Showing papers on "Ultimate tensile strength published in 1969"

On the ductile enlargement of voids in triaxial stress fields

Abstract: The fracture of ductile solids has frequently been observed to result from the large growth and coalescence of microscopic voids, a process enhanced by the superposition of hydrostatic tensile stresses on a plastic deformation field. The ductile growth of voids is treated here as a problem in continuum plasticity. First, a variational principle is established to characterize the flow field in an elastically rigid and incompressible plastic material containing an internal void or voids, and subjected to a remotely uniform stress and strain rate field. Then an approximate Rayleigh-Ritz procedure is developed and applied to the enlargement of an isolated spherical void in a nonhardening material. Growth is studied in some detail for the case of a remote tensile extension field with superposed hydrostatic stresses. The volume changing contribution to void growth is found to overwhelm the shape changing part when the mean remote normal stress is large, so that growth is essentially spherical. Further, it is found that for any remote strain rate field, the void enlargement rate is amplified over the remote strain rate by a factor rising exponentially with the ratio of mean normal stress to yield stress. Some related results are discussed, including the long cylindrical void considered by F.A. McClintock (1968, J. appl. Mech . 35 , 363), and an approximate relation is given to describe growth of a spherical void in a general remote field. The results suggest a rapidly decreasing fracture ductility with increasing hydrostatic tension.

Behavior of Concrete Under Biaxial Stresses

Abstract: EXPERIMENTAL STUDIES INTO THE BIAXIAL STRENGTH OF CONCRETE ARE REVIEWED AND TECHNICAL DIFFICULTIES ENCOUNTERED IN THE DEVELOPMENT OF A SUITABLE TEST SETUP ARE DISCUSSED. A NEW TESTING APPARATUS IS DESCRIBED WHICH ALLOWS TESTING OF CONCRETE SPECIMENS UNDER VARIOUS BIAXIAL STRESS STATES. RESULTS OF AN INVESTIGATION FOR WHICH THIS EQUIPMENT WAS USED ARE REPORTED. THE TEST DATA INDICATE THAT THE STRENGTH OF CONCRETE UNDER BIAXIAL COMPRESSION IS ONLY 16 PERCENT LARGER THAN UNDER UNIAXIAL COMPRESSION. TESTS IN THE REGION OF COMBINED COMPRESSION AND TENSION CONFIRMED PREVIOUSLY OBTAINED DATA. THE BIAXIAL TENSILE STRENGTH OF CONCRETE IS APPROXIMATELY EQUAL TO ITS UNIAXIAL TENSILE STRENGTH. /ACI/

Adhesion of viscoelastic materials to rigid substrates

Abstract: Measurements have been made of the forces required to peel a thin layer of a model visco-elastic adhesive off a rigid substrate. Over a wide range of temperature and rate of peel the results were found to yield a single master relation in terms of peel rate when reduced to a reference temperature by means of the Williams, Landel & Ferry rate–temperature equivalence for viscous materials. The relations obtained were complex, however, with two main features: a cohesive–adhesive failure transition at low rates and a sharp decrease in peel strength at high rates. The first effect is shown to be due to a change in the deformation process in the adhesive, from a liquid-like to a rubber-like response. An approximate relation between peel strength and the tensile stress–strain behaviour of the adhesive is developed in terms of a single empirically-determined parameter, the interfacial bond strength. Values of this parameter are deduced for several substrates. Measurements of peeling under hydrostatic pressure showed that cavitation of the adhesive did not occur in these experiments. The second effect is shown to be due to the transition from a rubber-like to a glass-like response of the adhesive. It is also shown to depend on the way in which separation is effected. Some general principles governing the mode of failure and the development of maximum peel strength are outlined.

Strength of Concrete Filled Steel Tubular Columns

Abstract: The ultimate strength of axially and eccentrically loaded steel tubular columns covering a wide range of slenderness ratios was investigated. Hollow steel tubes were tested and compared with concrete filled steel tubes. It was found that the buckling load of the axially loaded long columns can be accurately predicted by summing the tangent modulus loads for the steel tube and the concrete core acting as independent columns. The effect of slenderness ratio on the lateral pressure exerted by the tube on the concrete was examined. Lateral pressure is exerted when the concrete commences to increase in volume at high strains and results in an increase in strength of the concrete. Buckling will occur before the longitudinal strain becomes sufficiently high to cause the concrete to increase in volume. For eccentrically loaded columns constructed from steel tubes infilled with concrete, it was found that a straight line interaction formula using the ultimate axial load and the ultimate flexural capacity of the sections predicted failing loads.

A Method of Predicting the Nonlinear Behavior of Laminated Composites

Abstract: This paper presents an analytical technique for determining the stress-strain response up to ultimate laminate failure for a laminated composite consisting of orthotropic lamina with nonlinear stress-strain behavior. The procedure, which has been programmed for a digital computer, will produce a laminate stress-strain curve up to ultimate failure. The technique is restricted to the prediction of ultimate strength for plane anisotropic laminates with midplane symmetry sub jected to biaxial membrane loads. Comparisons are made between analytical predictions and experimental results. The basic concepts of ultimate and limit strength design as applied to an advanced com posite structure are discussed.

Hydraulic Fracturing in Porous-Permeable Materials

Abstract: Extensive laboratory tests have been conducted to study hydraulic fracturing initiation in porous-permeable materials under open-hole conditions. Hydrostone specimens containing a vertical central hole simulating a well bore were subjected to unequal 3-dimensional compressive loadings, parallel and perpendicular to the hole axis. Fractures due to internal pressurization of the model well bore were always tensile ruptures. Initiation pressures were close to values predicted theoretically for porous-permeable materials. Fractures were always either vertical, normal to the smaller horizontal compressive load, or horizontal initiated close to the end of the packed-off region. Three pressurizing rates (6 psi/sec, 60 psi/sec, 600 psi/sec) were tested on hydrostone 32/100, cubical samples. The resulting critical pressures were clearly dependent upon the rate of pressurization, in accordance with theories of strength which show an inverse relationship between the time a load is applied to a sample and its tensile strength. (13 refs.)

Strength of Discontinuous Rocks in Direct Shear

Abstract: Synopsis The strength of discontinuous rocks under direct shear loading is examined analytically and experimentally. In the direct shear test a homogeneous and isotropic block of rock may fail by three mechanisms: failure in tension, failure in shear and failure at ultimate strength. The strength parameters include the tensile strength, fundamental shear strength (cohesion), angle of internal friction, the angle of friction at ultimate strength and the normal stress on plane of enforced shear. The direct shear strength of planes of weakness, orientated in the plane of enforced shear, is derived from two sources: strength of solid rock where no separation exists and joint friction along the separated parts of the shear surface. Maximum shear strength develops only if solid strength and joint friction are mobilized simultaneously, that is at the same deformation. On examine analytiquement et experimentalement la resistance de roches discontinues soumises a une charge de cisaillement direct. Dans un essai de...

Nonwoven polypropylene mats of increased strip tensile strength

Abstract: THE STRIP TENSILE STRENGTH OF NONWOVEN MATS OF POLYPROPYLENE FIBERS HAVING A DIAMETER FROM ABOUT 1 TO ABOUT 10 MICRONS IS INCREASED, FOR EXAMPLE, TO STRENGTHS GREATER THAN 4000 M., BY FUSE-BONDING, AS BY CALENDERING OR POINT-BOILING, AT LEAST A PORTION OF THE FIBERS OF THE MAT AT TEMPERATURES WITHIN THE RANGE FROM ABOUT 250*F. TO ABOUT 325*F., PREFERABLY, FROM ABOUT 280*F. TO ABOUT 315*F., WHILE THE MAT IS SUBJECTED TO PRESSURE SUFFICIENT TO PREVENT SHRINKAGE OF THE FIBERS IN THE MAT.

The tensile strength and ductility of continuous fibre composites

Abstract: The plastic instability approach has been applied to the tensile behaviour of a continuous fibre composite. It is shown that the combination of two components with different strengths and degrees of work-hardening produces a new material with a new degree of work-hardening, which may be determined by the present analysis. Expressions for the elongation at rupture and the strength of a composite have been obtained and the results of the calculation are compared with some experimental data.

Effects of Hydrostatic Pressure on the Mechanical Behavior of Polyethylene and Polypropylene

Abstract: An apparatus has been designed and constructed that will allow determination of the mechanical behavior of polymer specimens subject to applied tensile and compressive loading, while the sample is simultaneously subject to a hydrostatic pressure environment. The moduli of high‐density polyethylene and polypropylene determined from compressive tests show a significant increase with pressure. Tensile nominal stress‐strain curves have been obtained at various pressures up to 100 000 psi. These show that the yield stress also increases significantly with increasing pressure for both materials. The nature of yielding and fracture is found to be quite different for the two polymers studied. Polyethylene tends to deform more by shear, and the necked region at high pressures reduces to a fine point before separation. In polypropylene, fracture occurs by plastic tearing across the cross section. An attempt is made to account for the experimental results by use of yield criteria that includes a hydrostatic pressure...

Shear Strength of Reinforced Concrete Beams

Abstract: The stress distribution at failure and the failure modes of reinforced concrete beams with and without web reinforcement failing by shear-compression have been investigated Stress redistribution which takes place at the diagonal tension cracking load is caused by internal local rotation, which increases the width of the diagonal tension cracks The crack width is proportional to the distance from the center of rotation at the apex of the diagonal tension crack The ultimate strength of beams failing by shear-compression is dependent on the location of the diagonal tension crack within the compression zone, and the shear span ratio The diagonal tension crack is located at the center of the compression zone

The effect of antiplasticization on secondary loss transitions and permeability of polymers

Abstract: Antiplasticizers are considered to be diluents which when added to polymers result in mechanical property behavior opposite to that of plasticization. The addition of antiplasticizers to certain polymers such as Bisphenol A polycarbonate, polysulfone, and polyvinyl chloride results in the elimination of the secondary loss transitions of these polymers. As a drop in modulus accompanies these transitions, their elimination results in higher tensile strength and tensile modulus. As secondary transitions are commonly associated with ductility and impact strength, their elimination also results in the observed embrittlement characteristics. The addition of anti-plasticizers to polymers also restricts the diffusion of penetrants resulting from the decrease of molecular flexibility in the polymer matrix.

Low endurance fatigue in metals and polymers

Abstract: Studies of crack growth in fatigue of annealed aluminium, Nylon 66 and Araldite epoxy resin have revealed two mechanisms, shear and tensile tearing. The former applies both to fatigue and to tensile straining under approximately plane strain conditions and requires a capacity for plastic flow within the material. The latter mechanism occurs where flow is either restricted or impossible. A model for crack propagation in low endurance fatigue is described, and a rigid-plastic analysis is shown to be consistent with the observations.

Bearing Capacity of Concrete Blocks or Rock

Abstract: The limit theorems of the generalized theory of perfect plasticity are applied to obtain bearing capacity in two dimensions (strip loading or rigid punch) and in three dimensions (circular and square punches). With the safe assumption that concrete or rock is unable to take any tension, the bearing capacity is shown to be just the unconfined compressive strength of the column of material directly under the load. When a small but significant tensile strength is assumed, along with the Mohr-Coulomb surface for failure in compression taken to represent a perfectly plastic yield surface, the predicted capacity is found to be in good agreement with published test results. The influence of friction in this class of problems is also analyzed as is the limited applicability of so drastic an idealization of the real behavior of a material as brittle as concrete or rock.

Hydrogen Embrittlement of Type 304L Stainless Steel

Abstract: The ductility of Type 304L and Type 310 stainless steel as measured by tensile elongation can be reduced substantially when high contents of hydrogen are absorbed. Cathodic charging of thin stainless steel foils severely reduced the foils' ductility and tensile strength. Only a very thin surface layer was damaged by cathodically charged hydrogen because the hydrogen diffused very slowly into the metal, the relative loss of ductility caused by cathodic charging of cold worked material depended on the amount of martensitic phases present. The maximum relative loss of ductility was in material that had been cold strained at −196 C (−320 F) and contained large amounts of the martensitic phases (alpha prime, body-centered cubic and epsilon, hexagonal close-packed). The loss of ductility was related to the width and depth of surface cracks observed in mechanically tested hydrogenated material.

Double punch test for tensile strength of concrete, Sept. 1969 (70-18) PB224770/AS (NTIS)

Abstract: This paper describes a new test technique for determining the tensile strength of concrete. In this test, a concrete cylinder (or cube) specimen is placed vertically between the loading platens of_a testing machine and compressed by two steel punches located concentrically on the top and bottom surfaces of the cylinder (or cube) . The relevant formula for computing the tensil,e strength in the new test is herein developed using the theory of perfect plasticity. It is shown that the necessary test arrangement, as well as the formula for computing the tensile strength of concrete, are very simple. The new test appears promising for practical use. * Assistant Professor, Fritz Engineering Laboratory, Department of Civil Engineering, Lehigh University, Bethlehem, Pennsylvania.

Package of composite film with peelable, heatsealable surfaces

Abstract: A package comprised of a composite, peelable, heatsealable thermoplastic film having at least two layers, said film having a heatseal strength of less than about 1.0 pound per inch width. The low heatseal strength is achieved by an outer thermoplastic layer having a caliper of less than about 0.4 mil, the outer layer being characterized in having a tensile strength of less than about 10,000 psi and having an interlaminar steel strength of the outer layer to the molecularly different other layer of less than about 1.0 pound per inch width. Numerous combinations of thermoplastics may be employed for the outer and other layers.

Mechanical properties of glass fibre-reinforced gypsum

Abstract: Gypsum plaster, like other inorganic cements, is strong in compression but weak in tension exhibiting brittle behaviour. Commercialy available E glass fibres can be used to reinforce the gypsum plaster matrix and produce a strong composite material having improved tensile and impact properties. This paper describes the effect of glass content on the flexural, tensile, compressive and impact strength of this glass fibre plaster composite which is made by a simple spray/suction technique.

Mechanical properties of rocks

Abstract: CONTENTS: SCIENTIFIC RESEARCH RESULTING IN A PROPOSAL FOR AN INTERNATIONAL STANDARD ON TESTING ROCKS UNDER UNIAXIAL COMPRESSION AND SHEAR WITH COMPRESSION EFFECT OF ACCURACY IN ROCK-SPECIMEN PREPARATION ON THE RESULTS OBTAINED EFFECT OF DIMENSIONS ON TENSILE AND SHEARING STRENGTH ANALYSIS OF AN INTERNATIONAL SURVEY AIMED AT THE DEVELOPMENT OF EQUIPMENT FOR TESTING ROCKS UNDER TRIAXIAL COMPRESSION A NEW COMBINED METHOD OF ROCK TESTING FOR TENSILE, COMPRESSION AND BENDING STRENGTH, IN WHICH THE SAME SPECIMENS ARE USED REPEATEDLY TEST RESULTS OBTAINED BY THE ABOVE METHOD FOR A NUMBER OF BEDROCKS IN COAL AND ORE DEPOSITS CHANGES IN ROCK PROPERTIES OBSERVED IN THE ZONE OF CONTACT WITH TOOLS, ON WHICH A METHOD OF ASSESSING BRITTLENESS AND PLASTICITY FROM CHANGES IN HARDNESS (UNDER INDENTATION OF IMPACT) IS BASED A PROPOSAL FOR IMPROVING HARDNESS TESTING OF ROCKS CONTAINING SEVERAL MINERALS, BY DETERMINING THE CONTENT AND HARDNESS OF EACH INDIVIDIDUAL MINERAL EFFECT OF PHYSICAL AND MECHANICAL ROCK PROPERTIES ON DRILLABILITY, AS ANALYZED IN MANY YEARS OF RESEARCH. /LCPC/RRL/

The mechanical properties of single crystals of pure ice

Abstract: Results obtained from tensile and compressive tests on pure ice single crystals at various temperatures down to −90°C are reported. At −50°C tensile creep tests give a continually increasing creep rate until fracture, as observed at higher temperatures. The stress dependence of the strain-rate is discussed. Fracture stress increases with decreasing temperature. Results from constant strain-rate compressive tests are compared with theoretical curves computed from Johnston’s (1962) theory of dislocation multiplication. A dislocation velocity of the order of 0.5×10−8 m s−1 is deduced for ice at −50°C.

The Effect of Silicon on the Stress Corrosion Resistance of Low Alloy High Strength Steels

Abstract: The effect of five levels of silicon, within the range 0.09% to 2.15%, on the stress corrosion resistance of 4340 steel was established in 3.5% sodium chloride solution for two tensile strength ranges (280 to 300 ksi and 230 to 240 ksi). At the higher strength range, the threshold stress intensity KISCC was independent of silicon content, but the stress corrosion crack velocity was significantly retarded when the silicon content exceeded 1.5%. At the 230 to 240 ksi strength range, steels containing less than 1.5% silicon exhibited a higher KIscc threshold than steels of higher silicon content. Strength level had a significant effect on crack velocity characteristics.

High-strength structural blind fastener for use in airplanes, rockets and the like

Abstract: A three-part high-strength structural-type blind fastener of the bolt- and nut-type, the parts of which are made of high-strength material and have a structural design relationship which provides in the fastener higher tensile and shear characteristics and improved clamp up characteristics.

Folded chain model of highly drawn polyethylene

Abstract: Neither the fringed-micelle, fringed-fibril or extreme folded-chain models explain the morphological and mechanical properties of highly drawn polyethylene. The modified folded-chain model, assuming that a substantial fraction (between 5 and 30 percent) of the molecules do not fold back at the crystal surface but go through the “amorphous” surface layer and enter the next crystal, avoids the insufficiencies of the above mentioned models. The elastic modulus and tensile strength of drawn polyethylene, both increasing with draw ratio, are to a large extent the consequence of the molecules bridging the quasi-amorphous layers and interconnecting the folded-chain lamellae oriented more-or-less perpendicular to the machine direction. The folds create enough space for the accommodation of more-or-less extended tie molecules in the quasi-amorphous layers between the lamellae. Electron microscopy and calorimetry of samples as drawn, annealed and/or etched with fuming nitric acid support the model.

Strain‐Rate Dependence of the Tensile Failure of a Polycrystalline Material at Elevated Temperatures

Abstract: A general discussion is presented of the failure modes which can occur in uniaxial tensile tests of a polyphase, polycrystalline material at various strain rates at elevated temperatures. Specific results in the temperature range 0.56–0.70Tm are given using Type 316 stainless steel as a representative material. The intrinsic plastic failure is determined solely by plastic deformation, leading first to necking and concluding by separation at a point. However, this intrinsic plastic failure may be interrupted at relatively high strain rates by the formation of cracks at inclusions within the neck. At low strain rates the onset of appreciable necking is postponed and the whole failure process is determined by intergranular crack formation. At intermediate strain rates intergranular cracks form within the neck, and a shear mode of failure is possible. Some conclusions regarding future studies are included.