Xianghe Peng

Research on the microstructure of insect cuticle and the strength of a biomimetic preformed hole composite.

The insect cuticle is a typical natural composite with excellent strength, stiffness, and fracture toughness. Scanning electron microscope observation of the microstructure of Hydrophilidae (an insect) cuticle showed several unique plies and structural characteristics, which may provide available information to the design of advanced composites. The microstructure found in the vicinity of pore canals in the insect cuticle was used for the design of the composite laminate with a hole. Compared with the composite laminate with a normally drilled hole, it was found that the strength of the specially designed composite laminate increases markedly, which is of important significance to the design of high-performance composites.

Hydroxyapatite-Sheet Parallel Microstructure of Shinbone

Bone is a natural biomaterial. It behaves favorable strength, stiffness and fracture toughness, which are closely related to its eximious microstructure. Scanning Electron Microscope (SEM) observation on a shinbone showed that the bone is a bioceramic composite consisting of laminated hydroxyapatite and collagen matrix. The hydroxyapatite layers are parallel with the surface of the bone and consist of long and thin hydroxyapatite sheets. The observation also showed that the hydroxyapatite sheets in different hydroxyapatite layers also parallel with each other, which composes a hydroxyapatite-sheet parallel microstructure. The maximum pullout energy of the parallel microstructure was investigated based on its representative model. It was shown that the long and thin shape of the hydroxyapatite sheets in the parallel microstructure is profitable to increase the maximum pullout energy and enhance the fracture toughness of the bone.

RESEARCH ON THE NANOMETER DENDRITIC FIBERS IN DORBEETLE CUTICLE

The SEM observation on the cuticle of dorbeetle shows that the cuticle is composed of chitin fibers and protein matrix. The diameter of chitin fibers is from several to several-hundred nanometers. The observation also shows that there is a kind of dendritic fiber in the cuticle. The maximum pullout force of the dendritic fiber is analyzed based on its representative model. The analysis shows that the dendritic fibers can markedly increase the pullout force of the fibers and improve the fracture toughness of the cuticle.

Investigation to nano corkscrew structure in Lucanidae cuticle

The microstructure of a Lucanidae cuticle was observed with a scanning electronic microscope (SEM). It was found that the insect cuticle is a kind of biocomposite consisting of nanometer chitin fibers and sclerotic-protein matrix. There is a kind of corkscrew nano-chitin-fiber structure in the cuticle, in which the fibers in different layers have different orientations, which may improve the fracture toughness of the cuticle. The maximum pullout force of the corkscrew nano-chitin-fiber structure was analyzed and compared with that of the conventional parallel-fiber structure based on their representative volume element. It showed that the maximum pullout force of the corkscrew nano-chitin-fiber structure is markedly larger than that of the conventional parallel-fiber structure. A comparative experiment on the maximum pullout forces of the corkscrew-fiber and the parallel-fiber structures was conducted. Comparison shows that the analytical results agree well with the experimental results.

Constitutive Model for Casting Magnesium Alloy Involving Spherical Void Evolution

Casting magnesium alloys are highly heterogeneous materials inevitably containing numerous voids. These voids will evolve during material deformation and markedly affect material behaviors, so it is important to investigate the equation of the void evolution and the constitutive relation involving the void evolution. By assuming the voids in casting magnesium alloys were spherical, the growth equation of the voids was obtained from the incompressibility and continuity conditions of material matrix. Through combining the obtained void-growth equation with the void-nucleation equation relative to the increment of intrinsic-time measure, the evolution equation of the voids was presented. By introducing the presented void-evolution equation to a nonclassical elastoplastic constitutive equation, a constitutive model involving the void evolution was put forward. The corresponding numerical algorithm and finite element procedure of the model were developed and applied to the analysis of the elastoplastic response and the porosity change of casting magnesium alloy ZL305. Computed results show satisfactory agreement with those of the corresponding experiments.

Inelastic simulation of insect cuticle using artificial neural network

Neural networks have been availably applied to the simulations of the mechanical behaviors of many materials. In this work, a neural network material model is built for the simulation of the inelastic behavior of biocomposite insect cuticle. Radial basis function neural network is adopted in the simulation for that the neural network has the characteristic of fast and exactly completing the simulation. In the construction of the neural network, the network is trained based on the experimental data of the load-displacement relationship of a chafer cuticle. A strain-controlled mode and the iterative method of data are adopted in the training process of the neural network. The obtained neural network model is used for the simulation of the inelastic behavior of another kind of insect cuticle. It is shown that the obtained material model of the radial basis function neural network can satisfactorily simulate the inelastic behavior of insect cuticle.

RESEARCH OF THE NANOMETER HELICOIDAL LAYUP OF RUFESCENS SHELL

A scanning electron microscope (SEM) observation on a Rufescens shell shows that the shell is a bio-ceramic composite consisting of aragonite sheets with nanometer scale and organic matrix. These nano-aragonite sheets are arranged in the shell in the form of helicoidal layup. The reason of the excellent fracture toughness of the shell is analyzed based on the maximal pullout force of the helicoidal layup of the aragonite sheets in the shell.

Microscopically based new damage constitutive model with applications

In this paper we put forward a new formulation of constitutive relations based on micro-mechanical analysis to describe the behavior of damaged materials. The constitutive theory of continuum damage mechanics has been further developed, based on the foundations of elastoplastic deformation and analysis of the mechanical behavior of a microelement of damaged material in which different damage mechanisms are involved. The description of ductile fracture phenomena by the evolution of damage parameter f, measuring the void volume fraction, is applied. Softening functions have been introduced into the macroscopic constitutive equations to model the damage effects on material response. The method has been applied to the analysis of the stress and damage distribution near the tip of the notch of the notched bar under uniaxial loading. Calculated results for distribution of stress and damage, based on the new constitutive description and corresponding finite element code, are compared with the experimental data obtained by deformation tests and photointerpreter. Calculated results show satisfactory agreement with experimental data.