Showing papers by "Lehigh University published in 1971"

Stress singularities in a two-material wedge

Abstract: A method for the determination of stresses in a two-material wedge-shaped region is presented. The method is applicable for plane strain or plane stress problems and treats the general case where each region is a wedge of arbitrary angle. The results are obtained by the use of the Mellin transform and the theory of residues. The characteristic equation is investigated to determine the stress singularity resulting from certain combination of geometry and material properties. A formal solution is then presented for the case where the loading is in the form of a point dislocation along the interface. This solution is the Green's function for the more general mismatch problems and therefore has applications in solving other problems with compatible boundary conditions. The results obtained show that for small values of r the dominant effect is due to geometry and the secondary effect is caused by the choice of elastic constants of the materials.

Shear strength of stud connectors in lightweight and normal weight concrete, AISC Eng'g Jr., April 1971 (71-10)

Abstract: STEEL-CONCRETE composite construction using normalweight concrete has been used since early in the 1920's. Substantial use of composite construction began mainly for bridge structures in the 1950's as a result of the work done by Viest. 16-18 Its primary growth in building construction during the last decade was a result of the simplified design provisions introduced into the 1961 AISC Specification. The development of these provisions were based on studies reported by Slutter and Driscoll. 5,11 The type of shear connectors has changed substantially during the past 20 years. Bridge construction made extensive use of spiral connectors in the early 50's. These were replaced by the flexible channel and stud connectors. Today, headed studs are used extensively for both bridge and building construction. The first studies on stud shear connectors were undertaken by Viest, who tested full scale pushout specimens with various sizes and spacings of the studs. 16 Later studies on bent and headed studs were initiated at Lehigh University by Thurlimann. 15 A series of beam and pushout tests were reported by Slutter and Driscoll, who developed a functional relationship between the shear connector strength and the concrete compressive strength. 5,11 The mathematical model was comparable to the useful capacity proposed earlier by Viest. 17

Mortality and Coronary Heart Disease Among Men Studied for 23 Years

Abstract: Twenty-year coronary heart disease (CHD) incidence is analyzed for 279 men, CHD-free at the ages of 47 through 57 years and characterized by three examinations before 20 annual follow-up examinations. Sixty men developed CHD, 42 dying or suffering infarction. Among 20 entry characteristics, three had major predictive power, especially for CHD death or infarction: cold pressor test, a high level of serum cholesterol, and systolic blood pressure. Smoking and relative weight seemed unimportant. Major CHD incidence was proportional to cholesterol to the 3.4 power. Five-variable multiple logistic analysis permitted placement of men into deciles of estimated risk differing more than tenfold in CHD incidence. The combination of only cholesterol and systolic pressure was nearly as good. The multiple logistic coefficients applied to five-year data on 1,287 men among whom 182 CHD developed in 182 yielded satisfactory agreement between observed and predicted distributions of CHD cases in classes of estimated risk.

The morphology of martensite in iron alloys

Abstract: Light and electron microscopy have been used to determine the main structural differences between the two major types of martensite in ferrous alloys. In the martensite that forms in dilute alloys of iron, the basic transformation unit takes the shape of a lath, and hence the term lath martensite is appropriate for identifying this morphology. Each lath is the result of a homogeneous shear, and successive shears produce a packet of parallel laths containing a high density of tangled dislocations. The other type, plate martensite, differs in the shape taken by a transformation unit and its transformation sequence is characterized by nonparallel plate formation. Investigation of a large number of binary ferrous systems shows that alloy composition and the transformation temperature influence the transition from lath to plate martensite. These two factors are discussed in terms of their possible effects on the plastic deformation mechanisms which must occur in the parent austenite and product martensite during transformation.

Stress Distribution in Bonded Joints

Abstract: Stress distribution in plates and tubes bonded by stepped joints, assuming generalized plane stress

Nonlocal continuum mechanics

Abstract: : It is shown in this paper that the conservation laws of nonlocal continuum mechanics are equivalent to, and can be derived from, the conservation of energy and the invariance conditions under superposed rigid body motions. Also, the theory of nonlocal thermoelasticity is reconsidered in the light of recent developments in thermodynamics, taking invariance conditions fully into account. (Author)

Homogeneity range and the martensitic transformation in TiNi

Abstract: It is shown that the structure homogeneity range of the B2 TiNi compound is very restricted below 500°C. A new phase, containing 58 at. pct Ni and structurally related to Ni3Ti, forms peritectoidally at 625° ± 20°C. The precipitation in nickel-rich TiNi is very slow, and a metastable, supersaturated B2 structure can be readily retained. At equilibrium the martensitic transformation takes place at ∼60°C, independent of the overall composition. Quenching from 600°C and above raises the transition temperature in titanium-rich, and lowers it markedly in nickel-rich compositions. The resulting martensite structure in the latter is also believed to change with increasing the prior anneal temperature. The observations reported previously on the transformation behavior must be considered as obtained on nonequilibrium, metastable materials, which may account for the discrepancies in the observed property variation. Close control of the processing variables is necessary to ensure reproducibility, particularly if nonequilibrium transformation behavior is desired.

A review of the three-dimensional stress problem for a cracked plate

Abstract: An analytical study has been carried out to examine the influence of plate thickness on the stress distribution around the crack. The qualitative feature of the three-dimensional solution is first determined by an asymptotic expansion of the stresses and displacements in terms of the cylindrical polar coordinates r, θ, z for small values of r which is referenced from the border of a semi-infinite crack. It is found that the stresses σrr, σθθ, σ zz , and σ rθ are singular of the order r $$r{\text{ }}^{{\text{ - }}\tfrac{1}{2}} $$ , but the transverse shear stresses σ rz and σθz , are bounded for plates under stretching and bending. The intensity of crack-border stress field becomes a function of the thickness coordinate z. Knowing that the problem prohibits any exact analytical solutions of a quantitative nature, the three-dimensional equations of elasticity will be approximated by appealing to minimum principles in the calculus of variations. Guided by the results obtained from the asymptotic expansions, each one of the six stress components is assumed to be the product of two functions, one being assigned to describe the stress distribution in the plane of the plate and the other across the thickness. The z-distribution of the stresses may either be pre-assigned arbitrarily or determined from the plane strain condition ahead of the crack. On the basis of the principle of minimum complementary energy, a system of three simultaneous differential equation in two variables is obtained and solved for the problem of an infinite plate containing a through crack by means of integral representations. Determined in closed elementary form are the detailed structure of the three-dimensional crack-edge stress field. The stress-intensity factor, which varies in the thickness direction, is shown to be a function of the ratio of plate thickness to crack length and is found to increase rapidly in magnitude as the plate thickness is perturbed slightly from zero. The present analysis suggests a method by which the effect of a finite plate thickness can be incorporated into an examination of the fracture toughness of cracked sheet specimens.

Delay Effects in Fatigue Crack Propagation

Abstract: The fatigue crack propagation behavior resulting from variations in load is examined for 2024-T3 aluminum alloy, from both a macroscopic and a fractographic point of view. A peak load is found to cause retardation of the crack growth rate, which becomes more pronounced as the percentage overload or baseline stress intensity level or both is increased. The delaying effect of the overload is observed to exist for a calculated crack length increment equivalent to the plastic zone size formed during the peak load. Multiple overloads and high-low block loading sequences are found to result in additional retardation. It is observed that the macroscopic fracture surface appearance (that is, transition to plane stress) is a function of the crack growth rate. From fractographic examination it is found that the initiation of microvoid coalescence during fatigue occurs when plane stress conditions are achieved; this limits the extent of the stretch zone associated with an overload cycle. As a result, the stretch zone is found to be followed by striations in plane strain and by dimples under plane stress conditions. The size of the stretch band is observed to depend on the stress intensity level during the overload cycle. The usefulness of closure concepts in aiding the understanding of fatigue crack propagation under uniform and nonuniform loading conditions is considered. Evidence is given to demonstrate the general applicability of closure concepts for analysis of macroscopic and fractographic fatigue crack propagation results. /Author/

Dislocation arrays in Cu-Al alloys. I

Abstract: The dislocation arrangements in single crystals of Cu 2% at. Al and Cu 10% at. Al deformed into stage II of the work-hardening curve have been observed by transmission electron microscopy. The observations are described and discussed in relation to the theories of stage II work-hardening. It is concluded that the behaviour of Cu 2% at. Al is well described by the theory of Hirsch and Mitchell (1967) but that no theory exists to describe the stage II behaviour of an alloy such as Cu 10% at. Al deforming by planar slip. However, the main component of the flow stress in Cu 10% at. Al is the forest stress.

Reaction mechanisms for the coatings formed during the hot dipping of iron in 0 to 10 Pct Al-Zn baths at 450° to 700°C

Abstract: The reaction mechanisms and the structures of the phases formed during the hot dipping of iron in 0 to 10 pct Al-Zn alloy baths at temperatures of 450° to 700°C were studied by X-ray diffraction and electron microprobe analysis techniques. A new mechanism for the inhibition reaction between iron and zinc is proposed. At bath temperatures below 600°C, a thin layer of an Fe-Al-Zn ternary compound forms on the iron surface and inhibits the growth of Fe-Zn phases. Breakdown of inhibition occurs during the dipping process when the ternary compound becomes rich in aluminum and transforms to a more stable structure which is isomorphous with Fe2Al5. While this breakdown is occurring, the zinc atoms react with iron and form the conventional Fe-Zn phases.

Mode II Fatigue Crack Propagation

Abstract: Fatigue crack propagation rates were obtained for 2024-T3 bare aluminum plates subjected to in-plane, mode I, extensional loads and transverse, mode II, bending loads. These results were compared to the results of Iida and Kobayashi for in-plane mode I-mode II extensional loads. The engineering significance of mode I-mode II fatigue crack growth is considered in view of the present results. A fatigue crack growth equation for handling mode I-mode II fatigue crack growth rates from existing mode I data is also discussed.

The Problem of an Elastic Stiffener Bonded to a Half Plane

Abstract: The contact problem of an elastic stiffener bonded to an elastic half plane with different mechanical properties is considered. The governing integral equation is reduced to an infinite system of linear algebraic equations. It is shown that, depending on the value of a parameter which is a function of the elastic constants and the thickness of the stiffener, the system is either regular or quasi-regular. A complete numerical example is given for which the strength of the stress singularity and the contact stresses are tabulated.

An exploratory study of delay in fatigue-crack growth

Abstract: Compression, creep, stress relaxation and overloading effects on delay in fatigue crack growth and structural life predictions

Nonlinear Continuum Mechanics of Viscoelastic Fluids

Abstract: In the last twenty-five years there has been great progress in the development of nonlinear continuum theories in mechanics and other branches of physics, and in the use of such theories to explain and predict phenomena that cannot be explained rationally by the classical linear theories.

Measurements on the biaxial extension viscosity of bulk polymers: The inflation of a thin polymer sheet

Abstract: An experimental study of the inflation of a thin polymer sheet has been conducted to determine whether this technique can be used to measure the biaxial extensional viscosity of bulk polymers. Viscosities were determined at various extensional strain rates using two undiluted polyisobutylene samples having different molecular weights. Advantages, limitations, and errors associated with the method are discussed.

Limit analysis of stability of slopes

Abstract: THE UPPER BOUND THEOREM OF LIMIT ANALYSIS IS APPLIED TO OBTAIN COMPLETE NUMERICAL SOLUTIONS FOR THE CRITICAL HEIGHT OF SLOPES. A LOGARITHMIC SPIRAL MECHANISM WHERE THE FAILURE SURFACE MAY PASS BELOW THE TOE IS ASSUMED IN THE ANALYSIS. THE ANALYSIS INCLUDES THE EXISTING LIMIT EQUILIBRIUM SOLUTIONS AS WELL AS THE PREVIOUSLY OBTAINED LIMIT ANALYSIS SOLUTIONS AS A SPECIAL CASE, SO THAT IT MAY BE CONSIDERED A GENERALIZATION OF ALL THESE PREVIOUS SOLUTIONS. THE RESULTS FOUND ARE PRACTICALLY IDENTICAL TO THOSE OBTAINED BY THE EXISTING LIMIT EQUILIBRIUM PROCEDURES. /AUTHOR/