Abstract
For achieving high quality of in situ consolidation in thermoplastic Automated Fiber Placement, an approach is presented in this research work. The approach deals with the combination of material pre-heating and sub-ultrasonic vibration treatment. Therefore, this research work investigates the influence of frequency dependent consolidation pressure on the consolidation quality. A simplified experimental setup was developed that uses resistance electrical heating instead of the laser to establish the thermal consolidation condition in a universal testing machine. Consolidation experiments with frequencies up to 1 kHz were conducted. The manufactured specimens are examined using laser scanning microscopy to evaluate the bonding interface and differential scanning calorimetry to evaluate the degree of crystallinity. Additionally, the vibration-assisted specimens were compared to specimens manufactured with static consolidation pressure only. As a result of the experimental study, the interlaminar pore fraction and degree of compaction show a positive dependency to higher frequencies. The porosity decreases from 0.60% to 0.13% while the degree of compaction increases from 8.64% to 12.49% when increasing the vibration frequency up to 1 kHz. The differential scanning calorimetry experiments show that the crystallinity of the matrix is not affected by vibration-assisted consolidation.
Highlights
Thermoplastic fiber-reinforced composites (TPC) are attracting increasing interest in the aviation industry due to their advantages, such as weldability, recyclability, chemical resistance and fracture toughness compared to thermoset materials [1,2,3]
The porosity decreases from 0.60% to 0.13% while the degree of compaction increases from 8.64% to 12.49% when increasing the vibration frequency up to 1 kHz
With regard to the relaxation kinetics of the neat thermoplastic matrix material that are related to the viscosity of the matrix material and the consolidation force, the evaluation of the change in consolidation force was conducted to evaluate a change in viscosity
Summary
Thermoplastic fiber-reinforced composites (TPC) are attracting increasing interest in the aviation industry due to their advantages, such as weldability, recyclability, chemical resistance and fracture toughness compared to thermoset materials [1,2,3]. The frequency-dependent shear-thinning effect of the viscoelastic matrix material will be used to decrease the viscosity within the consolidation as well as dissipative heat generation which is known from tape winding [30,31,32] and ultrasonic welding [33,34,35] of the thermoplastic material will be used to compensate the temperature loss and avoid overheating Both the shear-thinning effect and dissipative heat effect shall have a positive effect on the development of intimate contact and on the resulting consolidation quality. 3due of 12 to the high temperature deconsolidation effects, e.g., void growth as a consequence of temperature-dependent gas expansion, are observable [29]
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