PSI - Issue 28

Najat Zekriti et al. / Procedia Structural Integrity 28 (2020) 1745–1754 Najat Zekriti and al/ Structural Integrity Procedia 00 (2019) 000–000

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1. Introduction The failure behavior of cracked structures is characterized by the stress field in the vicinity of the tip Irwin (1957). Fracture mechanics emphasizes on stress intensity factors (SIF), which define the singular stress field in front of the end of a crack and control the fracture of a sample when a critical stress intensity factor is achieved. Since the stress field by the near-tip takes important values, there will therefore be plastic deformations at the bottom of the crack, which will be more or less extensive depending on the ductility of the material and will strongly influence the breaking behavior N. Recho (1995) SIF can be obtained from numerical measurement of the stress and displacement field near the crack. Different techniques can be used to measure displacement or deformation fields Grédiac and Hild(2011). When they use optical bases and are coupled with mechanical analysis, we often speak of photomechanics Berthaud et al (1995). Photoelasticity is the oldest Jessop and Harris (1949). Still widely practiced in the industrial world. One of the popular measurement techniques using pictures is digital image correlation (DIC). Developed since the 80s by Sutton and al. (1983) (2009) Chu and al (1985). The image correlation technique is a non-contact optical method for measuring kinematic fields. This method offers the possibility of determining the displacement and deformation fields at any point on the surface of the objects, based on the comparison of two images taken at different loading steps one called the reference, the other corresponding to the deformed state Pan and al. (2009) Many composite and plastics has been used by this methodology including 3D-printed material; Huang and al. (2013) Shahrubudin and al. (2019). Among the various 3D printing techniques, Fused Deposition Modeling (FDM) is one of the most famous AM technologies in the world today. It has larger consumer due of its reliability, wide range of usable materials, safety and manufacturing simplicity, lower cost of machines and materials and lower process temperatures. Olivera and al (2016) Kannan and Senthil kumaran (2014). In this manuscript the polymer studied is Acrylonitrile butadiene styrene (ABS) extruded and the other one printed using Fused Deposition Modeling (FDM); The choice of this technique by cause of its reliability, safety and manufacturing simplicity, lower cost of machines and lower process temperatures. This following work is a contribution to the study of the mechanical behavior of ABS under uniaxial tensile loading, taking on board the influence of damage. The aims of this work is to study and compare the behavior of extruded ABS and printed one through two parts. The first part will be dedicated to study the influence of the crosshead speed in traction on the behavior of the material; this study will be done from a series of experiments on ABS extruded and printed specimens subjected to different crosshead speeds at room temperature. The second part will evaluate the displacement and stress fields at the v-notch through an experimental analysis based on the digital image correlation technique, using the Ncorr software implemented on MATLAB. Thus, the stress intensity factor is calculated. The results generated by Ncorr are in good agreement with the empirical formulas.

Nomenclature a

crack length

t

time

σ w

nominal stress

width of the specimen plane deformations distance from the crack tip

k

r

β

life of fraction

KI stress intensity factor SENT single edge notched tensile ABS acrylonitrile butadiene styrene