Load limits indicate the maximum weight an item can carry before plastic deformation, and there are different types of limits. The working load limit is the safe extent, based on the test load limit, and the item’s lifespan varies. Shock load limits are also important, and age and environmental factors must be considered. Exceeding limits can cause deformation, collapse, and breakage.
A load limit is the amount of weight an item can withstand before it results in plastic deformation. There are different types of load limits and breaking points for a given item. In general, the workload limit is the only one the customer needs, but others are useful too. Load limits do not take into account environmental effects and age; these factors must be considered by the endpoint customer at load time. A common result of exceeding load limits is deformation, collapse and breakage.
Almost any metal structure or object is at risk of plastic deformation. This type of deformation is different from common bending or stretching. Once a substance reaches the point of plasticity, it does not return to its normal shape. To prevent items from reaching this point, systems have maximum load limits. Under optimal conditions, these limits prevent the occurrence of plastic deformations.
When people refer to a load limit, they typically mean the working load limit. This is the extent to which the item is safe from plastic deformation. If kept at this limit, the item should be safe for its entire life. The exact life span of an item is a specific period of time, usually in years, which varies widely by item. While many items continue to be used beyond their life expectancy, their carrying capacities are no longer supported beyond that point.
The working load limit is based on the test load limit. The test load is an amount of weight the item carried when brand new and unused. This limit is then reduced by half for the working limit. Proof load is the extreme point of weight an item can handle and should never be used as a limit by a consumer. Total test load decreases rapidly with age and use.
Some items also have a shock load limit. This is the weight limit that can be placed on the object when the user intends to have sudden or jerky movements. When a load is suddenly moved, its weight transfers differently to the object it is on. For a few milliseconds instead of weighing as it normally would, it can weigh significantly more or less. Those few milliseconds can cause plastic deformation and breakage.
There are two main points that every end user should take into consideration when reading load limits. The first is the age of the item. Any item beyond its intended useful life is no longer governed by its weight limit. The other is the environment. Load limits are put together in a laboratory environment, extreme heat and cold can weaken a structure. Other environmental factors, such as the humidity of the area, can have major impacts on some metals and should not be discounted even when the item is new.
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