Aging failure mechanisms

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... 

Thiel, B.L., and Donald, A.M. (2000). Microstructural failure mechanism in cooked and aged earrots. J. Texture Stud 31,437 55. 

In order to understand the aging or failure mechanisms of the IL electrolyte-based EDLCs, the electrochanical decomposition of the ILs in EDLCs beyond the ESPW has been investigated [35,102,103]. Using in situ infrared and electrochemical spectroscopy methods, Romaim et al. [102] reported that for [EMIM][BF4] IL electrolyte, imidazolium cation dimerized and led to the formation of l,5-diethyl-4,8-dimethyl-l,4,5,8-tetraazaf-ulvalene at the electrode potential below -2 V (vs. Ag/AgCl wire in the same IL), while the formation of BF3 complexes with BF4 anion and fluorination of the cations occurred... 

Researchers admit that the Arrhenius equation is applicable to any temperature if similar failure mechanisms occur. In the graphical representation we have placed two temperatures and the lifetimes corresponding to these temperatures. If the two temperatures are selected as usually operating temperatnre Tf, respective as accelerated aging Ta, then the two times will represent the real hfetime tf) and that of accelerated aging ta) imder conditions that simulate the usually operation. 

Based on hypothesis H confirmation the researchers on semiconductor field are interested in knowing the activation energy. The second phase of the aging research consists in determining the activation energy characteristic to the evidenced failure mechanism for this type of semiconductor device. 

The purpose of accelerated ageing is clearly to cause deterioration to the bonding system under investigation, that is, the adhesive-primer-pre-treatment-substrate combination. It is of critical importance that the ageing conditions should be selected to recreate the same failure mechanisms as wonld be seen in service conditions. 

If the ageing process mechanism does not change over the considered temperature interval, the time-to-failure versus temperature function is governed essentially by the speed of ageing k. The function is normally a simple Arrhenius law dependency ... 

Radiation failures are principally caused by uranium and thorium contaminants and secondary cosmic rays. Radiation can cause wearout, aging, embrittlement of materials, or overstress soft errors in such electronic hardware as logic chips. Chemical failures occur in adverse chemical environments that result in corrosion, oxidation, or ionic surface dendritic growth. There may also be interactions between different types of stresses. For example, metal migration maybe accelerated in the presence of chemical contaminants and composition gradients and a thermal load can accelerate the failure mechanism due to a thermal expansion mismatch. 

Li, ]. and Dasgupta, A. 1994. Failure mechanism models for material aging due to interdiffusion. IEEE Trans, on Reliability 43(1) 2-10. 

Visualisation of failure sites induced by ageing and mechanical stress... 

Becanse it is not possible to evenly accelerate all aging factors, the best testing tries to imitate an expected failure mechanism. Each test accentuates one or a few stresses that are rate-controlhng for a mechanism. By choosing the right test, it is possible to thus probe for certain expected weaknesses in the coating/substrate system. The trick, of course, is to correctly estimate the failure mechanism for a particular application, and thus pick the most suitable test. 

Changes in both the adhesion values obtained in before-and-after testing and in the failure loci can reveal quite a bit about aging and failure mechanisms. Changes in barrier properties, measured by electrochemical impedance spectroscopy (EIS), are important because the ability to hinder transport of electrolyte in solution is one of the more important corrosion-protection mechanisms of the coating. 

In the stress part of a qualification test the components are subjected to extreme environmental conditions over a longer period of time, to check v ether these conditions lead to parameter drift, aging and failures of components with time. EV the extreme environmental conditions aging phenomena are accelerated so that drifts and failures occur after a reasonably short time. However, it is inportant that no failure mechanisms are... 

Failure of rubber parts used in domestic water applications has been frequently reported, and complaints include swelling and cracking and are related to nitrile and ethylene-propylene copolymer-type compounds. An ageing test method is developed, and effects of the different chemicals used in the purification processes on nitrile and EPDM vulcanisates compared. Butyl, halobutyls, ethylene-propylene copolymers and nitrile vulcanisates are evaluated two failure mechanisms are proposed and investigated. 7 refs. 

These cyclic mechanical stresses lead to fatigue or ageing of the concerned materials. Crack formation or wear-out is a typical failure mode that can be observed. These failure modes are common if mechanical components are considered. This does not surprise as the principle failure mechanism is purely on the material mechanical side. 

The failure mechanisms of plastics under media influence can be classified into two groups analogous to the aging processes ... 

Obviously, the purpose of an accelerated ageing test is to cause a more rapid deterioration of the bonded assembly, and by paying due consideration to the actual service conditions, the accelerated ageing conditions can be selected to recreate as closely as possible the failure mechanisms that would be seen in those actual service conditions. The accelerated ageing conditions usually selected involve some environmental factors, which the bonded assembly might encounter, such as elevated temperature, UV radiation, high humidity, water... 

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