Tan Huifeng

Shaping of Rollable, Singly Curved, Parabolic Shell Reflectors

A novel, rollable, singly curved, parabolic shell reflector and its nontrivial shaping method were developed. The rollable shell reflector was a monolithic thin rectangular plate with linearly varying thickness, and it was able to roll up elastically around a mandrel. A system of end moments and loads was used to shape the linearly thickness-tapered plate into a parabolic cylinder, and a mathematical model was deduced to predict the shape accuracy of the thin plate based on nonlinear beam theory. A certain parabolic cylinder reflector was analyzed by the proposed shaping method. The optimized shape accuracy agreed well with the simulation result, and it was able to meet the precision requirement. The proposed shaping method provided a promising technology for enabling a high-precision parabolic cylinder shell reflector with different apertures.

Membrane Buckling Patterns and Secondary Buckling Analysis

In this paper, the shear wrinkles of a rectangular membrane under the pretension were analyzed firstly. A critical shear distance was then obtained based on the tension field theory. An expression between the wavelength and the amplitude of the membrane wrinkles were developed using the Von Karman large deflection formula. The simulation flow of the membrane wrinkles were also established using the nonlinear post-buckling analytical method. The results indicated that the wrinkle was firstly generated on both sides of the membrane and then extended to the center. The wrinkle amplitude increased with the shear distance increases. The wrinkle formation and expansion were effectively resisted by increasing the initial pretension. Buckling mode of the shear membrane was unstable in the post-buckling process and the secondary buckling phenomenon was obviously observed. The theoretical and numerical results were compared to verify the rationality of the theoretical and simulation results.

Method of model analysis for flexible head impacting with elastic plane

To consider the head is a flexible multi-layer structure and the contact-impact is flexible, the Hertz Contact Law is unsuitable for analyzing the dynamic response of human head impacts elastic plane with initial speed. In this paper, the process of head impacting with elastic plane is modeled as a response of vibrant system, and methods like mechanical network figure and mechanical impedance is taken to resolve this dynamic response problem. Based on the actual head structure, head is modeled as a vibrant model, which concludes the masses of scalp and bone in the impact area, the masses in the other part of the head and the brain, the stiffness of the head, and the damp coefficient of the scalp and brain. At the same time, the elastic plane is simplified as a vibrant model including mass, stiffness and damp. These two vibrant models are linked into one vibrant systematic model. In order to calculate the elastic deformation and the impact acceleration of the head, the models are transformed into mechanical girding figure at violent vibration point. The dynamic impact force of the system, the impact acceleration of the head, the elastic deformation of the plane and the fixed frequency of the system can be worked out by calculating the velocity impedance at the violent vibration point when the initial impact speed is known. The results fit the test data well, which proves that this method is available for the analysis of the dynamic response of the system under impact.

Bias tensile properties and cycle performance of aluminum coated aramid fabric for the aerostatics envelope

The aluminum coated aramid fabric is a potential envelope material for aerostatics duo to its excellent mechanical properties. Monotonous and cyclic tensile loading experiments are conducted here to investigate the mechanical behaviors of the fabric. The off-axial tensile tests are carried out initially to study the nonlinear behaviors and the anisotropic properties. Then, cycle tensile tests with different stress amplitude are conducted to study the inelastic behaviors both in warp and weft directions. Results show that the bias angle affects the tensile behaviors significantly. Both residual strains and tangent modulus increase along with the increasing of cycle numbers. The stress amplitude is another important factor in influencing the residual strain and modulus of the coated fabric.

Mechanical Parameters Determination of a Polymeric Membrane by Digital Image Correlation

Digital image correlation (DIC) is a powerful method for full-field strain test of polymeric materials and speckle pattern on the materials surface is a critical factor for the measurement accuracy. In this paper, a new speckle pattern technique is presented and used on mechanical parameter determination of a thin and soft polymeric membrane. The presented speckle pattern is generated by combination of image noise technology and film printing technique, and it is much easier to get fine speckle pattern compared with traditional spray speckle pattern technique which is a hard and time-cost work. To verify the validity of the presented speckle pattern technique, Youngs modulus and Poissons ratio are measured by presented speckle pattern and spray speckle pattern on a tensile testing machine. It is found that the measurement results by presented speckle pattern agree well with that by fine spray speckle pattern. With the presented speckle pattern technique, DIC becomes a more convenient and fast non-contact measurement technology for polymeric materials test.