Influence Of Sheet Thickness Research Articles

On the Thickness Effect of Axisymmetric Deformation of Sheet Metals

In the present investigation, we have studied the influence of sheet thickness on the limiting strain, i.e., forming limit, of a mild steel by punch stretching experiments. Our results show that for a two-fold increase in thickness the limiting strain of a material does not substantially increase with increasing thickness of the sheet. These experimental observations were well supported by the results of theoretical analysis using Finite Element modelling of the process.

Effect of Grain anisotropy on limit strains in biaxial stretching: part i. influence of sheet thickness and grain size in weakly textured sheets

Processes of inhomogeneous deformation which lead to localized necking in biaxial stretching have been investigated in sheets of copper, Cu-30 pct Zn brass and low-carbon steels of good commercial quality without strongly developed preferred orientations. With sheet thickness,to, in the range 0.4 to 1.2 mm, it was found that limit strains in biaxial stretching decreased with decreasingto/do, wheredo is average grain diameter. It was concluded that, whento/do was less than about 20, plastic anistropy of individual grains of the primary phase was the dominant source of the strain inhomogeneities which developed to cause eventual necking failure. Measurement of the rate at which surface roughness developed with increasing strain,dR’/d- ge, indicated that, in the early stages of stretching, the growth of thickness inhomogeneity was close to being proportional todo and -ge and it was insensitive toto and the applied strain ratio, p, but, at an applied strain -gem which depended onto anddo, dR /d- ge started to increase progressively. In this latter phase of the process strain localization developed on a macroscopic scale. It is concluded that the dependence of -gem onto underlies the effects of sheet thickness on biaxial limit strains, also that the influence of p on the rate of growth of thickness inhomogeneities can change progressively during the evolution of strain localization through the microstructural and macroscopic phases.

The influence of sheet thickness on delayed retardation phenomena in fatigue crack growth in HT80 steel and A5083 aluminium alloy

Three types of delay tests were carried out on HT80 steel and A5083 aluminium alloy in order to investigate the differences in the retardation behavior of fatigue crack growth in the central and edge regions following a single application of an overload; the first type were tests on specimens of four different thicknesses, the second type were tests on specimens whose surface layers were machined away just after the overload, and the third type of test used variations in the loading to put beach-marks on the fatigue fracture surface. In the tests on the specimens of four different thicknesses, the retardation effect was almost constant in the predominantly plane strain region and increased drastically in the plane stress region for the steel, while it became a minimum at the transition from plane strain to plane stress for the aluminium alloy. Machining away the surface layers following the overload, in the type 2 tests, resulted in a drastic decrease in the retardation for the aluminium alloy, but had little influence on the retardation for the steel. The beach-marking tests revealed that the crack front was slightly curved before the overload was applied. Following the application of the overload the curvature initially decreased, and then increased until the retardation was over at the surface. Thereafter, the curvature decreased toward the equilibrium curvature characteristic of the preoverload fatigue conditions. This difference in retardation behavior between the surface and the interior was much larger in the aluminium alloy than in the steel. This behavior was explained theoretically on the basis of the test results both on the specimens of varying thicknesses and on the surface-removal specimens.

The Influence of Sheet Thickness and Heat Treatment on the Magnetic Properties of Hardperm Alloys in the Ni–Fe–Nb System

The Influence of Sheet Thickness and Heat Treatment on the Magnetic Properties of Hardperm Alloys in the Ni–Fe–Nb System

Absorbed energy during compression and crushing of high strength steel sheets

The absorbed energy(E a orE a′) in static and dynamic compression of the test specimens constructed from high-strength steel sheets, and the influence of the mechanical properties of the sheet steels, on the first buckling load(P max), were studied experimentally. The influence of sheet thickness and test specimen size onE a, Ea′, andP was also investigated. The following relations were obtained: In static compression: Pmax = 4.57(Σe =0.02)0.62 · t2.0 x 103 (N) E a = 79.4(Σe=0.02)0.84· t1.9 (J) and in dynamic compression:E a′=K·(ΣB)0.6 · t1.9 (J) Ea′/Ea decreases with increasing tensile strength of steel sheet, and approaches about 1.2 at above 400 N/mm2.

Determination of valid R-curves for materials with large fracture toughness to yield strength ratios

Crack growth resistance curves are derived from a generalised theory of quasi-static crack propagation due to Gurney and Hunt. Both the subcritical and continuous cracking regions are investigated, where the fracture toughness of the material may depend on the cracking rate, the reacting environment at the crack tip and the mode of fracture. Precise conditions for stability of the spreading crack relative to chosen constraints of either a displacement- or load-controlled machine are formulated. Cracking of sheet materials with high fracture toughness and low yield stress, (e.g. (K/σ y )2 > 200 mm), which do not satisfy certain size requirements, is often complicated by generalised yielding at regions remote from the crack tip. Complete R-curves for such materials cannot be established with conventional testpieces in the laboratory. The present paper adopts a new experimental technique [1] where a laboratory size reinforcement rig attached to the testpiece eliminates all irreversibilities caused by generalised yielding. Valid fracture toughness values and crack growth resistance curves are thereby determined, irrespective of the amount of elastic and plastic deformations occurring at the crack tip. Successful R-curve experiments are described for fracture in a few ductile and tough materials such as 7075-T3. and 1100-0 aluminium alloys, and a low carbon steel. Comparison is made with other published R-curves, and the influence of sheet thickness and (K 1c /σ y ) ratio on the geometry of R-curves is investigated. A simple relationship for R-curves is suggested, viz.: R = R 0 + (ΔL) p , where, it seems, R 0can be identified with the plane strain toughness (i.e. R 0 = G 1c = K 1c 2 /E(1 - v 2)1/2). A possible reason for this unexpected result is given in the paper. Useful estimates of K lcmay thus be available from thin sheet tests.

The Influence of Sheet Thickness on Crack Propagation

THE influence of the sheet thickness on fatigue‐crack propagation was studied on specimens of 2024‐T3 alclad sheet of five thicknesses, viz. 0.6, 1, 2, 3 and 4 mm. It turned out that cracks grow faster in thicker sheets. The different states of stress at the crack tip probably cause the thickness effect.