Mechanical Behavior Of Natural Fiber Reinforced Composite And Its Applications

Over millions of years of evolution by natural selection,many natural fiber reinforced composites exhibit superior mechanical properties by integrating inorganic ceramics with organic molecules in a special manner.The configuration of natural fiber reinforced composites is characterized by randomly staggering of discontinuous fiber in one direction,or three-dimensional randomly distributed fibrous networks.Bio-inspired by natural fiber composites,synthetic fiber reinforced composites were developed in a bionic way.Nevertheless,with the continuous research on natural fiber composites,it has been found that the design of synthetic materials at the present stage is preliminary,and there are still many areas for improvement.Better understanding the mechanism of the deformation and stress transfer throughout natural fiber reinforced composites can help provide bioinspired clues to synthetic engineering composite material designs,decode complex physiological and pathological phenomena,and provide new insight into possible therapeutic solutions.shear lag model is originally employed to predict the stress transmission in engineering composites between fiber and matrix,whereas it need to be extendedly developed to characterized the stress rate-dependent mechanical behavior of biological natural composites due to their viscoelastic nature.Firstly,engineering composites are well-known for light-weight,high specific stiffness and strength.For the better use of composites and a deeper insight into the fracture propagation and stress transfer of fiber-matrix interface,the well-known shear lag model is applied to characterize the interfacial mechanical behavior between fiber and matrix with bilinear local bond-slip law.A parabolic shear stress is assumed to distribute along the thickness of the matrix.Theoretical expressions of the load-displacement relationship and interfacial shear stress are obtained for elastic,softening and debonding stages.Secondly,viscoelastic shear lag model needs to be developed to illustrate the micromechanical behavior between fiber and matrix in the biocomposites under dynamic loading.This paper has extended and improved the previous shear lag model by including viscoelastic behaviors for the interfibrillar matrix and related the effective stiffness of tendon and axon to the velocity of the applied load.The viscoelastic shear lag model is an essential extension to the previous shear lag models which only considered the elastic or elasto-plastic behaviors under static or quasi-static loads.Moreover,an analytical solution to Kelvin shear lag model,and numerical results for Maxwell and standard linear shear lag models have been derived.Soft matter of tendon and axon are composed of parallel arragements of collagen fibrils and microtubules,respectively,which exhibit stress rate-dependent breaking and stiffness function,owing to their viscoelastic nature.As the discontinuous fibrils and microtubules are the fundamental load-carrying elements,and interfibrillar matrix and cross-linking tau protein are responsible for large deformation,hence interfibrillar matrix and tau protein are considered as viscoelastic springs.Viscoelastic shear lag model is proposed to illustrate the micromechanical response of the tendon and axon under dynamic loading conditions.This model is developed to elucidate how the natural fiber reinforced composites protect themselves from overall damage over the course of evolution,and how the natural fiber reinforced composites simultaneously achieve a superior mechanical balance of high specific stiffness and toughness.From the perspective of material mechanics,overlap length is a significant parameter for the design strategy of engineering fiber reinforced composites.In contrast to natural biocomposites,high performance fiber reinforced composites typically use continuous fibers,thus achieving high stiffness and strength but presenting limited toughness and ductility.Bio-inspired design of the discontinuous architecture might potentially improve the toughness and ductility,and extend the applicability of fiber reinforced composites to damage tolerant structures.From the perspective of biomedical engineering,this micritubule-tau protein dynamics model can help understand the underlying pathophysiology and molecular mechanisms of diffuse axonal injury under the dynamic tensile and torsional condition.Finally,bioinspired by the three-dimensional randomly distributed fibrous networks of the extracellular matrix,palm fiber is used to manufacture mattress for beds.Notably,mechanical interaction behavior between human body and mattress is one of the crucial physical factors affecting the sleep comfort and sleep quality.In order to assess sleep(dis)comfort level without interfering with sleep lying in a supine posture,powerful tools,including three-dimensional scanning technology,finite element software,Tactilus system,MTS system and the theory of similarity measure,are employed to evaluate the quality of palm fiber mattress.On the basis of parallel aligned natural fiber reinforced composites,viscoelastic shear lag model is an essential extension to the previous shear lag models which only considered the elastic or elasto-plastic behaviors under static loads.Futhermore,we propose a novel approach to evaluate sleep comfort by using advanced technology.