Environmental testing Acceleration test

An example of a basic environmental test bed would be a temperature controlled tank of a liquid, perhaps sea water. This basic structure is applicable to a considerable range of products and can involve acceleration by using more severe conditions than in service. In one use of such a rig, the insulation on oil riser pipes is tested by circulating hot oil through the pipe whilst it is immersed in the tank. 

Environmental and accelerated ageing tests were performed on the indoor dye modules described in Sect. 7.6 in order to detect failure mechanisms. Contrary to expectations, many modules survived humidity/freeze cycling tests (10 cycles, 85%, 20 h at 55°C per cycle) without major degradation, demonstrating the capability of the sealing concept (see Fig. 7.8). This was also true for temperature cycling (between —5 and 55°C). However, it has... 

Environmental Tests. It is desirable to know the rate at which an adhesive bond will lose strength due to environmental factors in service. Strength values determined by short-term tests do not give an adequate indication of an adhesive s performance during continuous environmental exposure. Laboratory-controlled aging tests seldom last longer than a few thousand hours. To predict the permanence of an adhesive over a 20-year product life requires accelerated test procedures and extrapolation of data. Such extrapolations are extremely risky because the causes of adhesive bond deterioration are complex (see Sec. 15.2.2). Unfortunately no universal method has yet been established to estimate bond life accurately from short-term aging data. 

It has good self-adhesion, as well as adhesion to ceramic and metal. The polymer performs satisfactorily in accelerated environmental tests. The polymer and its properties will be discussed in this paper. 

Although cyclic environmental chamber test procedures may suffice for failure processes Involving, for example, mechanical stress, kinetic controlled processes dependent upon time and temperature such as oxidation and diffusion do not lend themselves to adequate Identification and analysis based solely on number of cycles. Thus Sandia National Laboratories developed an accelerated aging protocol for environmental testing which (1) identifies material incompatibilities and subsequent failure modes in Phase I and (2) proceeds with kinetic analysis of the Arrhenius type of failure mode processes which allow extrapolation necessary for lifetime prediction of components in Phase II. Thus two phases are necessary in a complete analysis to accurately predict system lifetimes. The accelerated aging protocol requires the Identification of the stresses that are most likely to damage the performance of the component under test. However, data is frequently not available on the performance of a system under a particular stress. When this is the case, it becomes necessary to make predictions of those stresses most likely to cause degradation and then test to see if the stresses selected are dominant. 

Many environmental tests are accelerated because if they were not they would offer no advantage over a field trial. This introduces the problem seen with heat aging tests of satisfactorily extrapolating from short-term tests to long-term service conditions. When several environmental factors are present simultaneously, this difficulty is greatly increased. Extrapolation of accelerated environmental resistance data is discussed in Chapter 29. 

Accelerated environmental testing should only be nsed when there is sufficient correlation with testing under tme environmental conditions for an accurate evaluation of the test results to be made. 

MIL-STD-810E-14 July 1993-Environmental Test Methods and Engineering Guidelines—Pressure, temperature, temperature shock, solar radiation, rain, humidity, fungus, salt fog, sand and dust, explosive atmospheres, acceleration. 

Environmental testing— Part 2 Tests— Test Cy Damp heat, steady state, accelerated test primarily in-... 

Environmental test rooms Environmental test rooms which permit various combinations of temperature, fogging, humidity levels, and shower effects to simulate rain can reproduce in an accelerated mode many of the factors present in an actual exposure. For the most part, these tests use small cut or machined specimens, but assemblies of simulated components and complete systems can also be tested as shown in Fig. 11.35. 

However, other approaches have also successfully been adopted. For example, Dickie and Ward [53] have studied single-lap joints exposed to a high humidity at moderately elevated temperatures but maintained a constant stress on the joints. Also, periodically the joints were removed from the high-humidity environment and exposed to a salt solution for a short time period. Using this accelerated-ageing test they were able to rank the durability performance of various adhesive systems in a comparatively short timescale. Further, they reported that not only were the kinetics of mechanisms of environmental attack accelerated, but also the exact details of the mechanisms were affected by the levels of the applied load. For example, for joints which consisted of bonded galvanised steel substrates, the effect of relatively high applied loads was to prevent the formation of an effective barrier of corrosion products, i.e. passivation of the substrate surface was prevented. This allowed the electrochemical corrosion process to proceed unimpeded, and hence at a faster rate than for similar, but unstressed, joints. Thus,... 

Short-term tests do not always give an adequate indication of an adhesive s performance during end user applications. Laboratory tests may only be carried out over a thousand hours, and the joint may only be exposed to one type of environmental effect at a time. During its service life, however, the bond is exposed to multiple types of environments. Temperature and humidity may cause an adhesive bond to degrade much faster than when exposed to any single environment. Applied stress accelerates the effect of the environment on an adhesive joint. Data are not always readily available from manufacturers on this phenomenon. Environmental testing should be carried out on the proposed adhesive and adherend prior to its use in service. 

To complete the selection trials applied to the conductive adhesives, MIL-STD-883 has issued a series of sequential environmental tests mainly aimed at devices used in the aerospace industry. The three tests are humidity-induced stress tests at elevated temperatures with and without bias, temperature-induced stress tests with and without bias, and a mechanical shock comprising acceleration 3000, 0.3 ms and constant acceleration 15,000 g (MIL-STD-883, Method 2001). The most severe tests are those involving both humidity and temperature, because they... 

All testing has to be related to environmental conditions whose characteristics must be defined. The relation of accelerated corrosion test condition to real service conditions is one aspect while another is defining classes of environment and relating them to characteristic corrosion performance in order to produce useful specification guidelines. BS5493 1977 is an attempt to do this using four categories appropriate primarily to the UK (Table 13.2). Such a classification is clearly an over-simplification, but represents an important step in this particular direction. 

Environmental Cracking The problem of environmental cracking of metals and their alloys is very important. Of all the failure mechanism tests, the test for stress corrosion cracking (SCC) is the most illusive. Stress corrosion is the acceleration of the rate of corrosion damage by static stress. SCC, the limiting case, is the spontaneous cracking that may result from combined effects of stress and corrosion. It is important to differentiate clearly between stress corrosion cracking and stress accelerated corrosion. Stress corro-... 

M. Regert, S. Colinart, L. Degrand, O. Decavallas, Chemical alteration and use of beeswax through time accelerated ageing tests and analysis of archaeological samples from various environmental contexts, Archaeometry, 43, 549 569 (2001). 

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