Simulated Service Conditions

Here Acto is the cyclic stress range for failure in Nf cycles under zero mean stress, and Acr m is the same thing for a mean stress of a .) Goodman s Rule is empirical, and does not always work - then tests simulating service conditions must be carried out, and the results used for the final design. But preliminary designs are usually based on this rule. 

Here is the number of cycles to fracture under the stress cycle in region i, and Nj/Nf is the fraction of the lifetime used up after N, cycles in that region. Failure occurs when the sum of the fractions is unity (eqn. (15.4)). This rule, too, is an empirical one. It is widely used in design against fatigue failure but if the component is a critical one. Miner s Rule should be checked by tests simulating service conditions. 

Simulating service conditions avoids all the risks of using real service, and offers the possibility of moderate acceleration by simulating the worst conditions possible. The name implies that all factors present are considered, for example mechanical stress and the environment. However, the time scales will still be long and in many cases it is difficult, if not impossible, to simulate real conditions accurately. Clearly, simulated service trials are most attractive where the expected lifetimes are relatively modest and the conditions to be simulated are not too complicated. 

To simulate service conditions tests may be needed with exposure being on one side of the test piece only, which can achieved by using a simple jig in which the test piece forms one end of a cylindrical container. If immersion under pressure is needed a special jig would have to be developed. The standard does not include cases of partial immersion nor immersion under pressure. 

Standardised test methods for fuel cells and fuel cell systems under simulated service conditions at the JRC-IE testing facilities... 

Product performance tests under simulated service conditions. 

The second class includes tests for ageing, oxygen and ozone attack, adhesion, resistance to wear and tear, fatigue, etc. This class also includes tests under simulated service conditions under laboratory environments and immersion in fluids. These two classes of tests are conducted on vulcanized rubber. 

The exposure can be either in air or a liquid chosen to simulate service conditions. Commonly, ring test pieces are chosen for liquid exposure, so simulating the geometry of practical seals and giving a relatively large surface area to volume ratio so that equilibrium swelling is reached reasonably quickly. It should be noted that the swelling effect of the liquid will affect the relaxation pattern measured and an increase in stress may be seen over a limited time period if there is a volume increase. 

Set tests are made in either tension or compression and for their prime use, quality control, the choice of mode can be made according to the convenience of the test piece available. If intended to simulate service conditions, e.g. indentation of flooring, the most relevant mode of deformation would be used. Tests can be carried out in which the test piece is subjected to either constant stress or constant strain but, as the latter is by far the most widely used, the illustration of set measurement given in Figure 11.3 is based on constant strain in the compression mode. 

Testing Fire-Retardant Paints under Simulated Service Conditions... 

In applications where possible degrading elements exist, candidate adhesives must be tested under simulated service conditions. Standard lap shear tests, such as ASTM D1002, which use a single rate of loading and a standard laboratory environment, do not yield optimal information on the service life of the joint. Important information such as the maximum load that the adhesive joint will withstand for extended periods and the degrading effects of various chemical environments are addressed by several test methods. Table 15.2 lists common ASTM environmental tests that are often reported in the literature. 

Lack of standards in testing for refractories becomes apparent when one realizes that factors such as sample size and geometry, state of stress in the lining, thermal gradient, thermal cycling and duration are difficult to scale down to a laboratory scale to simulate service conditions. Accelerated tests involving severe conditions do not always conform to realistic conditions and may lead to unrealistic results. 

Hi) In very critical situations, test for corrosion under simulated service conditions. All these are sensible precautions, whether molybdenum disulphide is used or... 

Cutting or puncture tests are. as mentioned previously, normally made with geometries intended to simulate service conditions. 

The laboratory equipment designed to test the aforementioned tire properties is based mostly on a steel flywheel with the appropriate monitoring devices such as transducers and infrared temperature monitors. Data are collected directly into computers for real-time analysis and downloading to the tire engineer s work station. Many of these flywheels are also computer controlled so as to simulate service conditions. For example, aircraft tires can undergo a complete cycle of taxi, takeoff, and landing. 

Routschka et al. Studies on the behaviour of magnesia, spinel and forsterite refractory bricks under simulated service conditions in the middle regions of oil-fired glass furnace regenerators. Glastech. Ber. Glass Sci. Technol. 63 (1990), no.3, pp. 61-68. 

In applications where possible degrading elements are present, candidate adhesives should be tested under simulated service conditions. Common ASTM environmental test methods often reported in the literature include the following, described in Chapter 12 ... 

This test also requires special equipment and generally consists of three parts a preliminary ignition test, a fire penetration test and a spread of flame test. The specimen is subjected to radiant heat and a vacuum is applied to one side to simulate service conditions. A specified flame is applied to the test piece for various durations and the time for the flame to penetrate, as well as the maximum distance of flame spread, are noted. Glowing, flaming or dripping on the underside of the specimen are also taken into consideration. Results are classified as follows ... 

The testing is not limited to plastics resin form only. Besides the resin itself, very often testing the fabricated part in its final form needs to be an essential part of the design validation step to ensure that end-use performance requirements are adequately realized. Such part tests will have to be application specific and often need to involve testing imder actual or simulated service conditions employing specialized and nonstandard methods/procedures. 

Traditional evaluation procedures are generally laborious, time consuming, and expensive because they require fabrication of prototype parts and testing under actual end-use or simulated service conditions. These processes are more empirical than analytical, making the results of questionable value. The processes are generally impractical because they require months or years to produce results. 

Laboratory coupon (including electrochemical tests) data obtained in simulated service conditions... 

Attempts to assess sensitization in Type 304 alloy by means of 5-15 min potentiostatic electrochemical tests in solutions that simulated exactly the plant conditions have been shown to be invalid [42]. This testing period is much too short for testing in simulated service conditions, i.e., the electrode potential applied to the specimen in the laboratory test, the solution compositions, and temperature were the same as those to be used in plant service. Thus, there was no accelerating factor in the laboratory test and it would have had to be just as long as a plant test, perhaps 3-12 months, to determine whether or not the material would be subject to intergranular attack in plant service. 

The test method uses an ammonia atmosphere to simulate service conditions under which stress corrosion cracking may occur. This test method is suitable only for products fabricated from copper alloys that are known to be susceptible to stress corrosion cracking in ammonia vapor atmospheres. It is intended to create an enviromnental condition of reproducible severity, but it is well known that the critical step in the cracking mechanism is the development of an environment in the condensate film that occurs on the test specimen, which is rich in complex copper ions. 

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