Compression after impact

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...

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. 

Leong, K.H.. Herszberg, I. and Bannister, M.K. (1996). An investigation of fracture mechanisms of carbon epoxy laminates subjected to impact and compression-after-impact loading. In Proc. 1st Australasian Congress on Applied Mechanics, Melbourne, pp, 315-320. 

In Table 7, typical key laminate properties for thermoset and thermoplastic composites are given. It is immediately apparent that suitable toughening (discussed previously) can achieve superior compression after impact and comparable edge delamination... 

Susceptibility to interlaminar failure is a major weakness of advanced laminated composite materials. It can occur by in-plane shearing (i.e., sliding) (mode II). and out-of-plane shearing (i.e.. tearing) (mode III) as well as by tensile (mode I) deformation. Mode II loading is of particular interest, as values have been shown to correlate with compression after impact data [142.143]. which is required for such purposes as civil aircraft certification. 

Figure 9.5 Failure mechanisms for compression after impact .

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. 

Cartie DDR, Irving PE. Effect of resin and fibre properties on impact and compression after impact performance of cfrp. Composites Part A 2002 33 483-93. 

Gower MRL, Shaw RM. Assessment of the applicability of compression after impact (CAI) and open hole tension (OHT) methods for use under fatigue loading. In 13th European conference on composite material, Stockholm Sweden 2008. 

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. 

Crack Closing Efficiency in Terms of Compression after Impact Test... 

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... 

Table 4.2 summarises some basic properties of PEEK-based APC2 thermoplastic composites from Cytec. The properties of finished components can be tailored by controlling fibre orientation during the layup process. Eull characterisation of a thermoplastic composite will include measurement of in-plane shear properties, open hole tensile and compressive failure, interlaminar fracture toughness and compression after impact. Cytec also produces TPC based on PEKK [20]. 

Impact Instmmented drop-weight impact Tensile impact Compression after impact (Boeing BSS-7260)... 

S. M. Lee (1986) Compression-after-impact of composite with toughened matrices, SAMPE Journal, 64. 

---