Fig。 2。 Stress vs。 strain performance in static tests of CM and AWJM specimens。 (For interpretation of the references to color in this figure legend, the reader is referred

to the web version of this    article。)

Fig。 1。     Experimental setup for fatigue  tests。 (For  interpretation of the references  to  color  in this figure legend,  the reader is referred  to  the web  version of this article。)

Fig。 3。 Comparison of the evolution of the damage for various level of loading for (a) conventional machining and (b) abrasive water jet machining。 (For interpretation of the references  to  color in this figure legend,  the  reader is referred  to the  web version  of this  article。)

Fig。 4。 Damage vs。 cycles at 10 kN (59% UTS) fatigue loading for all specimens。 (For interpretation of the references to color in this figure legend, the reader is referred  to the web version of this    article。)

the jet and craters damage due to the impact of the abrasive on the fibers。 Globally these damages are uniformly distributed on the hole of the wall。 However, for specimens drilled with a conven- tional drill bit, surface roughness photographs show the presence of fiber pull out areas and matrix degradation non-uniformly dis- tributed。 These pullout areas are related to material removal mech- anisms which are strongly influenced by the relative angle between  the  direction  of  the  cutting  speed  and  the  direction of

the fibers (Fig。 6)。 In this case, the maximum damage due to fibers pull out is observed when plies are oriented at —45° compared to the direction of the cutting speed。 However the minimum damage is located in the zone where the fibers form an angle of +45° com- pared to the direction of the cutting speed。 These observations are in a good agreement with previous work conducted by various authors [10,36] on the orthogonal cutting of UD composite specimens。

The main cause of the difference in the damage accumulation between the CM and AWJM specimens is due to the surface quality as shown in the machined surface images obtained before fatigue tests (Figs。 5 and 6) and also confirmed by SEM images of machined surface obtained after fatigue tests (Figs。 7 and 8)。 Fig。 7a illustrates the presence of crack propagation phenomena due to the initial damages (fiber pullout and matrix degradation) induced by the interaction between the machining tool and the carbon fibers as shown in the SEM observation mentioned previously (Figs。 5 and 6)。 These cracks were propagated due to the shear between the planes owing to the axial mechanical load in composite with stack- ing sequence of [±45°]。 It is worth mentioning that the matrix deg- radation and fiber pullout in CM specimens affected the fiber– matrix load transfer, consequently, that led to significant material degradation under tensile loading conditions。 SEM images pre- sented in Fig。 8 showed streak marks in the direction of the water jet after fatigue loading。 There was no visible crack or delamination in this observed area (Fig。 8)。 The final failure of the AWJM speci- men occurred according to that two stages, explain in Section 3。2。1。

Fig。 5。  Cartography of the surface roughness of the wall of the hole for different specimens。 Circular hole obtained with (a) conventional machining using a cutting tool and

(b) with abrasive water  jet。 (For  interpretation of the  references  to color  in this figure legend,  the reader  is referred to  the  web version of this    article。)