studies of the tensile deformation and fracture of pearlite using high-resolution 200-KV sem

Abstract: Dynamic studies of the tensile deformation and fracture of pearlite using high-resolution 200-KV sem

A computer simulation of the tension test

Abstract: A dynamic finite-difference computer program is used to calculate the quasi-static necking deformation of a round tensile bar to 71 per cent reduction in area. Finite strain and rotation are accounted for. We modelled the behavior of A-533 Grade B Class 1 nuclear-pressure-vessel steel as elastic work-hardening plastic material, using J2-flow theory and a flow curve obtained from a simple tensile test. Up to the time of fracture, computed results of neck radius vs load and elongation, load vs elongation, and neck profile vs neck radius compare favorably with experimental results. We present the macroscopic stress and strain state at fracture and compare these results with those of Bridgman and other calculators. Our calculated neck stress shows monotonically decreasing stress in the radial direction and does not show the sharp stress peaks on the axis or the rounder stress peaks off the axis that these earlier calculations show. We find considerable differences from the Bridgman solution. An iterative computer method is introduced to allow correction of simple tension-test data to a universal flow-stress curve valid for large strain.

Effects of titanate coupling agents on the rheological and mechanical properties of filled polyolefins

Abstract: An experimental study was carried out to investigate the effects of titanate coupling agents on the rheological properties of p articulate-filled polyolefin melts. Inorganic fillers used were CaCO3, talc, and fiberglass, and polyolefins used were high-density polyethylene (HOPE) and polypropylene (PP). It was found that the addition of the coupling agent TTS to the PP-CaCO3 and PP-fiberglass systems reduced the melt viscosity considerably, whereas the addition of the coupling agent ETDS-201 to the PP-talc and HDPE-talc systems affected the melt viscosity very little. Also carried out was an injection molding study to investigate the effects of different inorganic fillers and the titanate coupling agents used on the mechanical properties of the injection molded specimens. It was found that addition of titanate coupling agents generally resulted in reduced modulus and tensile strength, and increased elongation and impact strength of the filled systems. The PP-CaCO3-TTS and HDPE-talc-ETDS 201 systems were found to have impact strength improved by approximately 100 percent with the addition of a titanate coupling agent. The PP-CaCO3-TTS samples have ultimate tensile elongation approaching that of virgin PP.

Characterization of self-curing acrylic bone cements.

Abstract: Four self-curing acrylic bone cements were surveyed by infrared, solubility, viscometry, quantitative metallography, microscopy, and physical testing techniques: CMW, Palacos R, Sulfix-6, and Surgical Simplex P. Results show that these bone cements were primarily composed of poly(methyl methacrylate) and that no cross-linking was evident. Solubility analysis confirmed this latter observation, as the bone cements dissolved completely except for a small insoluble fraction, which was identified as the radiopaque filler. For each bone cement, the viscosity-average molecular weights of both the powdered phase and the cured two-phase product remained unchanged, varying overall from 1 to 5 × 105. Using standard quantitative metallography, porosity ranged from 1 to 8% and the dispersed powder phase decreased 11–46%. Microscopy revealed the nature of the porosity, radiopaque fillers, the powder size and shape, and the fracture morphology. From tensile and fracture toughness tests, five physical properties were determined at ambient conditions and at 37°C after conditioning in distilled water at 37°C for 10 months: the modulus of elasticity, the ultimate tensile strength, the elongation at break, the fracture energy, and the mean inherent flaw size. At ambient conditions, the ultimate tensile strength decreased 33–55% when compared with commercial unmodified poly(methyl methacrylate), Plexiglas G. While the fracture energy remained rather invariant, the mean inherent flaw size increased fivefold over the commercial acrylic tested. This marked increase in the mean inherent flaw size could lower the fatigue resistance of a material, since more and/or larger fracture initiation sites are available. When tested at 37°C after protracted conditioning, the deleterious trends observed at ambient temperature continued. To some degree, porosity, particle-matrix interfaces, residual stresses, low molecular weight products, inorganic and/or other organic additions, and water contributed to the inherent flaw size at the expense of the working stress. Several modifications are suggested by which the importance of these factors might be minimized.

Effect of the curing cycle on some properties of a polymethylmethacrylate denture base material

Abstract: Summary The properties of a denture base material may be modified by altering both the temperature and the time of heating during the curing cycle. In this study a polymethylmethacrylate denture base containing no crosslinking agent was polymerised using four different curing cycles. The structure of the materials so obtained was investigated by an acid etching technique. The materials were characterized with respect to degree of cure, strength and water sorption. It was concluded that: 1. No correlation was observed between the curing cycles and polymer structure. 2. The curing cycle of 7 h at 70°C plus 1 h at 100°C produced best indentation strength and tensile strength. 3. A correlation was observed between residual monomer, indentation resistance, tensile strength and water sorption. This suggested that residual monomer concentration is the most important parameter in the determination of the properties of the material investigated in this study.

Tensile, impact and fatigue behavior of an amine‐cured epoxy resin

Abstract: Although crosslinked networks are commonly used as adhesives and composite matrixes, structure-property relationships are not as well established as with thermoplastics. For this reason, an extensive study was begun to systematically examine effects of stoichiometry, morphology, and distribution of crosslink density on viscoelastic behavior and ultimate properties. The system selected was based on a bisphenol-A-type epoxy cured with methylene dianiline. This paper describes and discusses results obtained for resins in which the amine/epoxy ratio ranged between 0.7 and 2.2. In agreement with reports by others, the tensile strength, modulus, and ultimate elongation were relatively insensitive to stoichiometry but did not show slight maxima or minima when the amine was somewhat in excess. Impact strengths, tensile energies-to-break and fracture toughness were, in contrast, quite sensitive, though the patterns of each differed significantly. Both fracture toughness and the stress intensity factor required to drive the crack at a given rate varied directly with the amine/epoxy ratio, as did estimates of the characteristic flaw size. Fatigue striations were observed on the fracture surfaces and corresponded to the incremental advance of the crack in one loading cycle.

The mechanical properties of zero- carbon ferrite-plus-martensite structures

Abstract: A study has been made of an Fe-3Ni-3Mo alloy whose structure can be either ferrite or martensite or any combination of ferrite plus martensite. By being able to measure the mechanical properties of the ferrite and martensite phases separately it is possible, using Milieko's theory for composites of two ductile phases, to calculate the properties expected for ferrite-plus-martensite mixtures. This theory assumes: 1) the stressstrain relationship for all structures is a power law; 2) a perfect interface between the phases; and 3) the fibers are aligned parallel to the stress axis. The experimentally determined tensile strength and ductility of the two-phase structures are in good agreement with the theory even though the martensite is not in the form of aligned fibers. The ductilities obtained at tensile strengths greater than 620 MPA (90 ksi) are no better than those for conventional HSLA steels because of the low ductility of the ferrite and low strength of the martensite.

The strength of multilayer and repaired composite resin.

Abstract: Composite resin surfaces that formed against a plastic matrix or that polymerized while exposed to air were excellent substrates for the adhesion of new resin. Samples formed by the addition of composite resin to a cut surface had a tensile strength of one half of the cohesive strength of the resin. Coating the cut surface with a thin layer of unfilled resin enhanced bonding of the second composite resin layer. The use of a thin layer of unfilled catalyst resin as a bonding agent caused the most rapid development of strength and the greatest strength in samples tested after 7 days.

Effects of dynamic strain aging on the subsequent mechanical properties of carbon steels

Abstract: Five carbon steels, AISI 1008, 1020, 1035, renitrogenized 1010 and 1522, were dynamically strain aged in the temperature range 100 to 600°C (373 to 873 K), with strains from 3 to 9 pct and strain rates from 2 × 10-4 to 2 × 10-2/s. Following this, changes in tensile, notch impact and fatigue properties were determined. The data obtained indicate that for a commercial combined straightening and strengthening operation on the cooling beds of a bar mill, the temperature during straining should be between 200 and 400° C, the strain should be less than 5 pct and the strain rate is unimportant, up to at least 10-1/s. After such treatment the tensile properties will be: Open image in new window

Evaluation of the tensor polynomial failure criterion for composite materials

Abstract: A comprehensive experimental and analytical evaluation of the tensor polynomial failure criterion was undertaken to determine its capability for predicting the ultimate strength of laminated composite structures subject to a plane stress state. Results are presented demonstrating that a quadratic formulation is too conservative and a cubic representation is required. Strength comparisons with test data derived from glass/epoxy and graphite/epoxy tubular specimens are also provided to validate the cubic strength criterion.

Compressive strength and ultimate strain of concrete under impact loading

Abstract: SYNOPSIS A drop-hammer test has been used to measure the compressive strength, ultimate strain, energy absorption and deformation modulus of concrete cubes under impact loading. By assuming a trapezoidal function for both the hammer impact pulse and the cube impedance function, hypothetical load and strain records have been derived which are similar to the initial experimental records measured on an oscilloscope. Concretes with varying mix proportions and two different coarse aggregates were examined and the results for compressive strength and ultimate strain are reported.

Evaluation of a Fundamental Approach for the Statistical Analysis of Fracture

Abstract: Generalized relations between the strength distribution function and derivatives of the fracture probability are developed for five widely used testing methods for measuring the strengths of ceramic materials. The derived relations for three of these methods are used to analyze room-temperature fracture strength data for hot-pressed silicon nitride. Fracture of this material is shown to be controlled by internal flaws at strength levels up to and including the range where the tensile and flexural distributions overlap, but it is primarily surface-flaw-controlled toward the upper end of the flexural distribution.

Fracture of aluminium-coated carbon fibres

Abstract: A degradation in the ultimate tensile strength (UTS) of aluminium-coated carbon fibres was associated with the formation of a reaction layer of aluminium carbide during annealing treatments ⩾ 475° C for high tensile fibres (HT) and ⩾ 550° C for high modulus fibres (HM). It was established that for a given annealing treatment, the UTS depended on the square root of the original coating thickness and proposed that fracture was controlled by cracks in the aluminium carbide, with a specific surface energy (γ) and intrinsic crack length (c0) of 2.33 J m−2 and ∼ 30 nm for HT fibres, and of 0.64 to 0.77 J m−2 and ∼ 20 nm for HM fibres.

High-strength optical preforms and fibers with thin, high-compression outer layers

Abstract: High-strength optical preforms and optical fibers, particularly useful in light-wave communication systems, are fabricated by techniques producing high surface compressive forces in thin outer layers. These result in substantially increased fiber tensile strength, durability, and fiber life. High surface stresses are achieved in three-layer and four-layer preforms and fibers by employing particular combinations of core, cladding, and layer compositions, dopants, coefficients of thermal expansion, and glass transition temperatures. Various suitable manufacturing methods are disclosed using chemical vapor deposition techniques. For example, preforms may be fabricated by external deposition of layers on a drawn core-glass rod, or by internal CVD methods in which layers are sequentially deposited within hollow tubular silica substrates that are then collapsed into solid preforms by known techniques. In the internal deposition methods, preform finishing techniques are also disclosed for removing excess substrate material so as to leave a high-strength compressive layer of substantially pure silica.

Superdrawn filaments of polypropylene

Abstract: Filaments of polypropylene having remarkably high strength and modulus have been prepared by the two-stage drawing process of Clark and Scott (4). In the first stage, un-oriented extruded billet is rapidly drawn to the natural draw ratio of ca 7X in hot silicone oil. The second stage of draw, a post neck draw process termed superdrawing, requires a slow rate of draw at carefully controlled temperatures to achieve maximum property values; the optimum conditions appear to be close to 4 percent/min at 130°C, The highest mechanical properties obtained were a Young's modulus of 22 GPa (240 gdtex, 3 × 106 psi) and a tensile strength of 0.93 GPa (10 gdtex, 1.3 = 105 psi) with an elongation to break of 7 percent. The filaments show a distinctive dead bend lack of recovery, WAXS data indicate high orientation of the molecules. SAXS data show no scattering to a resolution of 40 nm which is interpreted in terms of a continuous crystal matrix in the superdrawn filament. SEM micrographs of fractured filaments reveal a morphology of large fibrils of lath like habit with a thickness of ca. 0.1 μm. A series of experiments relating mechanical properties to the rate and temperature of superdrawing is interpreted in terms of two competing mechanisms; shearing displacement of microfibrils and unfolding of chain-fold blocks. Models are offered to explain the observed mechanical and physical property changes on superdrawing.

A new biodegradable plastic made from starch graft poly(methyl acrylate) copolymer

Abstract: A starch graft poly(methyl acrylate) copolymer was developed having grafted side chains with molecular weight of less than 500,000. This material can be easily extruded into a film which shows excellent initial tensile strength and elongation. Tensile strength, however, falls off rapidly after 70 hr of water immersion at 25°C. Starch graft poly(methyl acrylate) films show excellent susceptibility to fungal growth, some samples losing more than 40% of their weight after 22 days of incubation with Aspergillus niger. Tensile tests and scanning electron micrographs of the incubated samples, after being freed of mycelium, indicate substantial biodegradation of the starch portion of the copolymer. This material may have application as a biodegradable plastic mulch.

Strength Distribution of a Unidirectional Fiber Composite

Abstract: Three existing strength criteria for composite materials have been ex tended to account for the statistical behavior of ultimate strength of glass- epoxy composites. The basic distribution functions for the longitudinal, the transverse and the in-plane shear strengths were obtained by fitting the experimental data into a two-parameter Weibull distribution. These three functions were then used to predict the strength distribution of the com posite under off-axis loads. Theoretical and experimental results were com pared and discussed.