Considering geometric nonlinearity effect
Composite helical structures (CHS) have found numerous applications in engineering credit to their excellent ability to store and release elastic strain. For instance, CHS can be used as a deployable antenna to receive and transmit signals in the aerospace field. Contemporary helical structures are generally made of metal materials. The manufacturing process of metal helical structures is simple, but it does not satisfy the requirements of lightweight design due to the heavyweight. As such, replacing these metals structures with CHS can effectively reduce the weight of helical structures and take into account excellent mechanical properties. Consequently, numerous investigations have been undertaken on helical structure’s stiffness, strength, and compressive stability. There are many analytical models for calculating the compressive stiffness and compressive strength of helical structures; unfortunately, they fail to consider the change of geometric parameters of helical structures with the increase of compressive load. As such, it becomes impossible to predict the mechanical properties of helical structures within a large deformation process.
In general, it is clear that the change of geometric parameters of CHS in the deformation process almost has not been taken into account in existing theoretical investigations on mechanical behaviors of CHS. To address this, Beihang University researchers: PhD candidate Tian-Wei Liu and Professor Jiang-Bo Bai, in collaboration with Dr. Qiu-Hong Lin and Qiang Cong at the Beijing Institute of Spacecraft System Engineering, developed a new analytical model considering geometric nonlinearity for predicting the compressive behaviors (stiffness, strength, and load-displacement relationship) of CHS. Their work is currently published in the research journal, Composite Structures.
In their approach, a geometric model, in which the geometric parameters of CHS continuously changed with the increase of compressive load, was prepared. In their setup, the load-displacement relationship considering geometric nonlinearity was deduced by using the energy principle and accumulative compressive load increment and accumulative deformation increment. Subsequently, the compressive stiffness of CHS was obtained using a linear fitting with the least square method. The analytical expression of compressive strength of CHS was derived from the Tsai‐hill criterion and the principal stresses.
The authors reported that the predicted results using the new analytical model correlated well with the experimental data, especially for CHS with a large helix angle, and it had better prediction accuracy and a wider application range. In addition, the obtained results showed that the geometric nonlinearity effect should be considered in the theoretical prediction or numerical simulation of the compressive behavior of CHS, which may help improve the prediction accuracy.
In summary, the study proposed an analytical model for predicting the compressive behavior of CHS considering the geometric nonlinearity effect. In this work, the load-displacement relationship considering geometric nonlinearity was deduced by using the energy principle and accumulative compressive load increment and accumulative deformation increment. In a statement to Advances in Engineering, Professor Jiang-Bo Bai explained that the analytical model considering geometric nonlinearity effect proposed was practical and convenient since only a few geometric parameters and mechanical properties of constituent materials are required to predict compressive behavior of CHS with arbitrary helix angle, which has a good practical value in engineering.
Tian-Wei Liu, Jiang-Bo Bai, Qiu-Hong Lin, Qiang Cong. An analytical model for predicting compressive behavior of composite helical Structures: Considering geometric nonlinearity effect. Composite Structures 255 (2021) 112908.