creep

(redirected from The Creep)
Also found in: Dictionary, Thesaurus, Medical, Legal.

creep

1. Geology the gradual downwards movement of loose rock material, soil, etc., on a slope
2. a slow relative movement of two adjacent parts, structural components, etc.
3. slow plastic deformation of metals

creep

[krēp]
(electronics)
A slow change in a characteristic with time or usage.
(engineering)
The tendency of wood to move while it is being cut, particularly when being mitered.
(geology)
A slow, imperceptible downward movement of slope-forming rock or soil under sheer stress.
(graphic arts)
A forward movement of the blanket during offset printing.
(mechanics)
A time-dependent strain of solids caused by stress.
(mining engineering)

Creep (materials)

The time-dependent strain occurring when solids are subjected to an applied stress. See Stress and strain

Some of the different kinds of creep phenomena that can be exhibited by materials are shown in the illustration. The strain ε = ΔL/L0, in which L0 is the initial length of a body and ΔL is its increase in length, is plotted against the time t for which it is subjected to an applied stress. The most common kind of creep response is represented by the curve A. Following the loading strain ε0, the creep rate, as indicated by the slope of the curve, is high but decreases as the material deforms during the primary creep stage. At sufficiently large strains, the material creeps at a constant rate. This is called the secondary or steady-state creep stage. Ordinarily this is the most important stage of creep since the time to failure tf is determined primarily by the secondary creep rate s. In the case of tension creep, the secondary creep stage is eventually interrupted by the onset of tertiary creep, which is characterized by internal fracturing of the material, creep acceleration, and finally failure. The creep rate is usually very temperature-dependent. At low temperatures or applied stresses the time scale can be thousands of years or longer. At high temperatures the entire creep process can occur in a matter of seconds. Another kind of creep response is shown by curve B. This is the sort of strain-time behavior observed when the applied stress is partially or completely removed in the course of creep. This results in time-dependent or anelastic strain recovery.

Typical creep curves for materialsenlarge picture
Typical creep curves for materials

Creep of materials often limits their use in engineering structures. The centrifugal forces acting on turbine blades cause them to extend by creep. In nuclear reactors the metal tubes that contain the fuel undergo creep in response to the pressures and forces exerted on them. In these examples the occurrence of creep is brought about by the need to operate these systems at the highest possible temperatures. Creep also occurs in ordinary structures. An example is found in prestressed concrete beams, which are held in compression by steel rods that extend through them. Creep and stress relaxation in the steel rods eventually leads to a reduction of the compression force acting in the beam, and this can result in failure. See Prestressed concrete

The mechanism of creep invariably involves the sliding motion of atoms or molecules past each other. In amorphous materials such as glasses, almost any atom or molecule within the material is free to slide past its neighbor in response to a shear stress. In plastics, the long molecular chains can slide past each other only to a limited extent. Such materials typically show large anelastic creep effects (curve B in the illustration).

For crystalline materials, creep deformation also involves the sliding of atoms past each other, but here the sliding can occur only within the cores of crystal dislocations. Thus, creep of metals and ceramics is usually governed by the motion of dislocations.

It is possible to design materials with superior creep resistance. When solute atoms are added to metals, they are attracted to the strain fields of the dislocations. There they inhibit dislocation motion and in this way improve the creep resistance. Many of the aluminum alloys used for aircraft structures are strengthened in this way. The addition of second-phase particles to alloys is another way to improve the creep resistance. The most effective strengthening phases are oxides, carbides, or intermetallic phases, because they are usually much stronger than the host metal and therefore create strong obstacles to dislocation motion. Materials containing finely dispersed, strong particles of a stable phase are usually very creep-resistant. Nickel-based superalloys, used in gas-turbine engines, derive their creep resistance from these effects. See High-temperature materials, Metal, mechanical properties of

creep

1. The continuing, time-dependent part of strain resulting from stress; the permanent and continuing dimensional deformation of a material under a sustained load, following the initial instantaneous elastic deformation.
2. Slow movement of rock debris or soil, usually imperceptible except in observations of long duration.
3. In structures, particularly of concrete, permanent deflection of structural framing or structural decking resulting from plastic flow under continued stress.
4. In roofing, permanent elongation or shrinkage of a roofing membrane resulting from thermal or moisture changes.
5. The flow of water along the interface between a structure and the surrounding soil or rock foundation.

creep

creep
Normal position of creep marks.
creep
Tire needs replacement.
creepclick for a larger image
i. The gradual rotation of a tire around a wheel. To detect creeping, white index marks are made on tires and wheels and are called creep marks. Some tires have two molded arrows in between which creep marks are painted.
ii. The property of a metal that allows it to be permanently deformed when subject to stress (e.g., turbine blades that operate at temperatures at which creep can become serious). Creep increases with temperature, duration, and magnitude of force.
Primary creep, stage 1, is a period of decreasing creep rate. Primary creep is a period of primarily transient creep. During this period deformation takes place and the resistance to creep increases until stage 2. Secondary creep, stage 2, is a period of roughly constant creep rate. Stage 2 is referred to as steady state creep. Tertiary creep, stage 3, occurs when there is a reduction in cross sectional area due to necking or effective reduction in area due to internal void formation.
References in periodicals archive ?
The strong nonlinearity exhibited by LLDPE nanocomposites and the increase of the creep compliance with applied stress suggests the applicability of the TSSP.
The fully-reversed cyclic shear loading also induced oscillating response of the normal creep strain and significantly increases the creep deformation compared with the pure normal stress creep test data (Fig.
Recently, the creep behavior of PMR-15 resin was studied at a temperature 550 K by the researchers at the Air Force Research Laboratory's Materials and Manufacturing Directorate.
To understand the process of the creep failure, the true stress-true strain dependence must be determined.
In general, for a constant stress, [sigma], the creep compliance J(t) can be written as the ratio of the strain ([epsilon]) to stress at a certain time (t) as follows:
10 and 11, the creep behavior of a linear viscoelastic laminate subjected to a constant load [N.
Therefore, the exponential form of the creep compliance function is referred to as multi-Kelvin approach.
The stresses employed for the creep testing were 11.
Our principal objectives were (i) to fit the nonlinear tensile creep of these blends with a suitable equation, (ii) to apply the time-strain superposition involving the strain-induced free volume and (iii) to develop a predictive format appropriate for the creep of binary blends with co-continuous components showing nonlinear creep behavior.
DENVER, July 28, 2015 /PRNewswire/ -- Gravitas Ventures, an international, independent film distributor, announces the worldwide release of the film The Creep Behind the Camera on August 4, 2015 on video on demand and pay per view (VOD/PPV).
The creep prediction study showed that the polycarbonate resin had a projected lifetime of 3.
5] and external parameters (applied stress, temperature, and humidity) [2], For wood/plastic composites, research has shown that adding wood fibers (WF) to pure polymers greatly improves the creep resistance of the matrix polymer, with the relative creep of the composites decreasing with increasing WF concentration [6], However, When Xu et al.