Fatigue environmental factors

General description. In incomplete fusion, complete melting and fusion between the base metal and the weld metal or between individual weld beads does not occur (Fig. 15.8). Incomplete fusion that produces crevices or notches at surfaces can combine with environmental factors to induce corrosion fatigue (Chap. 10), stress-corrosion cracking (Chap. 9), or crevice corrosion (Chap. 2). See Fig. 15.9. 

Environments. Among the environmental factors that can shorten life under thermal fatigue conditions are surface decarburization, oxidation, and carburization. The last can be detrimental because it is likely to reduce both hot strength and ductility at the same time. The usual failure mechanism of heat-resistant alloy fixtures in carburizing furnaces is by thermal fatigue damage, evidenced by a prominent network of deep cracks. 

In addition, the use of field fortification samples measures the carefulness factor of the Field Scientist during the field research and allows a Study Director/Manager or distant observer to obtain a quality control estimate on the field portion of the study. For this reason, the field fortification samples are usually meant to be different from laboratory procedural fortifications and are meant to be prepared under field conditions, which are considerably more rigorous than are controlled laboratory conditions. For example, environmental factors such as heat, humidity, wind, human stress, and other human factors such as fatigue to the Field Scientist are an integral part of any field worker exposure/re-entry study. Field fortifications made to matrices under these conditions will test and readily demonstrate the ability of the Field Scientist to perform such a difficult study under trying circumstances. 

Cold sores are caused by the herpes simplex virus serotype 1 (HSV-1). A person may become infected by transmission from another individual who has a cold sore, for example, by kissing. The vims passes through the skin and travels up the nerve, where it usually lies dormant until triggered. Common risk factors include emotional stresses, fatigue, colds and viruses that may weaken the body s immune system, menstruation and environmental factors such as cold weather and strong winds. 

Wear is the process of physical loss of material. In sliding contacts this can arise from a number of processes in order of relative importance they are adhesion, abrasion, corrosion and contact fatigue. Wear occurs because of local mechanical failure of highly stressed interfacial zones and the mode of failure is influenced by environmental factors. 

Overload. This is concerned with an imbalance between the capacity of a person at any time and the load he/she is carrying in a specified state. The capacity of a person is the product of factors such as stress, fatigue, natural ability, state of mind, degree of training, and physical condition. The load carried by a person is composed of tasks for which he/she has responsibility along with additional burdens resulting from environmental factors (e.g., distractions, noise), internal factors (e.g., personal problems, worry, emotional stress), and situational factors (e.g., imclear instructions, level of risk). 

Others lose their concentration due to job or task interruption. Healthcare workers and professionals should deal with stress, lack of sleep, and fatigue on the job. Workplace environmental factors, personal or home distractions, and substance abuse can also impair performance. James Reason in his studies developed some questions to address errors committed on the job. Consider the following questions when investigating an error or other adverse event ... 

Environmental factors affecting fatigue. Environmental attack can rapidly reduce the material s fatigue strength. This could happen in two ways ... 

The data mentioned previously in Table 13.4 give short-term mechanical properties under very simple loading conditions. These values are typical of commercially available PSF, PES, and PPSF of practical molecular weight. When one is considering a polymer for a particular end-use apphcation, it is very important to also consider other service life factors such as creep and fatigue properties as well as temperature and other environmental factors. 

All of the above limitations have been described in isolation from the effects of the external environment. General environmental conditions such as noise, glare and lighting level, dust and fumes, social environment, etc. will influence the factors which have been described above. For example, noise and high temperature both have an effect on the arousal level. Noise increases it, heat decreases it, and both have an effect on the accuracy of detection of information and the speed of processing it. These physical environmental factors are dealt with in the chapters on Occupational Health and Hygiene. The effects of fatigue and the social environment upon individual behaviour are dealt with here. 

To account for the material evolutions, guidelines dedicated to the external or internal reinforcements of concrete structures using FRP composites usually introduce substantial durability parameters (reduction factors on FRP tensile properties and on shear characteristics of FRP/concrete bonded interfaces, creep stress levels and fatigue limits) see, for instance, ACI 440.2R-08 (2008) and ACI 440.1R-06 (2006). However, further research is still needed to refine the design codes and better calibrate the durability reduction factors taking into account synergistic effects between various environmental factors. 

Durability test methods lack standardization and are not always representative of realistic service conditions it is therefore essential to develop standard accelerated ageing tests that correspond to actual in-situ environments. In particular, significant effort should be undertaken to study the synergistic effects between environmental factors (moisture, temperature, alkalinity, chemical attacks) and mechanical loads (sustained loads, fatigue) at both the material and structural scales. 

The fact that the response of polymer based materials is time dependent and/or viscoelastic has been mentioned in previous sections. Further, it has been indicated that this time dependence is inherent to polymeric materials due to their unique molecular structure and is quite different from time dependence induced in other materials such as metals by fatigue, moisture, corrosion or other environmental factors. In fact, these same environmental factors also affect polymers but manifest themselves differently than in other materials due to the intrinsic viscoelastic nature of the molecular structure. 

Of course, environmental factors as well as fatigue do influence mechanical properties as a function of time but this degradation of properties due to accumulated damage is quite separate from the inherent time dependence of viscoelasticity considered here. 

Limited short-term memory Running late or being in a hurry Inability to multitask Interruption of the job or task Stress or lack of sleep Fatigue or effects of shift work Environmental factors Personal or home distractions Drug and substance abuse... 

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