a b s t r a c t   The influence of the machining quality on the mechanical behavior of CFRP composites is yet not fully understood。 There are only few works in the literature that have investigated the effect of the machining quality on CFRP。 In fact, most of these works focus only on conventional machining such as axial or orbital drilling。 The aim of this paper is to examine the influence of two machining processes namely conven- tional machining (CM) and abrasive water jet machining (AWJM) on the mechanical behavior of compos- ite plates under cyclic loading。 For this purpose, an experimental study using several composite plates drilled with a cutting tool and an abrasive water jet machining was carried out。 In order to study the impact of the process of machining on the mechanical behavior, thermographic infrared testing and fati- gue cyclic tests were performed to assess temperature evolutions, stiffness degradation, and the damage evolution in these plates。 Fatigue testing results have shown that the damage accumulation in specimens drilled with CM process was higher than the AWJM specimens。 Furthermore, the endurance limit for a composite plate drilled with CM was approximately 10% inferior compared to specimens drilled with AWJM。 This difference can be related to the initial surface integrity after machining induced by the dif- ference in the mechanism of material’s removal between the two processes  used。86004

1。Introduction

Currently, composite materials are used within primary load carrying aircraft structures。 Recent examples are the Boeing 787 and Airbus A350XWB in which the composite weight content has increased to 50–60% [1–4]。 For such applications of carbon fiber reinforced plastics (CFRP), the machining of reliable, and damage tolerant fastener holes is a challenging task [5]。 A bolted or riveted joint transfer load within the structure and its lifetime is depen- dent upon the quality and accuracy of the hole。 Damage-free machining of holes results in increased fatigue life of composite structures [6]。 Different conventional machining techniques used for composite materials are drilling, milling, sawing, routing, and grinding using applicable tools and operating environments。 Tech- niques using abrasive water jet, laser and ultrasonic machining are considered to be non-conventional  [7–10]。

Drilling is a commonly used technique in the aircraft industry for producing holes [11,12]。 Several works have been keen on the analysis of delamination at the entry and the exit of the hole in- duced by the interaction between the cutting tool (conventional

⇑   Corresponding  author。

E-mail  address:  redouane。zitoune@iut-tlse3。fr  (R。 Zitoune)。

machining) and the composite material。 A number of works show that this damage is influenced by the choice of the machining parameters, the geometry of the cutting tool tip [13–15], and the nature of its material as well as the process  of manufacturing of the composites parts [16–18]。 Khashaba [19] observed that low coefficient of thermal conduction and a low transition temperature leads to increase in the temperature produced during drilling of polymeric composite materials。 This generated heat, accumulated around cutting tool edge resulted matrix degradation and thermal damages。 Manna [20] investigated that the spindle speed has most significant parameter that has the highest effect on surface rough- ness height (Ra) followed by the feed rate。 Similarly Kilickap [21] observed the influence of cutting speed and feed rate on the delam- ination of machined hole。 It was concluded that the higher feed rate and cutting speed has the highest influence on the damage。 Gaitonde et al。 [22] observed that the feed rate is linearly related  to the damage while cutting speed behaves non-linearly with dam- age at entrance of the hole。 Davim et al。 [23] have shown that, dur- ing drilling of composite part made of carbon fiber reinforced plastics with cutting tool the damage area increases when cutting speed increases from 50 to 70 m/min。 In addition, it was also men- tioned that the use of digital analysis is suitable for the evaluation of the damages induced by machining。 Campos Rubioa et al。 [15]