In‐line residual strain monitoring for thermoplastic automated tape layup using fiber Bragg grating sensors

Abstract

Automated tape layup (ATL) has been used extensively for manufacturing composites laminates using unidirectional prepregs for high‐performance industries like aerospace. Residual stress is one of the defects that adversely affect the layup quality. These stresses affect geometrical tolerances in the form of distortion of the final product and are found to have a detrimental impact on the mechanical properties. In‐line monitoring of such defects will help in productivity increase and achieving a reliable process control. The aim of the present work is to demonstrate the feasibility of fiber Bragg grating sensors for monitoring residual strains. FBGs are embedded inside a thermoplastic UD laminate. Temperature and strain discrimination is performed to recognize intermittent residual strains during the layup. Finally, intermittent residual strain is used to develop an understanding of the global residual strain. Effect of selective process parameter on residual stress formation and the evolution of the same is also analyzed.

Effect of embedded periodic fiber placement gap defects on the microstructure and bistable behavior of thermoplastic composite laminates

“…This is primarily because the 0 layer bends along the fiber direction at the first stable state, and the embedding of the gaps reduces stiffness along the bending direction, resulting in an increase in curvature, as shown in Figure 5B. The opposite trend is observed for the second stable state, and the corresponding theory can be derived from the investigation of Kumar et al 24 The maximum errors of maximum out-of-plane displacements in the first stable states are 11.17%, whereas the maximum errors of maximum out-of-plane displacements in the second stable states are 9.74%. The maximum out-of-plane displacements obtained from the experiments are all smaller than those obtained from the finite element model, mainly because the finite element method uses simplified linear edges instead of wavy edges of gaps, thus underestimating the effect of wavy edges of gaps on the curvature of the laminates.…”

“…Conventional hand lay-up techniques are severely constrained owing to the low productivity and inaccuracies of manual operations. 23,24 Automated tape laying (ATL) and automated fiber placement (AFP) have been developed to enhance productivity in addition to the size of structures. 25 ATL is capable of laying wide unidirectional prepreg tapes on sample molds, while AFP utilizes a bunch of narrow tows of fiber prepreg material and places them adjacent to each other during the fabrication process.…”

“…As a typical deployable component, the automation of the production process for large‐sized bistable structures is imminent. Conventional hand lay‐up techniques are severely constrained owing to the low productivity and inaccuracies of manual operations 23,24 . Automated tape laying (ATL) and automated fiber placement (AFP) have been developed to enhance productivity in addition to the size of structures 25 .…”

Monitoring and verification of micro‐strain generated inside the laminate subjected to thermal loading through fiber bragg grating sensors and classical laminate theory

“…The glass fiber was simultaneously used as a reinforcing agent and a sensor to monitor the residual stresses in a single fiber composite. Yadav et al [ 14 ] studied the effectiveness of fiber Bragg grating sensors for monitoring residual strains for carbon fiber‐reinforced thermoplastic automated tape layup. A cure monitoring system is designed using the FBG sensor to find the best curing cycle, which results in the least amount of residual thermal stress in CFRP materials.…”

Analysis and characterization of interlaminar tack for different prepreg materials during automated fiber placement

“…Recently, automated tape placement (ATP) and AFP have been used in the aerospace industry widely as a more efficient and productive manufacturing method for composite materials. [1][2][3] During AFP, the adhesion level (tack) between the applied prepreg and the surface of the mold or between the adjacent layers of the prepreg is one of the crucial properties that dominate the placement quality. [4,5] If the interlaminar stress between prepreg and substrate exceeds the tackiness, [6,7] defects such as gaps, out-of-plane wrinkles, or tow pull-up would occur during AFP, as schematically illustrated in Figure 1.…”