Compression after impact strength

Farley. G.L. and Dickinson. L.C. (1992). Removal of surface loop from stitched composites can improve compression and compression-after-impact strengths. J. Reinforced Plast. Composites 11. 633-642. 

Figure 9.12 Normalised stress versus cycles for failure with compression stress normalised against compression after impact strength 25% and 50% refer to damage as a % of sample width.

Davies GAO, Hitchings D. The separate roles of fibre damage and delamination in compression-after-impact strength of composite panels. In 5th EUROMECH Solid mechanics Conf. Thessaloniki, Greece 2003. 

It is critical that surface treatment conditions be optimized to composite properties since overtreatment as well as undertreatment will degrade composite properties. Typically composite interlaminar shear strength (ILSS), in-plane shear, and transverse tension ate used to assess the effectiveness of surface treatment. More recently damage tolerance properties such as edge delamination strength, open hole compression, and compression after impact have become more important in evaluating the toughness of composite parts. 

Fig. 8.8. Correlation of residual compression-after-impact (CAI) strength with resin flexural strain to...

The resin has good adhesion to glass and carbon fibers and shows a lower coefficient of thermal expansion than epoxies and most plastics. As a matrix resin in a carbon composite, PEAR is said to surpass epoxy (Hercules/Hexcel 3501-6) by 48% in tensile, compression, hot/wet, compression-after-impact, and other fiber-dominated properties. Shear strength (matrix-dominated property) is reported at 50% higher than epoxy at room temperature and up to 80% higher under hot-wet conditions. 

The compression after impact (CAI) test was conducted to evaluate the residual strength after impact and the healing efficiency after confined shape recovery. Previous studies [70,71] have... 

Compressive strength after impact (MPa) Open-hole compressive strength (MPa) 332... 

As can be seen from the results, the composite formed from monomer/-polymer 114a with Celion G30-500 8HS fabric exhibited excellent mechanical properties [28], To a first approximation it would appear that the inherent fracture toughness of the matrix resin has been carried over to the composite panels. The CAI (compressive strength after impact) and OHC (open hole compression) tests are a direct measurements of the toughness of the composite part, the value of 332 MPa for the CAI compares very favorably to the value of 300 MPa typical for the thermoplastic composites. The OHC values under hot-wet test conditions would seem to indicate that the composite has very good retention of its mechanical properties at both 177°C and 203 °C. 

Heat-Stabilized Compressed Wood (Staypak). Pressures of 400-4000 psi are applied to the wood after it has been heated. Both heat and pressure plasticize wood. At 160 °C and 12% moisture content, the maximum plastic yield per increment of pressure occurs at 1100 psi. Pressures of 1500-2500 psi are required to yield a specific gravity of 1.3. Highly densified wood must be cooled in the press. Some strength properties, such as impact strength and hardness, are increased in direct proportion to the density. Staypak finds limited application for silverware handles and desk legs (6). 

OHT open-hole tensile OHC open-hole compression CAI compression strength after impact EDS edge delamination strength. (Adapted from Table 4 in Pilato, L.A. Michno, M.J. Advanced Composite Materials Springer-Verlag Berlin, 1994 118.)... 

A recent study [17] subjected a population of samples of quasi-isotropic (QI) CFRP laminate to identical impacts and then to residual strength tests to measure the CAI. Significant variability in CAI values was found. The coefficient of variation (CoV — the standard deviation/mean) of the compression strength increased from 1.8% before impact to 5.4% after impact. Fitting the distribution of strength to a... 

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