Evaluation of Fatigue Crack Propagation Characteristics under Different Fracture Modes in CFRP Bonded Joints with Urethane Adhesive

Toshiharu Hama･Masayuki Osada (Hiroshima Univ)･Toshiaki Nakamaru (Nissan Motor Co. , Ltd)･Yuki Ogawa･Hiroyuki Akebono･Atsushi Sugeta (Hiroshima Univ)

To achieve CN, the application of lightweight materials such as CFRP is expanding in automotive body structures. Adhesive bonding, which enables joining dissimilar materials, is also gaining attention, necessitating the establishment of CFRP bonded structure and its fatigue charactreristic. In this study, to establish fatigue design guidelines for CFRP bonded joints with a urethane adhesive, fatigue crack propagation characteristics for different fracture modes were elucidated.

Evaluation method of crack propagation life of CFRP bonded structures using urethane adhesives

Takuya Yuasa (Nissan Motor)･Noriyuki Kawai (Mazda)･Takamitsu Nishiya (Isuzu Motors)･Hiroyuki Sato (PRESS KOGYO)･Yoshiki Yokote (Hino Motors)･Kousuke Satou･Toshiaki Nakamaru (Nissan Motor)･Takeshi Ogawa (Aoyama Gakuin University)

Crack growth behavior of CFRP adhesive bonded structures, in which most of the whole life is occupied by crack growth of urethane adhesive, was clarified by experimental measurement and finite element analysis of hat shaped torsional specimens simulating actual car body structure. In addition, the fracture mechanics analysis was conducted, and verified the evaluation criteria by comparing with lap shear specimens and I-shaped bending specimens.

Development of an Evaluation Method for Component Performance Considering Material Property Variations in Aluminum Die-Cast Parts Using Machine Learning

Yuki Okumoto･Kyosuke Hamaishi･Takahiro Izawa･Ichiro Kono･Taichi Hirakawa･Hiromasa Honji･Nobuyuki Oda･Manabu Tatsuda･Kosuke Kojima･Ryo Yamamoto (Mazda)

In recent years, the application of high-pressure die-cast aluminum (HPDC) to vehicle body structures has expanded. Since material variations occur during the manufacturing process, it is essential to determine specifications with sufficient consideration of their impact on vehicle performance. In this study, we developed a CAE methodology that predicts material properties for each component using machine learning and integrates these predictions with crash analysis.

Fatigue Evaluation and Rapid Fatigue Strength Determination of C-SMC Using Thermoelastic Temperature Variations

Atsushi Akai (Kyoto University of Education)･Yukihiro Hamada (Toyota Motor)･Yasumoto Sato (Toyota Central R&D Labs.)･Atsushi Mikuni (Toyota Motor)

Recently, carbon fiber sheet molding compound (C-SMC), which is a discontinuous carbon fiber-reinforced polymer composite fabricated via sheet molding compound methods, has attracted increasing interest in the automotive industry. Knowing the fatigue strength of a material is indispensable for structural design; however, its determination is time-consuming and costly. In this study, fatigue evaluation and rapid determination of fatigue strength using thermoelastic temperature variations are performed on C-SMC.

Analysis of Fatigue Durability Testing and Innovative Improvement for Glass Fiber Reinforced Plastic (GFRP) Leaf Springs

SOO-SIK CHUNG (Hyundai Motor)

To enhance vehicle lightweighting and space efficiency, Glass Fiber Reinforced Plastic (GFRP) leaf springs were developed to replace metal coil springs. This study evaluated the durability of pre-developed GFRP leaf springs and their real-world applicability. A fixture replicating vehicle assembly conditions was used for durability tests under room temperature and high-temperature/high-humidity (70°C, 75% humidity). Initial prototypes showed cracks and delamination; improved versions doubled durability. Environmental tests indicated reduced durability in harsh conditions. Results validate GFRP leaf springs' durability and suggest further design optimization and testing to expand automotive applications.

Development of Open Top Air Body Structure Using Hot Blow Method

Do Hoi KIM･Kang Chul Lee (Hyundai Motor)･Golam Ahmed･Eddings Forrest･Dhananjay More･Vinaya Kumar Rachala (Hyundai America Technical Center Incorporation)

This study develops an Open Air Top vehicle body using hot blow forming, enabling detachable roofs with improved rigidity and safety. Two designs were evaluated: a Close Type with integrated high-strength pipes and an Open Type featuring exposed pipes for enhanced openness. Structural and collision analyses showed that despite reduced roof rail cross-sections and absence of the roof panel, up to 60% of base body stiffness was achieved, with reinforcements improving collision performance. Manufacturing feasibility was confirmed through prototype development. This research establishes hot blow forming as a lightweight, strong, and modular approach that meets consumer and safety demands.