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Internal stresses developed during deformation are defined and its measurement described. Its applications in work hardening and the ductility of polymers are illustrated. The internal stress developed under an indenter is shown to agree with the results from conventional tests. The development of internal stress under an indenter can be used to determine deformation mechanisms.

The heat transfer problem of a moving heat source along the surface of a half space was studied analytically and numerically. For the 2D problem, the heat source was a strip moving source and for the 3D problem, the heat source was a square moving source. Analytical solutions are available only for adiabatic conditions as given by Carslaw and Jaeger [H.S. Carslaw, J.C. Jaeger, Conduction of Heat in Solid, second ed.,Clarendon Press, Oxford, 1959, pp. 269–270; H.S. Carslaw, J.C. Jaeger, Conduction of Heat in Solid, second ed., Clarendon Press, Oxford, 1959; J.C. Jaeger, J. Proc. R. Soc. N. S. W. 76 (1943) 203–224]. With convection cooling over the surface of the half space, finite element method was used to simulate the transient heat transfer process. It was found that, for the same heat source, the shape of temperature contour over the contact interface was not sensitive to the convection coefficient of the environment. If the heat source emits the same amount of heat per unit distance of travel, both the maximum and the average temperature of the interface increase with the speed of motion of the heat source. On the other hand, the thermal layer thickness defined as the depth at which the temperature is one half of the maximum temperature at the interface decreases with increasing speed of motion of the heat source. For a brass-bonded diamond tool sliding over a glass substrate, the FEA simulation results showed that 2.2% of the friction heat entered the glass substrate for water cooling and 3.4% for air cooling. User subroutine DFLUX was written to simulate the moving heat source in using ABAQUS to solve transient heat transfer problems.

Spontaneous whisker growth on beta-Sn is a creep phenomenon near a surface, driven by compressive force. The compressive force is self-generated and the sample responses by growing stress-free whiskers. While a whisker grows out of a surface, it requires an oxidized surface and the oxide has to be protective. An oxide-free metal under compression in ultra-high vacuum will not grow whiskers. Due to a very limited temperature range, from room temperature to 60 °C, of spontaneous growth of Sn whiskers, a systematic study of the growth is difficult because if the temperature is lower, there is insufficient atomic diffusion and if the temperature is higher, there is no driving force because of stress relief. In this paper we review briefly the creep behavior of whisker growth on beta-Sn surfaces. We present a model of grain boundary fluid flow mechanism of growth of Sn whiskers. The agreement with experimental observation is discussed.

The creep behavior of a precipitation hardenable Mg-8Zn-4Al-0.5Ca (wt.%) casting alloy was determined by using impression creep tests in the temperature range of 403–623 K and under the punching stress range of 1.68–60.4 MPa. Using a power law between the steady-state impression velocity and the punching stress, it was found that the stress exponent changes with both stress and temperature. The activation energy evaluated at the same punching stress was found to be a function of the punching stress and changed from 76.5 kJ/mol at 13.4 MPa to 45.4 kJ/mol at 46.95 MPa. However, by using a hyperbolic sine stress law between the steady-state impression velocity and the punching stress, a single activation energy was found to be 77.5 kJ/mol, which is about half of the activation energy for lattice diffusion in Mg. A single mechanism of grain boundary fluid flow was proposed to be the controlling mechanism for the creep behavior of the Mg-8Zn-4Al-0.5Ca alloy under the testing conditions.

The adiabatic reaction temperature of stoichiometric Ni+Al and 3Ni+Al elemental mixtures and non-stoichiometric Ni/Al reaction systems under various initial conditions are calculated and compared with experiments. The experiments are based on the measurement of temperature–time profiles of the combustion reactions carried out in a nearly adiabatic condition. The adiabatic reaction temperature changes with the fraction of Ni with a maximum at about equal atomic ratio. The experimental results are in good agreement with the calculations.

The slip process of the stick–slip phenomena during scratching of a styrene–acrylonitrile copolymer was studied. It was found that during slip the indenter velocity starts from zero, increases to a maximum and then decreases to zero again. The scratch groove made during slip showed a non-uniform depth which increased with the decrease of scratch velocity. Although the scratch velocity and groove depth changed markedly during slip, the scratch force remained almost constant for most of the scratch distance. The effects of the normal load and driving speed on the slip behavior showed that the normal load mainly determined scratch force. The results are discussed in terms of a micromechanical model proposed to describe the slip process.

Based on precise temperature measurements during combustion and microstructural analysis of quenched samples, the evolution of reaction of the NiAl combustion synthesis has been studied. The combustion reaction of a multilayer Ni/Al system takes place in a thermal explosion mode under near adiabatic conditions. The experimental results clearly show that the combustion reaction starts right after the melting of Al. From the start to completion, the reaction goes through three stages. In the first stage, the temperature rises from the melting point of aluminum to the decomposition temperature of the intermediate phase NiAl 3 , i.e. 854 °C. The reaction is the dissolution of nickel in liquid aluminum, with the formation of small amounts of intermediate phases NiAl 3 and Ni 2 Al 3 at the solid–liquid interface. In the second stage, the temperature of the system increases from 854 to about 1300 °C. The reaction is still the dissolution of nickel in liquid aluminum solution. However, due to supersaturation, solid NiAl precipitates out at about 1300 °C, generates a great deal of heat and increases the temperature suddenly. The third stage starts at about 1300 °C, and ends at the maximum reaction temperature. The reaction rate of this stage is much higher (two orders higher) than that of first and second stages. The final product, liquid NiAl, forms at this stage.

Impression creep and impression fatigue, both using cylindrical indenters, are reviewed in this paper. For impression creep, analytical solutions and computer simulations for different situations are presented. Materials tested include metals and alloys, superplastic materials, weldments, glasses, ceramics and polymers. Viscosity measurements using indentation techniques and impression creep of thin films are discussed also. For impression fatigue, a steady state per cycle is shown and the power law dependence of maximum stress is presented. Underloading and overloading effects, as well as delayed retardation, are described. Other localized tests, such as nanoindentation, stress relaxation, impression recovery and the adhesion energy determined by impression testing, are briefly discussed also.

Adhesive Hertzian contact between a solid sphere and a soft polymer medium is analyzed by using the Moutier theorem and then compared with finite element computation. The latter is then extended to polymer coatings on a rigid substrate. Scratch experiments of a spherical sapphire indenter on a polymer coating are performed and the results understood based on the above analysis.

The electric charges on the edge dislocations in KCl single crystals doped with divalent cation impurities were determined as a function of impurity concentration and temperature. This is then used to determine the density of mobile dislocations in compression, strain rate cycling, stress relaxation, latent hardening and the Bauschinger effect by using the plasto-electric effect. Some other plasto-electric, electro-plastic and magneto-plastic effects are also discussed.

Thermodynamic and thermokinetic stability conditions are used to examine micromechanical deformation. Examples in serrated yielding, buckling, stick/slip in scratching and slow/fast in slitting are examined. Other instabilities such as negative diffusivity in spinodal decomposition and negative creep in amorphous metals are discussed.

Four alloying elements Zr, Hf, B and C added in intermetallic NiAl were found to enhance yield strength. The large increment of yield strength observed cannot be explained by conventional mechanisms such as particle strengthening and solid solution hardening. A new approach based on break away of edge dislocations from Cottrell atmosphere is proposed. The Cottrell atmosphere, as originally proposed for interstitial atoms in the neighborhood of the edge dislocation, is extended for both substitutional and interstitial solutes, with Zr and Hf being substitutional atoms replacing Al and B and C interstitials. This quantitative model yields results in good agreement with the experimental data for the substitutional impurities, but for interstitial solutes the calculated values are smaller than the observed increase in yield stress. The embrittlement of NiAl by these solutes is also discussed in terms of dislocation pinning and the increase of yield stress.

Ni/Al (3/1) multilayer reaction piles were heated in a vacuum furnace and the temperature (100 readings per s for a precision of 0.2°C) of the reaction pile was measured continuously during the combustion reaction. The ignition temperature (at which the combustion starts) is almost the same independent of heating rate and the thickness of the foils. This temperature corresponds to the melting of Al which triggers the reaction. For thin Ni foils, less than 25 μm thick, the maximum temperature shows a plateau with time, close to the adiabatic reaction temperature or the eutectic temperature close to Ni3Al. For thicker Ni foils, the maximum temperature decreases with the increase of foil thickness and the combustion is incomplete. The reaction time between the ignition temperature and the maximum temperature (or the beginning of the plateau temperature) increases from 8 s for a 12.5 μm Ni foil to 125 s for a 150 μm Ni foil and the relation is almost linear. For Ni foils less than 25 μm thick, the final microstructure is homogeneous with a grain size approximately equal to the combined initial Ni and Al foil thicknesses. In the range used, 1–100°C min−1, the heating rate has very little effect on the combustion reaction. From the temperature-time profile and microstructure analysis, there are evidences of melting of Al, decomposition of Al3Ni and Al3Ni2, and the formation of NiAl and Ni3Al.

The effect of a surface cavity on the diffusional creep of a half space by impression of a punch whose end fits the cavity was studied analytically and numerically and compared with the normal case of the same punch of a flat end pushed into a flat surface without the cavity. A straight punch with a half cylindrical tip pushed into a half cylindrical groove of the same size as the tip produces the same impression velocity as the normal case. However, for a cylindrical punch with a semi-spherical tip pushed into a semi-spherical hole of the same size as the tip, the impression velocity is 4/π faster than the normal case. By using the finite element method (ABAQUS program), a cylindrical punch with a flat end pushed into a cylindrical cavity of the same size as the punch was also studied. If the depth of the cavity is 1.5 times the punch radius, the impression velocity is only about 5% smaller than the normal case provided that the lateral contact area is a free surface. If the lateral contact area is impermeable to vacancies, the impression velocity is about 28% smaller.

Impression creep and stress relaxation experiments on the SnPb eutectic alloy were carried out in the RSA II instrument modified to use a 0.5 mm diameter cylindrical punch under 1.5–47 MPa punching stress and within a temperature range of 25 °C to 110 °C. Based on a power law between the impression velocity and stress or between the stress rate and stress, the exponent increased with stress from 1 to 3.5 within the temperature range 80–110 °C and 2.5 to 6 within the range 25–65 °C. These exponents were generally comparable to those reported in the literature. Because of the change of stress exponent, several mechanisms have been proposed. However, the stress dependence was found to obey a hyperbolic sine function of stress for all the stresses and temperatures studied. Similarly before using the hyperbolic sine function, the activation energy was found to increase with stress, an abnormal behaviour. Fortunately, after using the hyperbolic sine function, a single activation energy, 55 kJ mol−1 was obtained. Based on the present data, a single mechanism of interfacial viscous shearing between the two eutectic phases is proposed for both creep and stress relaxation. In addition to the effect of stress and temperature, the impression velocity based on this model should be directly proportional to the punch radius and inversely proportional to the nth (n = 1–3) power of the size of phase particles. These predictions are consistent with available information in the literature.

Impression creep of materials obeying the Eyring hyperbolic sine constitutive equation is simulated by finite element analysis using the ABAQUS program. It turns out that the impression velocity is also a hyperbolic sine function of the punching stress (the applied load divided by the contact area) and if the punching stress is divided by 3.5 to change to the tension/compression flow stress, the activation shear strain volume calculated from the impression test is the same as that obtained from the tension test. For the same punching stress, the impression velocity is proportional to the punch radius, which is also found in the computer simulation using the power law constitutive equation and by dimensional analysis for both constitutive equations. The present results support the analysis of experimental data of SnPb eutectic alloys reported previously.

A straight specimen of amorphous Fe 78 B 13 Si 9 ribbon was heated by passing an a.c. current through the specimen. In addition to the Joule effect, the current-induced magnetic field was combined with a high d.c. applied magnetic field along the longitudinal direction of the specimen to improve the magnetic properties. Under the applied testing magnetic field H a = 2 Oe, the magnetic induction B m ≅14.5 kG for the heat-treated specimen is much better than the magnetic induction B m ≅8.7 kG for the as-cast specimen. The remanence ratio of the heat-treated specimen ranges from B r / B m = 0.55 at f = 20 Hz to B r / B m = 0.89 at f = 20 kHz, while the remanence ratio of the as-cast specimen is from B r / B m = 0.23 at f = 20 Hz to B r / B m = 0.46 at f = 20 kHz . This shows that the heat-treated specimen has the desired squareness of the B - H loop for some applications at high frequencies.

When dislocations of both signs are emitted from a propagating fatigue crack under mode II or mode III loading, the crack growth is much less than in the case in which dislocations of only one sign are emitted. The crack advances only during the period in which the total number of dislocations in the plastic zone is increasing. The crack growth per cycle increases with increasing applied stress ratio (the ratio of the minimum to the maximum applied stress intensity factors). Accelerated crack growth begins at a ΔK a (the difference between the maximum and the minimum applied stress intensity factors) at which the total number of dislocations abruptly changes from increasing with increasing ΔK a to decreasing with increasing ΔK a .

Dislocations with identical Burgers vectors emitted from a propagating fatigue crack for mode II or mode III loading are shown to affect the fatigue crack growth per cycle. The crack extends only during the unloading part of the cycle. The rate of growth increases with increasing ΔK = K max − K min and with decreasing stress ratio K min / K max . The cyclic variations of the local stress intensity factor, the number dislocations in the plastic zone and the plastic zone size are reported also.

The stress field around the tip of a semi-infinite crack with an edge dislocation parallel to the tip but located in any nearby position has been obtained in closed form. Using this, the equilibrium positions under mode I loading of an array of edge dislocations emitted from the crack tip on a slip plane oriented at an angle to the crack plane were obtained numerically. A dislocation-free zone (DFZ) was found to exist if the slip plane was not saturated with dislocations. The DFZ disappeared at saturation. The case of two arrays emitted on two symmetrically oriented slip planes was studied also. The effects of the applied stress, the angle of inclination of the slip plane, the lattice friction for dislocation motion and the number of dislocations in the plastic zone are presented.