Residual stresses are stresses in material which are introduced during the processing phase but endure after the product is finished, instead of resolving once the source of the stress is removed. One could think of residual stresses as stresses which are left behind in manufactured components. Sometimes these stresses are deliberately introduced to hold parts in tension for the purpose of prolonging wear life and providing other features. In other instances, residual stresses are introduced by accident and they are not desirable. Processing of materials like metals and plastics often involves heat, which can contribute to the development of residual stresses. Welding residual stress, for example, is a problem with some metal components. Likewise, stresses can be created with plastics which are heated and injection molded. Other processes like rolling can create similar stresses in the materials they are used to shape or otherwise work. When a residual stress is not desired and carefully controlled, it can become a problem. Components might fail as a result of residual stress which is not controlled; a bolt might blow apart without any pressure, for instance. Residual stresses are sometimes blamed for incidents like bridge failures when no other causes can be determined. These stresses are hard to measure, especially after a component failure has damaged a part, making it difficult to study and hard to distinguish the cause of cracking and other problems. In other instances, residual stresses are actually wanted. A classic example is the stress associated with hammering in a nail. When a nail is hammered into wood, the residual stresses created through the process are what holds the nail in instead of allowing it to pop back out. Likewise, blades and other metal components are often made with residual stresses to limit cracking and fatigue. In these cases, careful calibrations are performed to determine the desired level of stress and control for it during production so that components will be produced with the specified characteristics. Equipment which can be used to take residual stress measurements is available. Measuring such stress is tricky because most equipment is designed to measure ongoing stress,
Residual stresses are stresses in material which are introduced
during the processing phase but endure after the product is
finished, instead of resolving once the source of the stress is
removed. One could think of residual stresses as stresses which are
left behind in manufactured components. Sometimes these stresses
are deliberately introduced to hold parts in tension for the
purpose of prolonging wear life and providing other features. In
other instances, residual stresses are introduced by accident and
they are not desirable.Processing of materials like metals and
plastics often involves heat, which can contribute to the
development of residual stresses. Welding residual stress, for
example, is a problem with some metal components. Likewise,
stresses can be created with plastics which are heated and
injection molded. Other processes like rolling can create similar
stresses in the materials they are used to shape or otherwise
work.When a residual stress is not desired and carefully
controlled, it can become a problem. Components might fail as a
result of residual stress which is not controlled; a bolt might
blow apart without any pressure, for instance. Residual stresses
are sometimes blamed for incidents like bridge failures when no
other causes can be determined. These stresses are hard to measure,
especially after a component failure has damaged a part, making it
difficult to study and hard to distinguish the cause of cracking
and other problems.In other instances, residual stresses are
actually wanted. A classic example is the stress associated with
hammering in a nail. When a nail is hammered into wood, the
residual stresses created through the process are what holds the
nail in instead of allowing it to pop back out. Likewise, blades
and other metal components are often made with residual stresses to
limit cracking and fatigue. In these cases, careful calibrations
are performed to determine the desired level of stress and control
for it during production so that components will be produced with
the specified characteristics.Equipment which can be used to take
residual stress measurements is available. Measuring such stress is
tricky because most equipment is designed to measure ongoing
stress, such as tension created by the use of a tool. Stress which
is essentially locked into a component is more difficult to
measure. Companies which manufacture equipment which can be used
for residual stress measurement may also offer materials testing
services which allow companies to send out components for testing
rather than conducting their own tests.
