Metallic sandwich plates with various inner cores have important new structures with not only ultra-light material characteristics and load bearing function but also multifunctional potential including good energy absorbers during impact loading, thermal isolation opportunities, good sound dampers, heat exchangers, current collectors. Because of production on the large scale and a good geometric precision, sandwich plates with inner dimpled shell structure from a single material have a benefit as compared with other competitive sandwich plates. Inner dimpled shell structures can be fabricated with press or roll forming process, and then bonded with two face sheets by multi-point resistance welding or adhesive bonding.
Due to good formability as confirmed from FE analysis, dimpled shell structures are found to be stiffer and more flexible than other shapes such as cone, cup, egg-box shapes. Metallic sandwich plates with inner dimpled shell structure can be optimally designed for minimum weight subject to prescribed combination of bending and transverse shear loads. Fundamental findings for lightweight design are presented by restricted optimization. Failure responses of sandwich plates are predicted and formulated with an assumption of narrow sandwich beam theory. Failure is attributed to four kinds of mechanisms: face yielding, face buckling, dimple buckling and dimple collapse. Failure mode boundaries and same strength lines dependent upon the geometry and yield strain of the material are plotted with respect to geometric parameters on the failure map. Because optimal parameters of maximum strength for given material weight can be selected from the map, Analytic solutions for maximum strength are expressed as a function of only material property and proposed strength. These optimal parameters match well with numerical optimal parameters.
Efficient finite element method has been introduced for metallic sandwich plates subject to 3-point bending. A full model 3-point bending FE-analysis shows that the plastic behavior of inner structures appears only at the load point. The unit structures of sandwich plates are defined to numerically calculate the bending stiffness and strength utilizing the recurrent boundary condition for pure bending analysis. The equivalent models with same bending stiffness and strength of full models are then designed analytically. It is demonstrated that the results of both models are almost the same and the FE-analysis method incorporating equivalent models can reduce the computation time effectively.
Elasto-plastic bending behavior of sandwich plates have been predicted analytically, measured and simulated. The simulations have shown that Elastic perfectly plastic approximation and FE-analysis incorporating equivalent models can be conveniently employed with less than 10% error in elastic stiffness, collapse load, and energy absorption. The dominant collapse modes are face buckling and bonding failure after yielding. Since the inner dimpled structures prevent face buckling, sandwich plates with inner dimpled shell structure can absorb more energy than other types of sandwich plates during the bending behavior.
금속 샌드위치 판재는 다양한 형태의 내부구조를 가지는 새로운 구조로써 초경량, 고강도, 고강성의 특성 외에 충격에너지 흡수, 단열, 방음, 열교환 등의 고기능성 판재로써의 가능성을 가지고 있다. 대량생산성과 정밀도측면에서 딤플형 내부구조 금속 샌드위치 판재는 다른 내부구조 금속 샌드위치 판재보다 장점을 가지고 있으며 다점 저항용접이나 접착제 접합을 통해 표면판재와 접합되어 제작될 수 있다. 유한요소 해석 결과, 내부구조를 재작할 때 딤플형 내부구조가 컵, 콘, 달걀박스형 내부구조보다는 성형성이 좋아 굽힘 강성을 개선 할 수 있으며 여러 구속 조건에 의해 굽힘 하중에 대하여 최적화되었다. 좁은 빔이론과 SQP-PD 알고리즘으로 최적화하면 표면판재항복, 표면판재좌굴, 내부딤플파손의 경계에서 최적의 설계변수가 존재하며 반구형 딤플이 최적의 내부구조형상이다. 이 결과로부터 파손선도를 작성하고 등강도 선도를 도시하며 최대강도를 가지는 변수조합을 찾을 수 있고 최적의 설계변수를 물성과 목표 강도의 함수로 표기할 수 있다. 굽힘 하중을 받는 샌드위치 판재의 굽힘 거동을 효율적으로 예측하기 위하여 등가형상을 이용한 해석기법을 제안하였으며 그 결과를 이론과 실험의 결과와 비교해보면 10%의 오차범위 내에서 굽힘강성, 강도, 붕괴하중, 에너지 흡수량등을 예측할 수 있었으며 등가형상을 이용하여 붕괴모드와 굽힘 거동을 효율적으로 예측할 수 있다는 것을 알았다. 그리고, 딤플형 내부구조 샌드위치 판재는 붕괴 후 하중을 유지하는 특성을 가지고 있어 유사 샌드위치 판재보다 많 에너지를 흡수할 수 있다.
