Overstrain

Collapse and Bursting Pressure. If the pressure is sufficiently large to push the plastic—elastic boundary to the outer surface of the cylinder so that the fibers at that surface yield, then there is nothing to restrain the wad, and the cylinder is said to codapse. With an ideal material which does not work harden the codapse pressure, P, sometimes caded the full plastic flow pressure, the full overstrain pressure or the full thickness yield pressure, would be the bursting pressure of the cylinder. It is given by equation 10 when thus... 

A. E. Macrae, Overstrain of Metals and its Application to the Autofrettage Process of Cylinder and Gun Construction, HMSO, London, 1930. 

As contrasted with stress from sustained loads such as internal pressure or weight, displacement stresses may be permitted to cause hm-ited overstrain in various portions of a piping system. When the system is operated initially at its greatest displacement condition, any yielding reduces stress. When the system is returned to its origin condition, there occurs a redistribution of stresses which is referred to as self-springing. It is similar to cold springing in its effects. 

Maximum Reactions for Complex Systems For miiltianchor systems and for two-anchor systems with intermediate restraints, Eqs. (10-105) and (10-106) are not apphcable. Each case must be studied to estimate the location, nature, and extent of local overstrain and its effect on stress distribution and reactions. 

Elastic Behavior The assumption that displacement strains will produce proportional stress over a sufficiently wide range to justify an elastic-stress analysis often is not valid for nonmetals. In brittle nonmetallic piping, strains initially will produce relatively large elastic stresses. The total displacement strain must be kept small, however, since overstrain results in failure rather than plastic deformation. In plastic and resin nonmetallic piping strains generally will produce stresses of the overstrained (plasfic) type even at relatively low values of total displacement strain. 

Uber-heben, v.t. pull over exempt, excuse. — V.T. overstrain be conceited, boast, -heizen, v.t. overheat superheat. tJberhitze,/. excess heat waste heat superheat. 

There is a method that can be used for this analysis. It is extremely complex so it requires using a computer. In general, equations are generated to determine the moment and thrust created in the invert area of the deflected pipe, where a pressure term is superimposed. This analysis must examine the strains in the outer and innermost fibers of the pipe to verify that its wall structure is adequate and not overstrained. During this analysis the pipe must be examined under conditions of no pressure, minimum pressure, and maximum pressure. 

Overstrained Behavior. Stresses cannot be considered proportional to displacement strains throughout a piping system in which an excessive amount of strain may occur in localized portions of the system (an unbalanced system). Operation of an unbalanced system in the creep range may aggravate the deleterious effects due to creep strain accumulation in the most susceptible regions of the system. Unbalance may result from one or more of the following ... 

In brittle nonmetallics (such as porcelain, glass, impregnated graphite, etc.) and some thermosetting resins, the materials show rigid behavior and develop high displacement stresses up to the point of sudden breakage due to overstrain. 

This is also true for the calculation of the internal pressure pei at which the elastic behavior ends and the plastic deformation (overstrain) begins, based on the GE (v. Mises) hypothesis a (proof stress in N/mm2, pei = internal pressure in N/mm2, u diameter ratio)... 

A choice of strains is given, with 100% the preferred value the most usual test time is 24 h and the test temperature is commonly 70°C or 100°C. The test piece is strained at between 2 and 10 mm/s and the reference length measured between 10 and 20 min later. If it does not fall within given tolerances about the nominal strain, the test piece is rejected. Presumably, if appreciable relaxation occurs in this period, it may be necessary to overstrain initially with test pieces clamped well outside of the reference length. For... 

The effects of chronic hypertension on the human organism are, with one exception, of little interest to the investigator studying pathogenesis, although of great import to the sufferer and his physician. That exception is failure of the kidneys. Disease and failure of the heart are probably caused by chronic overstrain, often associated with another metabolic disease, arteriosclerosis of the coronary arteries. They account for about two thirds of the deaths primarily due to hypertension. Strokes of apoplexy, or cerebral vascular accidents, from rupture or thrombosis of a cerebral artery weakened by disease cause another sixth, uremia about one twelfth, and other conditions the remainder (28). Except for uremia, these events are usually the result of overwork and increased arterial tension. Only rarely does the heart escape hypertrophy. 

An overstrained transmission grid is vulnerable to a loss of service at any location for example, in early April 2001, a windstorm knocked out a transmission line between the Northwest and Southern California, depriving Los Angeles of 3,000 megawatts of transmission capacity for ten days and causing a Stage 2 emergency. 

CED must also execute many small projects that, if handled in the conventional way, would increase cost and overstrain the limited in-house resources. These projects are assigned to versatile, hands-on engineers (not necessarily experienced project managers) capable of performing personally some of the activities involved in project execution and control. 

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