Investigation of non-uniform gelation effects on residual stresses of thick laminates based on tailed FBG sensor

Abstract

Due to the appearance of temperature gradient and non-uniform gelation, fully understanding of residual stresses is even more complex in thick laminates. In this paper, basic mechanisms of cure process were presented firstly. Then, experimental investigation of the non-uniform gelation was carried out together with characterization of necessary material properties. Tailed FBG sets were applied to monitor the cure of thick laminates with temperature gradient. The non-uniform gelation and chemical shrinkage gradient were captured successfully. Lastly, FEM analysis integrating thermal-chemical sub-model and stress-displacement sub-model was carried out to reveal the development of residual stresses. It is demonstrated that the high temperature layer gelled earlier and showed more chemical shrinkage. The chemical strain gradient would introduce compression internal stresses in prior gelled layer and introduces tensile internal stresses in later gelled layer. For the case studied here, transverse residual stress generated by non-uniform chemical shrinkage is small. The strategy used here is promising to estimate the residual stresses for more complex cases further.

Residual stress in fiber reinforced thermosetting composites: A review of measurement techniques

“…The use of embedded fiber optic sensors in laminates is still very prevalent with many examples of this technique being successfully applied to the monitoring of internal strains during cure in thermosets [ 102–105 ] and thermoplastics [ 57, 106, 107 ] where a higher operating temperature is required. Another key benefit of fiber optic sensors is that they can often be repurposed after cure as condition monitoring devices.…”

Cure-induced residual stresses for warpage reduction in thermoset laminates

“…Cure induced residual stresses arise within the part due to thermal expansion anisotropy, resin shrinkage and tool-part interaction. [1][2][3][4] The influence of the cureinduced residual stresses on the manufactured part is twofold. On one hand, experimental studies have shown the influence of residual stresses upon mechanical performances of the final part could be beneficial with respect to longitudinal and transverse tensile strength [5][6][7] and delamination properties 8,9 and detrimental in the case of in-plane shear strength.…”

Measurement of manufacture assembly stresses in thick composite components using a modified DHD method

“…Although carbon fiber reinforced plastic (CFRP) are widely used in new generation airframe structures such as for the Airbus A350XWB and Boeing 787, it is still difficult to manufacture precisely large-scale CFRP structures and ensure their structural integrity during operation. Due to thermalchemical-mechanical interactions, thermal expansion mismatch, chemical cure shrinkage and toolparts interactions during the manufacturing process, composite components tend to deviate more from their designed geometrical configuration than metallic ones [1][2][3][4]. Counteracting these undesired manufacturing distortions and geometric deviations for composite structures is still a challenge for manufacturers.…”