Compression failure

Answers E ° /p for external-pressure buckling <7f/p for yield or brittle compressive failure. 

In addition to their exceptional tensile strengths, PAN-based carbon fibers are far more resistant to compressive failure than are their pitch-based counterparts or polymeric high-performance fibers. However, because the PAN precursor is not... 

Hence an applied stress of Oj, = 92 MN/m would initiate a shear failure before tensile or compressive failures occurred. 

When the buekling load is smaller than the load that will cause the column to fail under compression, it is called a thin or slender column. If compressive failure oecurs first, it is ealled a short column. 

Kendall, K. (1978). Complexities of compression failure. Proceedings of the Royal Society of London, A 361, 245-63. 

Sohi. M.M., Hahn, H.T. and Williams, J.G. (1987). The effect of resin toughness and modulus on compressive failure modes of quasi-isotropic graphite/epoxy laminates. In Toughened Composites. ASTM STP 937 (N.J. Johnston cd.). ASTM. Philadelphia, PA. pp 37 60. 

Some of the best uses of Kevlar are in aircraft composites and flak jackets for military and police uses, which require high tensile strength and high modulus per unit of weight. It also has the property of damage tolerance, as it has a ductile compressive failure mode, which is very different from the brittle failure of carbon fibers. 

Hahn, H. T., Williams, J. G. Compression Failure Mechanisms In Unidirectional Composites, NASA TM 85834 (1984)... 

A specimen can fail in compression, tension, or shear. A specimen that fractures at 45% to the longitudinal axis has failed in shear (Lelievre et al., 1992). Tensile failure results if the specimen fractures at 90% to the longitudinal axis, and compressive failure is represented by fracture along the longitudinal axis (Lelievre et al., 1992). 

Composite structure of fibres, 33 Composition parameter, 858 Comprehensive tables, 858 Compressibility, 224,385 Compressional waves, 390-1 Compression (bulk) modulus, 514 Compressive failure, 834 Compressive strength, 835 Concept... 

Figure 4.26 Compressive failure models in high-petformance fibers (a) micro-buckling model and (b) misorientation model (after Kozey and Kumai 1994).

In all the S4/0 specimens the delamination crack stops after only 5 mm of propagation in the pinned block. The failure mode then changes from delamination crack propagation to a bending failure of the arms. The toughness at the time of failure is 7000 J/m. TTie calculated bending stress in the beam is (Tb=l lOOMPa. The local curvature leads to a compressive failure strain in the outside layers of 1.3%. 

G-fibers may contain minute wall dislocations or axial compression failures. 

Maximum compressiva. stress, due to creep / and compression / failures over time... 

Figure 10.6. Bending of timber beams, (a) Schematic stress distribution at the mid-span of the beam, assuming that the beam deforms elastically, (b) In practice, clearwood starts buckling due to compression failures at the upper surface, whereas knotty timber is more likely to fail in a brittle manner in the vicinity of a knot lying in the tension zone. The behaviour of knotty timber is more akin to a beam deforming elastically up to brittle failure (rupture).

Figure 10.7 (a) Failure lines for grouted and ungrouted granular soils, (b) Drained triaxial test results for silicate grouted coarse and medium sands. (From Ref. 11.15.) (c) Typical stress-strain curve from unconfined compression test on chemically grouted sand, (d) Compression versus time data for creep test on chemically grouted sand, under constant load, (e) Failure time versus percent of unconfined compression failure load. (+) indicates unconfined compression tests, and ( ) indicates triaxial tests with S3 = 25% of Si. 

The compressive failure of oxide scales has been investigated comprehensively in [6-8], According to the analysis by Evans and Lobb [6], there are two main routes to spalling - scale buckling and wedging. 

Veeken et al. (24) reviewed predictive models for solids production. Their assessment was that modeling of compressive failure is only qualitatively useful. This is because of the sensitivity of the results to the choice of yield envelope and failure criterion. Even so, this approach can be used to develop perforation strategy (density, phasing, and size), to select the stronger zones for perforation, and to provide guidelines for operation of a well (e.g., pressure drawdown, flow rate). 

---