PSI - Issue 42

Mohamed M.A. Ammar et al. / Procedia Structural Integrity 42 (2022) 1328–1335

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Mohamed Ammar / Structural Integrity Procedia 00 (2019) 000–000

Creel System

Prepreg Tow

Control Unit

Robot

Force/Torque Sensor

Robot

Hot Gas Torch

Specimen

Fig. 2: The robot arm integrated with the automated fiber placement head.

forces for all the samples. A path planning algorithm is proposed to manufacture the angle-ply composite laminates. The trajectory generation approach is based on the procedure introduced in Ammar et al. (2020). The C ++ programs are created and uploaded to the robot controller to perform the process. The flat panels are then produced and subjected to an autoclave curing process based on the required procedure for the utilized epoxy. Fig. 3 presents one set of the fabricated thermoset composite samples. The fabricated samples are then left for relaxation. Subsequently, the incremental hole-drilling method is used to estimate the induced residual stresses for each specimen based on the measurement process introduced in Ammar et al. (2021a). As reported in Pagliaro and Zuccarello (2007); Serra et al. (2014), the hole-drilling technique depends mainly on measuring the strains caused by relief of the residual stresses in a shallow hole in the composite component. The principle of this methodology is based on removing some of the stressed materials, followed by movements of the surrounding material to re-adjust themselves to reach the new equilibrium state. Thus, a set of calibration parameters are defined numerically and used to calculate the stresses based on the measured strains taking into consideration the e ff ect of the specimen geometry as well as the drilling process.

4. Results and discussion

This section presents the results of the microstructure analysis of the composite laminates in order to explain the e ff ect of the plies’ configurations on their boundary conditions and the subsequent e ff ect on the induced residual stresses. It also presents the residual stresses’ data for di ff erent laminate configurations. Several multi-axis samples are fabricated with the configurations of [-45 o , -45 o , 45 o , 45 o ], [45 o , -45 o , 45 o , -45 o ], [0 o , 0 o , 90 o , 90 o ], and [0 o , 90 o , 0 o , 90 o ]. Each laminate is fabricated three times, thus, 12 laminates are fabricated