Test piece history

The test piece history is different to that of the product. 

These comments make it clear that any result is not material specific but relates to the particular sample of material, the manner in which it was processed and what has happened to since it was formed. In an ideal world the test result would be accompanied by statements covering test piece history but frequently this is not possible. 

Derham [38] has investigated many of the factors affecting test performance. Test piece history is important, especially with filled rubbers, since prestressing reduces the creep rate and there need not be a full recovery. Temperature control is also essential, since thermal cycling can significantly increase creep. 

The methods for the preparation of test pieces (or products) and their subsequent history will influence the material properties. Consequently, it is important for any testing that all the moulding, storage, preparation and conditioning procedures are defined and carefully controlled. It may be worthwhile conducting preliminary trials. 

The reciprocating paddle instrument is now largely a matter of history and a third type, the rotorless curemeter, has rapidly become the most popular. The rotorless type is a curemeter in which one half of the die enclosing the test piece, rather than a paddle or disc within the test piece, oscillates or reciprocates (Figure 6.7). 

As with pendulum force measuring systems, the use of a ruler or a piece of string to measure elongation of dumb-bells is largely history - to the relief of technicians whose fingers were frequently stung by the recoiling halves of the test piece after rupture. 

The results of dynamic tests are dependent on the test conditions test piece shape, mode of deformation, strain amplitude, strain history, frequency and temperature. ISO 4664 gives a good summary of basic factors affecting the choice of test method. Forced vibration, non-resonant tests in simple shear using a sinusoidal waveform are generally preferred for design data as... 

The standards note that the test results are dependent on the thermal history of the test pieces as well as the prevailing temperature and. for certain plastics, the relative humidity during conditioning and testing. Examples of the effect arc shown in the appendices to the standards. 

When cold urticaria is suspected by history, the diagnosis should be confirmed in two steps (1) confirmatory provocation tests and (2) clinical and laboratory examinations to rule out secondary cold urticaria. In the office, spraying of the skin with ethyl chloride can be employed as a screening test. More reliable and specific is the ice-cube test. Pieces of ice suspended in cold water are placed into a container and left on the lower arm for 3-5 min, in milder cases even for up to 10 min or even 20 min. In 76% of patients, reactions occur after 10 min and in 100% after 20 min (Neittanmaki 1985). The test is positive when a wheal or angioedema develop on re-warming of the skin. 

After DDT Better Knowledge Means. . . More Chemicals The decline and fall of DDT is a piece of environmental history well documented elsewhere. Concerns about the chemical had in fact been pronounced by military scientists who had animal tested the compound during the Second World War. This was followed by a far greater concern about the impact of the... 

In a study of allergic contact dermatitis in consumers, 1813 consecutive patients were tested with an additional textile series of 12 reactive dyes, and 18 patients (0.99%) were found to be sensitized to reactive dyes. However, only five patients had a history of intolerance to garments, and two of the four patch tests performed with pieces of garment were positive. In practice, reactive dyes in clothing should not be sensitizers. If they can be extracted from fibers, they are in a hydrolyzed, nonsensitizing form. 

When test equipment is found to be out of calibration, the validity of the tests performed since the last cahbration should be evaluated. For this purpose a history of usage should be maintained for each piece of test equipment. Test equipment found to be out of cahbration should be identified by a tag or other suitable means. 

The inspection or testing frequency has to be determined. Traditionally this has been based on manufacturer recommendations or on good engineering practice. A recent trend is to establish inspection intervals for individual types of equipment based on results of reliability analyses. Reliability data serve as necessary data inputs to such analyses. In order to establish a database on barrier reliabiUty, it is necessary to tag each piece of equipment and to record its inspection/test, repair and maintenance history. 

---