Repetitive stress

In some cases the number of oxide layers can be related directly to the number of breaks in the curve and there is then no doubt that the acceleration derives from repetitive stress-induced oxide cracking. 

According to the passage, why do I la mil I c employees have a high rate of repetitive stress injury ... 

In the previous section, a full-scale girder was tested to qualify the damage. However, the main members of a superstructure seldom receive the extreme damage, except in accidents or after earthquakes. Results of the Inspection often report defects of local areas. At such parts subject to intensive repetitive stresses as floor slabs and bearings, serious damages are detected due to trafific loads in service. 

A detailed description of the flow reactor system nsed in these studies has been given earlier [16]. These earlier studies [16] on the thermal and oxidative stability of fresh jet fuel used a procedure whereby fuel was pumped once through the reactor during the experiment. In the present work, 100 mL of vegetable oil was used and recirculated through the reactor for the duration of the experiment. The reactor was allowed to run for 5 h, and then the metal strip was ranoved and analyzed. This represents a regime where the lubricant is repetitively stressed during the experiment. 

Dimensional change due to temperature fluctuations is also an important issue in designing objects when dissimilar materials are joined. For example, if the employing resin is exposed to repetitive changes of ambient temperatures, the product may crack due to repetitive stress caused by thermal expansion and contraction of the product. PPO offers the lower coefficient of linear thermal expansion than for many other thermoplastics, and minimizes dimensional change caused by temperature fluctuations. The low thermal expansion and low moisture absorption make PPO one of the most dimensionally stable thermoplastics suitable for various electronic applications. 

Actual service conditions are often characterized by a number of cycles of stress of different magnitudes. One method of assessing this failure from repetitive stresses involves the concept of cumulative damage and posits that fatigue failure will take place when the cumulative damage (the summation of incremental damages) equals unity. This is represented as ... 

Considering the repetitive stress sustained by the cylinder, the permissible stress or zui has to be the fatigue strength of the material. 

The cylinder is subjected to a repetitive stress by the hydraulic pressure. Approx. 40 strokes are performed per hour so that after an assumed life of the press of 30 years, and two 8-hour shifts per working day, and 300 working days per year, the number of load alternations = 30 X 300 X 2 X 8 X 40 = 5,760,000 is attained. Therefore, the fatigue limit has to be calculated as per Wohler s diagram. 

It has still to be mentioned that the middle part of the column with some of the pitches, which cannot be prestressed, is subjected to a full repetitive stress however, no forces are transmitted from these pitches to the nut. The fatigue-stress concentration factor existing here is therefore the considerably lower one of the notched bar. 

Stress fractures result from repetitive stress forces transferred to bone they can be divided in fatigue fractures and insufficiency fractures. Fatigue fractures occur when normal bone undergoes repetitive overuse stressing distal to the fracture site. Insufficiency fractures involve weakened bones that are more vulnerable to normal stresses these fractures are observed in aged women with osteoporosis and involve, in most cases, the calcaneus and the metatarsals. On the other hand, fatigue fractures typically involve the lower extremities... 

The Texas City explosion is but one of many examples of dramatic workplace accidents that engulfed the country during the later stages of the Laissez Faire Revival, a few of which are described in Box 8.1. In addition to the dramatic loss of life and limb that attended catastrophic accidents, the workplace extracted a less dramatic daily toll on workers who were maimed by repetitive stress injuries and poisoned by toxic dusts and chemicals as related in Box 8.2. 

Slaughterhouses. On the cutting floor of a slaughterhouse, workers slice cattle carcasses on mechanical assembly lines that move at a rate of up to 400 carcasses per hour. In addition to causing deep cuts and dismemberment, the repetitive motions can cause carpal tunnel syndrome and other repetitive stress diseases. The animal slaughtering and processing industry reported almost 27,000 lost workday injuries in 2008. ... 

Job-induced repetitive stress injuries is the fastest-growing category of workplace injuries. Specific stress factors include repetitive motion, awkward posture, heavy lifting, or a combination of these factors. According to the Bureau of Labor Statistics (BLS) lost- time injuries and illnesses reported in 1993 included the following ... 

In another part of the BLS report, organizations that insure for workers compensation estimated 2.73 million workers compensation claims for repetitive stress injuries in 1993. These injuries cost employers more than 20 billion. 

There are many individuals in the health care, insurance protection coverage, and safety professions who think that repetitive stress injuries are rising faster than any other workplace health concern. This problem is not confined to the warehouse environment. It is not unusual for a manufacturer of computer keyboards to lose a court case for injuries suffered from the use of their product. A major keyboard manufacturer lost a court case in 1996 in which a worker in New York was awarded 5.3 million. The settlement amount may be unusual, but equipment manufacturers have been the targets of numerous product liability lawsuits. 

---