Thermal residual stresses in thermoplastic CFRP-steel laminates: Modification and influence on fatigue life

2021 ◽  
pp. 1-7
Author(s):  
Joachim Hausmann ◽  
Stefan Schmidt
Keyword(s):  
Carbon Fiber ◽  
Residual Stresses ◽  
High Stress ◽  
Fatigue Loading ◽  
Internal Stresses ◽  
Material System ◽  
Fiber Reinforced ◽  
Suitable Material ◽  
Thermal Residual Stresses ◽  
Carbon Fiber Reinforced

Thermal residual stresses (TRS) in hybrid materials and structures occur by the mismatch of thermal expansion of different materials. Especially when combining metals with carbon fiber reinforced plastics (CFRP), a significant level of internal stresses can be reached. High processing temperatures and high stiffness of the constituents are also responsible for high stress levels. Laminates of thermoplastic CFRP (unidirectional carbon fiber reinforced polyamide 6) and stainless steel foils are a suitable material system to examine the TRS in detail. Since TRSs in the steel fraction are of tensile nature, these superpose to externally applied loads, resulting in higher efforts for the material and thus reduced lifetimes under cyclic fatigue loading. Therefore, a reduction of TRS is desired. Two methods for TRS reduction were applied, and its influence on fatigue lifetime was investigated. Firstly, specimens were stretched by a preloading to reduce TRS by yielding of the metal. Secondly, non-symmetric laminates were gradually cooled down after consolidation to compensate TRS formation by non-symmetric shrinkage. While preloading of materials and structures is known for TRS modification, the gradually cooling is not established, yet. Both modification principles were numerically investigated before experimental validation. A significant increase of lifetime was reached by TRS reduction.

Effect of Interfacial Nanostructure on Mode Mixity in Directly Bonded Carbon Fiber Reinforced Thermoplastic Laminates and Aluminum Alloy With Thermal Stresses

2020 ◽  
Author(s):  
Hiroki Ota ◽  
Kristine Munk Jespersen ◽  
Kei Saito ◽  
Keita Wada ◽  
Kazuki Okamoto ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Aluminum Alloy ◽  
Carbon Fiber ◽  
Residual Stresses ◽  
Adhesive Bonding ◽  
Thermal Stresses ◽  
Fiber Reinforced ◽  
Mode Mixity ◽  
Mechanical Joining ◽  
Carbon Fiber Reinforced

Abstract In recent years, for the aim of weight reduction of transportation equipment, carbon fiber reinforced thermoplastics (CFRTPs), which have high recyclability and formability, are becoming suitable for mass production. Additionally, with the development of multi-material structures, excellent technologies for joining metal and CFRTPs are required. In present industry, joining between dissimilar materials include adhesive bonding and mechanical joining methods, however, these methods still have some problems, and therefore an alternative bonding method without adhesive and mechanical joining is required for joining CFRTPs and metals. Thus, this study focused on direct bonding between CFRTP and an aluminum alloy, by producing a nanostructure on the surface of the aluminum alloy. The nanostructure penetrates the CFRTP matrix causing an anchoring effect, which results in significant bonding strength improvement. The influence of the nanostructure on the fracture toughness for the directly bonded CFRTP and aluminum was evaluated by static double cantilever beam (DCB) testing. Due to the difference of the thermal expansion coefficients between the CFRTP laminates and the aluminum alloy, significant residual stresses are generated. The effect of the thermal residual stresses on the fracture toughness along with the resulting mode mixity (mode I and II) was calculated. It is found that the thermal stresses introduce a significant mode mixity of the fracture toughness.

scholarly journals Experimental Investigation on the Creep Property of Carbon Fiber Reinforced Polymer Tendons under High Stress Levels

Materials ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 2273 ◽  
Author(s):  
Dong Yang ◽  
Jiwen Zhang ◽  
Shoutan Song ◽  
Fei Zhou ◽  
Chao Wang
Keyword(s):  
Carbon Fiber ◽  
Creep Property ◽  
High Stress ◽  
Fiber Reinforced Polymer ◽  
Carbon Fiber Reinforced Polymer ◽  
Fiber Reinforced ◽  
Creep Coefficient ◽  
Reinforced Polymer ◽  
Stress Levels ◽  
Carbon Fiber Reinforced

Carbon fiber reinforced polymer (CFRP) tendons are generally used as prestressing members to take full advantage of their high strength. Their creep property is one of the key factors influencing the reliability and safety of the structures, especially under sustained high stress. In this study, using a new wedge-type anchorage system, experimental research was carried out on the creep behavior of CFRP tendons under high stress levels from 0.69 to 0.85 fu. All the tests lasted for a duration of 1000 h. It was found that the creep coefficient tends to increase with the stress level. Compared to their static properties, the residual strength of CFRP tendons after creep tests is 4.54% lower while the after-creep elastic modulus is 6.99% higher. Through data analysis, a semi-logarithm linear relationship between the creep coefficient and time was established, and the creep coefficients at 1 million hours were extrapolated.

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