Thickness of test specimens

Scale, thickness of test specimens and condition of the edges can have a pronounced effect on observed changes under accelerated testing, particularly for moisture uptake and... 

Electrode arrangement ball 20 mm, sheet 50 mm, thickness of test specimen 0.5 mm. 

Specimens are thin sheets or plates having parallel plane surfaces and are of a size sufficient to prevent flashing over. Dielectric strength varies with thickness and, therefore, specimen thickness must be reported. The dielectric strength varies inversely with the thickness of the specimen. The dielectric strength of plastics will drop sharply if holes, bubbles, or contaminants are present in the specimen being tested. 

Materials Description. Three CIBA-GEIGY epoxy/hardener systems were studied Araldite 6010/906, Araldite 6010/HY 917 and Araldite 6010/972 with stoichiometries 100/80, 100/80 and 100/27, respectively. Araldite 6010 was a DGEBA epoxy resin. The hardeners 906, HY 917 and 972 were, respectively, methyl nadic anhydride (MNA), methyltetrahydro phthalic anhydride (MTPHA) and methylene dianiline (MDA). These systems were investigated previously for the matrix controlled fracture in composites (6-8). The curing cycles used can be found in (6). The ideal chemical structures of the systems are shown in Table I. Neat resins were thoroughly degassed and cast into 1.27 cm thick plates for preparation of test specimens. 

Figure 1. Schematic diagram of test specimen Ni film of thickness, t, on PET substrate of width w strained in direction of arrows. Dotted lines represent brittle cracking. The x-coordinate is measured in the direction of strain from the edge of a film segment.

Constant-Deflection-Compression-Set Test ASTM D 3574 -Test D. This test consists in deflecting the flexible foam specimen under specified conditions of time and temperature and noting the effect on the thickness of the specimen. Ordinarily the specimen is deflected to 50%, 75%, or 90% of its thickness. The entire assembly is then placed in a mechanically convected air oven at 70°C (158°F) and 5% RH for 22 hours. Following this exposure the specimen is then removed from the apparatus and the recovered thickness measured. The constant-deflection compression set, expressed as a percentage of the original thickness, is then calculated. 

This test covers the punch-type of shear test and is intended for use in determining the shear strength of test specimens of organic plastics in the form of sheets and molded disks in thicknesses from 0.127 to 12.7 nun (0.050 to 0.500 in.). 

Naturally, leather absorbs some liquid water but mainly is water resistant. The leather industries do not claim that it is waterproof. So-called waterproof leathers are finished with water repellent agents such as organo-silicon, fluorocarbon and so on. Water absorption of leather can be tested by a static absorption method (ASTM D1815, 2000a). Cut the conditioned specimen with a circular cutter. Measure the diameter and thickness of the specimen. Calculate its volume in cubic centimetres. Weigh the specimen to the nearest 0.01 g. Immerse the specimen in distilled water at 23 1 °C in ahorizontal position with the grain side up. Leave the specimen immersed for a period of 30 min. At the end of immersion, take out the specimen and blot the surface of the specimen with filter paper to remove excess water. Weigh the specimen immediately to the nearest 0.01 g. Calculate the amount of water absorbed by the specimen ... 

For comparison of load-deflection curves, real load (P) was converted to an equivalent load (Ptq) to remove the thickness effect of tested specimens by the following equation ... 

The dielectric strength can be defined as the voltage that will produce a catastrophic decrease in the resistance of an insulator divided by the thickness of the specimen, so that it has units of volts/length. It is affected by a variety of factors, including the polymeric structure, the specimen geometry, and the testing conditions. 

For a tensile test or a compressive test, the cross-sectional area (width X thickness) of the specimen should be determined. Stress is the ratio of the load (P) to the cross-sectional area (A) ... 

There is no special requirement for specimens for weathering except that they should fit specimen holders and racks supplied with the exposure apparatus. Exposure of at least three replicate specimens of each test material and of control material is recommended. Thickness of test and control specimens should approximately be the same (within 10%). 

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