The figure below shows a sling connected to two cantilever 2

The figure below shows a sling connected to two cantilever 250 Parallel Face Channel (PFC) welded on its 250mm wide face to rigid supports. The 250 PFC material has a yield strength of 250MPa. Space constraints restrict the joint area to extend only 150 mm in from the vertical surface of the rigid support, as shown in the figure (note the figure is not to scale). For a factor of safety of 2.5 and welding done using good practice with an E70 electrode, determine the minimum size of the weld required for the following two cases: Welded along the top and bottom edges of the channel only, and Welded along the top, bottom and rear edges of the channel. For both cases, check the tearing stress in the parent material using the same factor of safety.

Solution

Wear and tear is damage that naturally and inevitably occurs as a result of normal wear or aging. It is used in a legal context for such areas as warranty contracts from manufacturers, which usually stipulate that damage from wear and tear will not be covered.

Wear and tear is a form of depreciation which is assumed to occur even when an item is used competently and with care and propermaintenance. For example, repeated impacts may cause stress to a hammer\'s head. This stress is impossible to prevent in the normal use of the tool for its designed task, and any attempt to avert it impedes its functionality. At the same time, it is expected that the normal use of a hammer will not break it beyond repair during a reasonable life cycle.

The phenomenon of wear and tear reflects the second law of thermodynamics, in which objects stray from their original form and function over time unless energy from an external force is used to maintain them. If restoration is impossible an object is regarded as consumable. Parts that are designed to wear inside a machine, like bearings and O-rings are intended to be replaced with new ones; consumables likepaper, cardboard, fabrics, and product packaging are designed with a service life commensurate with their intended use. For example, grocery stores may issue customers a paper or plastic sack to carry out groceries, but it is intended that the sack will have a short lifespan before wear and tear would cause it to fail.

Durable goods (e.g. automobiles, heavy machinery, mainframe computers, musical instruments, handguns, water heaters) are designed with wear parts that are maintained generally by replacement of parts. One way to determine if a good is durable or not is whether a service technician or repairman would typically attempt repairs on it. A specialist may need to be consulted, such as an auto mechanic, a computer technician, a luthier, a gunsmith, or a plumber. An automobile\'s engine may be repairable with a simple adjustment or replacement of a single and inexpensive broken part. Similarly, an electric water heater element that fails from years of wear and tear may be replaced rather than the entire water heater.

In the cardiovascular system, getting out of bed in the morning requires an increase in blood pressure and a reapportioning of blood flow to the head to allow a person to stand up without fainting.12 Blood pressure rises and falls during the day as physical and emotional demands change, providing adequate blood flow as needed. Yet repeated elevation of blood pressure promotes generation of atherosclerotic plaques, particularly when combined with metabolic factors that damage the coronary artery walls.13

For metabolism, glucocorticoids (so named because of their ability to promote conversion of protein and lipids to usable carbohydrates) serve the body well in the short run by replenishing energy reserves after a period of activity, like running away from a predator. Glucocorticoids also act on the brain to increase appetite for food and to increase locomotor activity and food-seeking behaviour,14 thus regulating behaviours that control energy input and expenditure. This effect is useful during manual labour or when playing active sports, but it is not beneficial when someone grabs a pizza and a beer while watching television or writing a paper, particularly when these activities may also be generating psychologic stress. Inactivity and lack of energy expenditure create a situation where chronic elevation of glucocorticoids, resulting from poor sleep, ongoing stress or as side effects of a rich diet, can impede the action of insulin to promote glucose uptake.15Thus, whether it is psychologic stress or sleep deprivation or a rich diet that is increasing the levels of glucocorticoids, the consequences in terms of allostatic load are the same — insulin resistance and increased risk for cardiovascular disease

Whereas an automobile needs consumable fuel and lubricants to operate, components such as tires, seats, and paint are subject to wear and tear and typically are not covered under any warranty when subjected to normal use.