以導電性監測複材膠合接口濕熱老化破壞之探討

Abstract

膠合接口在複合材料結構中廣泛應用，與傳統連接方法相比有許多優點。然而，濕熱環境會導致搭接劑和複合材料性能劣化，使其連接機械性能變得不可預測。傳統非破壞檢驗技術（NDT）難以檢測出明顯缺陷形成前的膠合接口破壞情況。透過結構健康監測（SHM），可以監測試片在機械負載和環境影響下的劣化程度。 本研究將奈米碳管（CNT）摻入環氧樹脂搭接劑中，使碳纖維複合材料膠合接口具備導電性。為瞭解試片在正常乾燥環境中的疲勞破壞情況，設定在達到特定電壓變化百分比（2%、10%、18%）時進行螢光液滲透處理，以探討疲勞壽命、電壓變化百分比及破斷面破壞機制之間的關聯性。接著，對試片在濕熱環境中進行 30天和90 天的測試，並同時進行導電性監測，探討不同濕熱環境下的機械性質與監測電壓之間的相關性。最後，通過對破斷面的微觀觀察和監測數據的分析，探討電性與破壞之間的關聯性。 實驗結果顯示，電壓變化百分比與液滲脫層面積之間存在兩種趨勢，並通過微觀觀察揭示了這兩種趨勢的破壞機制。此外，在濕熱環境中的電壓監測結果顯示，電壓值隨時間增加，且與疲勞壽命有一定關聯性。高溫高濕條件下，複合材料基材和搭接劑均出現塑化現象，並存在由水分侵入引起的孔洞。 總體來說，本研究揭示了濕熱環境對複合材料結構的影響，並指出導電性監測與機械性質之間的關聯。這對理解複合材料在特定環境條件下的性能變化至關重要。然而，仍需進一步研究以解釋濕熱老化、導電性和機械性質之間的複雜關係，以提高對複合材料結構性能的預測和控制。

Adhesive joints are widely used in composite material structures and offer many advantages compared to traditional connection methods. However, hygrothermal environments can degrade the performance of the adhesive and composite materials, making the mechanical properties of the joints unpredictable. Traditional non-destructive testing (NDT) techniques have difficulty detecting adhesive joint failures before significant defects form. Structural health monitoring (SHM) can monitor the degradation of specimens under mechanical loads and environmental impacts. This study incorporates carbon nanotubes (CNTs) into epoxy adhesives to create conductive adhesive joints in carbon fiber composites. To understand the failure behavior of the specimens under fatigue loads in dry environment, the study used liquid fluorescent penetrant treatment at specific voltage change percentages (2%, 10%, 18%) to explore the relationship between fatigue life, voltage change percentage, and failure mechanisms of the fracture surface. Subsequently, the specimens were tested in hygrothermal environments for 30 and 90 days while monitoring conductivity to investigate the correlation between mechanical properties and monitored voltage under different environmental conditions. Finally, microscopic observations of the fracture surfaces and analysis of the electrical trends during monitoring were conducted to explore the relationship between electrical properties and failure. The experimental results show two trends between the voltage change percentage and the area of liquid penetration delamination, and microscopic observations revealed the failure mechanisms for these trends. Additionally, voltage monitoring in the hygrothermal environment showed that voltage values increased over time and correlated with fatigue life. Further microscopic observations indicated that both the composite material substrate and the adhesive exhibited plasticization under high temperature and humidity conditions, and pores caused by moisture intrusion were present. Overall, this study reveals the impact of hygrothermal environments on composite material structures and highlights the differences between conductivity monitoring and mechanical properties. This is crucial for understanding the performance changes of composite materials under specific environmental conditions. However, further research is needed to explain the complex relationships between hygrothermal aging, conductivity, and mechanical properties to improve the prediction and control of composite material structural performance.