Sample strain

To illustrate the effect of radial release interactions on the structure/ property relationships in shock-loaded materials, experiments were conducted on copper shock loaded using several shock-recovery designs that yielded differences in es but all having been subjected to a 10 GPa, 1 fis pulse duration, shock process [13]. Compression specimens were sectioned from these soft recovery samples to measure the reload yield behavior, and examined in the transmission electron microscope (TEM) to study the substructure evolution. The substructure and yield strength of the bulk shock-loaded copper samples were found to depend on the amount of e, in the shock-recovered sample at a constant peak pressure and pulse duration. In Fig. 6.8 the quasi-static reload yield strength of the 10 GPa shock-loaded copper is observed to increase with increasing residual sample strain. 

Figure 1.8 (left). IPF for a PTFE sample strained 1 in. (35%) at 25°C. presented in a polar equal-area projection. ( rystallographic directions are given by poles to the indicated planes. Contours represent the tendency for crystallographic directions to be aligned with the tensile axis."... 

Procedures. The specimens were tested in an Instron Universal testing machine at 0°, 23°, 50°, and 75°C and at crosshead extension rates of 0.02, 0.2, 2.0, and 10.0 inches/min. Clip-on strain gage extenso-meters were used to record sample strain, and testing was done in an environmental chamber capable of maintaining the selected temperature to within 0.5°C. All samples were soaked at temperature for at least 30 min before testing. 

The data collection system consists of a photodiode for each interferometer, an amplifier, A->D board [Metrabyte], and a personal computer for collecting the data in real time. With the exception of the sample and reference mirrors located in the reactor, all of the other components for measuring the sample strains are external to the reactor. Thus, it is not necessary to disturb the sample in order to make these in-situ sample strain measurements. 

The surface free energy of thin foils can be determined at temperatures between the melting point and approaching the Tammann temperature of the metal using the zero creep/laser interferometer technique. The use of the laser interferometer allows smaller sample strains to be measured with a higher level of confidence. 

Hg. 24. Plot of the extension ratio in the craze versus temperature for PS samples strained at a rate of... 

Cell. For solution samples, strain-free and high-quality quartz cells specially made for CD measurements are used. Cylindrical cells (cell length 100—0.1 mm), rectangular cells (cell length 20—1 mm), and U-shape cells (cell length 0.5—0.1 mm) are commercially available. 

An advanced rheometric expansion system (ARES) is used to determine Tg of samples. Strain sweep experiments from 0.01 to 1% strain are conducted to ensure that experiments are carried out in the linear viscoelastic region. All experiments are done at a frequency of IHz and a strain level of 0.05%, which is in the linear region. Temperature sweeps are conducted at a heating rate of 5°C/min over a temperature range which covers the glassy and rubbery regions of the soy flour samples at different water activities. The temperature at which the loss modulus (G") was at a maximum is used to estimate the T . 

Sample Strain, % Starting fusion °C P- a- Melting Melting point, point. Jg- Jg- Xp, % % X, % ... 

While the position and intensity of peaks in a powder pattern are determined by the unit cell size and contents, their shapes and widths are determined by instrumental effects (which can be coiTected for or modeled) and sample properties, such as the sizes and strains of crystallites and stacking faults.The simplest expression for peak broadening due to sample size (the Scherrer formula) predicts that peak width and particle size are related hy fwhm = A,/ /z cos0, where K is a shape factor (often 0.9), fivhm the peak full width at half maximum. and X the wavelength absolute numbers from this expression should be treated with caution. A sample strain leads to a peak width dependence on tanO. In more sophisticated treatments, hkl-dependent peak widths can be used to obtain information on the anisotropies of size and strain in a sample. More details on the interpretation of peak shapes are given elsewhere. ... 

Contrary to the tensile strength the elongation at rupture varies with the crystal orientation. The smallest values were observed for samples strained in the [100] direction and the largest for samples oriented in the [110] direction. The elongation at rupture increased for all orientations from almost zero for the thinnest sample to about 5% in the [100] direction and 13% for the [110] orientation. In all samples the plastic deformation was observed to strongly localize. 

Olivine single crystals were specifically studied in order to test the likelihood of an olivine a-slip/c-slip transition at high pressures. To this end, steady-state deformation experiments were done on pure forsterite single crystals using a newly-developed D-DlA apparatus coupled with X-ray synchrotron radiation, which provided an in situ determination of the applied stress (c) and the sample strain rate (e). 

Although identification of chestnut samples, strains and provenances can be done using fruits and leaves, the availability of molecular methods would be useful and essential in breeding for vigour, form and increasing nut production. These, however, require samples of purified DNA, and the presence of secondary metabolites in leaves of chestnut species requires elaborate extraction and purification methods. 

Mechanical Properties. The measurement of mechanical properties is concerned with load-deformation or stress-strain relationships. Forces may be applied as tension, shear, torsion, and compression and bending. Stress is the force divided by the cross-sectional area of the sample. Strain is the change in a physical dimension of the sample divided by the original dimension. The ratio of the stress to strain is referred to the modulus. Stress maybe applied continuously or periodically at varying rates for dilferent tests. The characteristic stress-strain curve, stress relaxation, or impact behavior is very important in determining the applications and limitations of a polsrmer. 

Figure 15.1 shows the mechanical components of the 983 DMA. The clamping mechanism for holding samples in a vertical configuration consists of two parallel arms, each with its own flexure point, an electromagnetic driver to apply stress to the sample, a linear variable differential transformer for measuring sample strain, and a thermocouple for monitoring sample temperature. A sample is clamped between the arms and the system is enclosed in a radiant heater and Dewar flask to provide precise temperature control. 

This mode is used for accurate determination of the frequency dependence of materials and prediction of end-use product performance. In the fixed frequency mode applied stress (i.e., a force per unit area that tends to deform the body, usually expressed in Pa (N/m)) forces the sample to undergo sinusoidal oscillation at a frequency and amplitude (strain), i.e., the deformation from a specified reference state, measured as the ratio of the deformation to the total value of the dimension in which the strain occurs. Strain is non-dimensional, but is frequently expressed in reference values (such as %strain) selected by the operator. Energy dissipation in the sample causes the sample strain to be out of phase with the applied stress (Figure 15.2(a)). In other words, since the sample is viscoelastic, the maximum strain does not occur at the same instant as maximum stress. This phase shift or lag, defined as phase angle (6), is measured and used with known sample geometry and driver energy to calculate the viscoelastic properties of the sample. 

Values in bold type are for sample strained 0.25% in flexure during test. To convert psi to Pascals, multiply by 6,895. 

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