Compressive loading

The reference sample in form of a cylinder or bar with probe placed on top of it, is subject to tensile or compressive loading using strength machine ( Instron type). 

Plastic Forming. A plastic ceramic body deforms iaelastically without mpture under a compressive load that produces a shear stress ia excess of the shear strength of the body. Plastic forming processes (38,40—42,54—57) iavolve elastic—plastic behavior, whereby measurable elastic respoase occurs before and after plastic yielding. At pressures above the shear strength, the body deforms plastically by shear flow. 

As with other plastics materials, temperature has a considerable effect on mechanical properties. This is clearly illustrated in Figure 13.5 in the case of stress to break and elongation at break. Even at 20°C unfilled PTFE has a measurable creep with compression loads as low as 3001bf/in (2.1 MPa). 

Often, Hertz s work [27] is presented in a very simple form as the solution to the problem of a compliant spherical indentor against a rigid planar substrate. The assumption of the modeling make it clear that this solution is the same as the model of a rigid sphere pressed against a compliant planar substrate. In these cases, the contact radius a is related to the radius of the indentor R, the modulus E, and the Poisson s ratio v of the non-rigid material, and the compressive load P by... 

Ur, Ur, and u- are the cartesian results Ur and u- are the results in cylindrical co-ordinates. Note u is in the direction of positive P, pressing into the half plane for compressive loading. The tangential displacements of the free surface are towards the origin in agreement with our intuition. 

A polypropylene bar with a square section (10 mm x 10 mm) is 225 mm long. It is pinned at both ends and an axial compressive load of 140 N is applied. How long would it be before buckling would occur. The relationship between the buckling load, Fc, and the bar geometry is... 

A polypropylene rod, 150 mm long is to be designed so that it will buckle at a critical strain of 0.5%. C culate a suitable diameter for the rod and the compressive load which it could transmit for at least one year. 

Note Once again the strain is less than 0.5% so no correction is needed for compressive loading). 

Under compression loading, the long flexible tension specimens would simply buckle. Thus, lateral support to prevent buckling is necessary as shown in the compression test fixture with side-support plates in Figure 2-24. There, the specimen is essentially as long as the fixture is tall, and only a small portion of the specimen can be seen where it is not supported. 

Most comparisons of a failure criterion with failure data will be for the glass-epoxy data shown in Figure 2-36 as a function of off-axis angle 0 for both tension and compression loading [2-21]. The tension data are denoted by solid circles, and the compression data by solid squares. The tension data were obtained by use of dog-bone-shaped specimens, whereas the compression data were obtained by use of specimens with uniform rectangular cross sections. The shear strength for this glass-epoxy is 8 ksi (55 MPa) instead of the 6 ksi (41 MPa) in Table 2-3. 

Most components of the strength tensors are defined in terms of the engineering strengths already discussed. For example, consider a uniaxial load on a specimen in the 1-direction. Under tensile load, the engineering strength is Xj, whereas under compressive load, it is (for example, Xg = -400 ksi (-2760 MPa) for boron-epoxy). Thus, under tensile load. 

Laminated composite plates under in-plane tensile loading exhibit deformation response that is both like a ductile metal plate under tension and iike a metai plate that buckles. That is, a composite plate exhibits progressive faiiure on a layer-by-layer basis as in Figure 4-34. Of course, a composite plate in compression buckles in a manner similar to that of a metal plate except that the various failures in the compressive loading version of Figure 4-34 could be lamina failures or the various plate buckling events (more than one buckling load occurs). 

A plate buckles when the in-plane compressive load gets so large that the originally flat equilibrium state is no longer stable, and the plate deflects into a nonflat (wavy) configuration. The load at which the departure from the flat state takes place is called the buckling load. The flat equilibrium state has only in-plane forces and undergoes only ex-... 

RB-90 reverse buckling disk. Pressure on CONVEX side of disk and patented seating design puts compression loading on disk metal. 

Buttress threads are designed to resist high axial tension or compression loading in addition to offering resistance to leakage. 

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