Engineering Strain Rate Research Articles

Stress-Strain Equations for Some Near-Eutectic Tin-Lead Solders

This paper presents the evaluation of the stress-strain behavior, as a function of strain-rate, for three tin-lead solders at room temperature. This behavior is critically needed for reliability analysis of printed circuit boards (PCB) since handbooks list minimal mechanical properties for the eutectic solder used in PCBs. Furthermore, most handbook data are for stable eutectic microstructure whereas PCB solder has a metastable microstructure. All three materials were purchased as “eutectics.” However, chemical analysis, volume fraction determination, and microhardness tests show some major variations between the three materials. Two of the materials have a eutectic composition, and one does not. The true stress-strain equations of one eutectic and the one noneutectic material are determined from compressive tests at engineering strain-rates between 0.0002/s and 0.2/s. The second eutectic material is evaluated using tensile tests with strain-rates between 0.00017/s and 0.042/s. The materials appear to exhibit linear elastic behavior only at extremely small strains, i.e., less than 0.0005. However, this “elastic” behavior showed considerable variation, and depended upon the strain rate. In both tension and compression the eutectic alloy exhibits nonlinear plastic behavior, i.e., strain-softening followed by strain-hardening, which depends upon the strain rate. A quadratic equation σy = σy(ε˚/ε˚0) + A(ε˚/ε˚0)ε + B(ε˚/ε˚0)ε2 fit to the data gives correlation coefficients R2 > 0.91. The coefficients σy(ε˚/ε˚0), A(ε˚/ε˚0), B(ε˚/ε˚0) are fitted functions of the normalized engineering strain rate ε˚/ε˚0. Replicated experiments are used at each strain-rate so that a measure of the statistical variation could be estimated. Measures of error associated with the regression analysis are also obtained so that an estimate of the total error in the stress-strain relations can be made.

Intergranular Fracture of Lithium Fluoride–22% Calcium Fluoride Hypereutectic Salt at 800 K

Constant‐velocity compression tests were conducted at 800 K on as‐cast LiF‐22 mol% CaF2 hypereutectic salt with engineering strain rates varying between 1.8 × 10−6 and 2.3 × 10−1 s−1. Considerable stain hardening was observed during the initial stages of deformation, and the true stress‐strain curves exhibited maxima. Plots of the true strain rate against the flow stress at the proportional limit and the peak stress exhibited a power‐law relation with stress exponents of 7.7. Microstructural examination of the deformed specimens showed extensive grain‐boundary cracking and cavitation. These results suggest that grain‐boundary cracking and interfacial sliding is important for cavity nucleation at the grain boundaries and at the LiF‐CaF2 interfaces, and cavity growth and interlinkage, which appear to depend on the morphological differences between different grain boundaries, occur through the preferential failure of the weaker LiF phase.

Hydrostatic extrusion of amorphous polymers and properties of extrudates

Abstract Poly(methyl methacrylate) (PMMA), high-impact polystyrene (HIPS), polycarbonate (PC), poly(vinyl chloride) (PVC), and acrilonit rile-butadiene-styrene copolymer (ABS) were hydro-statically extruded with various extrusion ratios up to 3. The temperature of extrusion ranged from room temperature to 100°C. The rate of extrusion was varied between 0.90 and 2.8 sec−1 in terms of engineering strain rate at the die exit. Round and sheet billets were employed, and some of the round billets were gridded on their meridian section for visioplasticity study. An approximately linear relationship was obtained between the observed extrusion pressure and extrusion ratio. The visioplasticity study revealed that the billets were subjected to almost uniform deformation during the extrusion process. A modified von Mises' yield criterion was employed to obtain an extrusion pressure vs. extrusion ratio relation which was in good agreement with the observed data. The extrudates were subjected to tensile, bend, torsion,...

Influence of chromium on superplasticity in ultra-high carbon steels

The influence of chromium additions to ultra-high carbon steels has been investigated. A common bearing steel (52100 containing 1% C and 1.5% Cr), a 1.6%+1.5% Cr steel (designated 52160) and a plain 1.6% C steel have been compared. Chromium is found to enhance greatly the superplastic properties. This is because the chromium enters the cementite and thereby stabilizes it. This in turn allows very little grain growth in ferrite to occur during superplastic deformation. A value of 1220% elongation to failure in 52160 was found at 650° C at an initial engineering strain rate of 1% min−1. The influence of strain rate on the elongation to failure has also been investigated in this material.

Longitudinal tensile properties of H4LM graphite in the temperature range—253 to 500°C

Tensile strength data are presented for a molded H4LM graphite tested in the longitudinal orientation (“across the grain”) at a nominal engineering strain rate of 0·0005/min in liquid hydrogen at −253°C, in liquid nitrogen at −196°C, and in air at room temperature, 250 and 500°C. All ultimate strength values at all of these temperatures fall within the scattering of room-temperature strength measurements.

Effects of temperature and strain rate on transverse tensile properties of H4LM graphite tested in helium and in vacuum

Curves are presented showing the ultimate tensile strength of molded H4LM graphite in the transverse orientation (“with the grain”) as a function of temperature, for tests made in vacuum and in static helium at nominal engineering strain rates of 0.005, 0.5 and 2.0/min. Temperature ranges considered are ambient to 2000°C for tests in vacuum, and ambient to 2500°C for those in helium. A general increase in strength occurs as temperature rises; however, the magnitude of the strength increase is reduced by testing at the higher strain rates. Fracturing of graphite is discussed, and it is concluded that these results can best be explained in terms of a selective mass-transport mechanism which heals, or at least blunts, dormant cracks formed early in the fracture history.

Longitudinal tensile behavior of h4lm graphite in nitrogen to 2750 °C

Data are presented on the ultimate tensile strength, 0,2% yield strength, and permanent elongation of a molded H4LM graphite tested in the longitudinal orientation (“across the grain”) in static nitrogen, at a nominal engineering strain rate of 0.005/min, at temperatures from ambient to 2750°C. Under these conditions ultimate strength increases quite regularly with temperature to a maximum near 2500°, where it is almost three times the room-temperature value, then falls off sharply. Yield strength coincides with ultimate strength to about 2400°, then decreases rapidly with higher temperature. Permanent elongation in advance of fracture remains very small to above 2375°, is about 1 % at 2500°, and increases to about 10% at 2750°. A change in fracture behavior is noted at about 2500°C, which correlates with the observed elongation increase, and may explain the reversal in slope of the strength vs. temperature curve.