Showing papers on "Indentation published in 1976"

Indentation plasticity and the ensuing fracture of glass

Abstract: A systematic study of spherical indentations on various glasses has shown that for small indenters (

Statistical Determination of Surface Flaw Density in Brittle Materials

Abstract: The density of surface flaws in brittle materials can be determined from the loads in many different kinds of tests. A general method is derived and applied to indentation experiments on crown, plate, window, lead, and commercial heat-resistant and heat-absorbing glasses. Knowledge of flaw density is important for estimating size effect, and differences in flaw density indicate the possibility of significant improvements in strength by eliminating a few major sources of flaws.

Effects of Residual Stresses on Fracture from Controlled Surface Flaws

Abstract: RFracture tests were conducted on surface flawed Si/sub 3/N/sub 4/ bend specimens as function of surface removal Results show that residual stresses at the Knoop microhardness indentation affect fracture of the controlled surface flaw beneath the indentation Annealing was found to heal surface flaws and because of this, the relative contribution of residual stresses to the effects of annealing on the critical stress intensity factor in Si/sub 3/N/sub 4/ could not be assessed (JRD)

Rooted aerodynamic blade and elastic roll pin damper construction

Abstract: Herein disclosed is the combination of an aerodynamic blade having a root formed with outwardly curved shoulders and a transverse curved indentation, a rotor disc formed with a blade root receiving slot having curved complementary retaining surfaces in contact with those shoulders and an elastic split metallic roll pin disposed between the indentation and disc to provide damping, the radii of the curved shoulders and retaining surfaces being generated from an axis below said indentation.

Finite element analysis of indentation on glass

Abstract: The finite element method was applied to the analysis of the indentation process on glass. The calculated values of hardness for ideal elastic-plastic materials showed reasonable agreement with those obtained experimentally by other authors, but the calculated shapes of indentation were somewhat different from the real ones. When densification was taken into account, the calculated shapes of indentation showed better agreement with the real ones. The parameters for the calculation were estimated. The contribution of densification to the total deformation was estimated to be less than 45%, using the yield criterion as a basis for this estimation. A structure similar to the rosette-like structure was also calculated by this method. The finite element method was found to be one of the most effective methods for analysing indentations on glass, and it was shown that the mechanical properties of some glasses may be determined by precise observation of their indentations.

The indentation behaviour of hard metals

Abstract: The indentation behaviour of hard materials which deform plastically and also exhibit surface fracture is discussed. It is shown that both radial and circumferential fracture can develop around the indentation and that this can be explained in terms of a transition from elastic/plastic behaviour. In general the circumferential cracks form at lower loads but remain short and shallow, and their initiation is affected by the grain size of the material. Experiments with a hard spherical indenter showed that radial cracks in water-quenched EN44B steel develop at loads above approximately 40 F*, where F* is the applied load to cause the first plastic deformation. Residual stresses in the surface layers can cause these cracks to continue growing after load removal. Finally, an equation relating contact area and pressure is developed from earlier work of K L Johnson (1970) and it is shown that this gives good agreement with experiment.

Dependence of micro-indentation hardness on the superstructure of polyethylene

Abstract: The “Vickers” micro-indentation hardness of a series of melt crystallized polyethylene (PE), plastically deformed PE and melt crystallized paraffins was determined to establish correlations with superstructure, i. e. crystallite size, orientation and number of tie molecules. In 100% crystalline systems (paraffins) the penetration depth of the indenter is a hyperbolic decreasing function of crystal thickness,I, and extrapolates forl → ∞ to the experimentally indentation value obtained for high pressure crystallized PE (“extended chain crystals”). In the polymer case (two phase system) indentation depends on bothl and on amorphous content. Thus, for a givenl, PE shows, depending on crystallinity, higher indentation values than paraffins. The “amorphous” phase is related to the reversible loading time dependence of indentation which levels off to a characteristic limiting value. The time dependent behaviour of indentation vanishes either when the amorphous phase is removed by selective oxidative attack or when the polymer is plastically deformed at high deformations (λ>12) and the tie molecules in the amorphous layers and interfibrillar regions are highly strained. The change of microhardness as a function of draw ratio, λ, is discontinuous in support of the abrupt transformation from the original microspherulitic into the fibre structure according to the model of plastic deformation proposed byPeterlin (20, 21). The highly anisotropic fiber structure yields a conspicuously anisotropic shape of the indentation which can be explained by a recovery of the microfibrils parallel to the fibre axis. Finally, the increase of microhardness withλ, can be correlated to the increasing number of tie molecules in the fibrous structure.

High speed indentation of an elastic half-space by conical or wedge-shaped indentors

Abstract: Self-similar problems of indentation of an elastic half-space by rigid cones or wedges are solved, assuming perfect adhesion, when the velocity of indentation is large enough for the area of contact to spread faster than the speed of P-waves. In contrast to the earlier study of the wholly subsonic case [2], the present problems can be solved in closed form without approximation. It emerges, too, that the no slip condition would be satisfied for a range of values of a finite coefficient of friction, in contrast to the situation in [2], where any finite friction is bound to allow some slip. A variety of wave fronts exist in the present problems and all of their amplitudes are found explicitly and discussed.

Quasi-Static Solid Particle Damage in Brittle Materials.

Abstract: : This report is a three part study of indentation fracture in the plastic contact regime. The first part summarizes the observations of fracture and develops a fracture classification scheme. The second part discusses the implications of the fracture characterization for fracture toughness determinations, and abrasive wear and low velocity erosion prediction. Finally, the third part discusses indentation friction and its measurements, as needed to determine the role of friction in the indentation fracture process. (Author)

Two contact problems in anisotropic thermoelasticity

Abstract: Some basic equations recently derived by Clements are used to consider two contact problems in anisotropic thermoelasticity. The first problem concerns the determination of the thermal stress in an anisotropic half-space due to a heated load over a section of the boundary. The second problem concerns the indentation of a half-space by a heated rigid punch. In particular, indentation by a cylindrical punch is considered and some numerical results obtained.

Controlled Surface Flaw-Initiated Fracture in Reaction-Densified Silicon Carbide

Abstract: Controlled surface flaws were produced in commercial reaction-densified SiC by Knoop microhardness indentation. The flaws themselves could not be observed easily, thus an etching technique was used to delineate their semielliptical shape, thereby enabling calculation of the critical stress- intensity factor KIC at room temperature. Room-temperature fracture was insensitive to annealing environment (air or vacuum), flaw “healing” being observed at ≫1000°C. The variation in fracture stress of indented specimens with temperature showed 3 distinct regions of behavior which were interpreted in terms of residual stress relief, flaw healing, and Si-SiC bond weakening.

Method of forming counter sink on metallic plate

Abstract: PURPOSE:To form a counter sink without back indentation by a plastic working of metallic plate particularly thin plate.

On the Ball Indentation Hardness for Plastics

Abstract: By applying the extended Meyer's law proposed by the author to the relation among the depth of indentation h, the initial load Po, the major load Pm and the diameter of steel ball D, the following equation was obtained analytically : [numerical formula]where A and n called Meyer's index are constants for the material and Pt=Po+Pm. The relation was verified as correct experimentally. Furthermore, the effects of errors in Po, Pm and D on the hardness HK were calculated from the above relation and verified, and the total error ΣΔHK due to each permissible error of the tester can be restricted to ΣΔHKK/H≒±5 % in the worst case.

End rotation of a strip when indented by a wedge

Abstract: Experiments are described for the one-sided unconstrained indentation of half-hard and annealed aluminium strip with a wedge-shaped tool. The mechanics of the process are described and the end-rotation, which occurs after a certain critical penetration has been reached, is measured. At the present time there is no slip-line field solution which predicts this phenomenon.