J Mater Sci(2008)43:6747-6757 DOI10.1007/10853-008-26920 STRETCHING THE ENDURANCE BOUNDARY OF COMPOSITE MATERIALS: PUSHING THE PERFORMANCE LIMIT OF COMPOSITE STRUCTURES Review of the role of the interphase in the control of composite performance on micro-and nano-length scales J.Jancar Received: 3 April 2008/ Accepted: 30 April 2008/ Published online: 16 August 2008 e Springer Science+Business Media, LLC 2008 Abstract In fiber reinforced composites(FRCs), exhib- re-define term interphase on the nano-scale. Thus, the iting heterogeneous structure at multiple length scales, the Rubinstein reptation model and a simple percolation model interphase phenomena at various length scales were shown were used to describe immobilization of chains near solid to be of pivotal importance for the control of the perfor- nano-particles and to explain the peculiarities in the vis- mance and reliability of such structures. Various models coleastic response of nano-scale"interphase. " It has also based on continuum mechanics were used to describe been shown that below 5 nm. Bernoulli-Euler mechanical response of laminates and large FRC parts, along with the proposed reptation dynamics approach, 3L effects of the macro- and meso-scale interphase on the elasticity becomes not valid and higher-order elasticity satisfactorily. At the micro-scale, the interphase is con- provide suitable means for bridging the gap in modeling sidered a 3D continuum with ascribed average properties. the transition between the mechanics of continuum matter Number of continuum mechanics models was derived over at the micro-scale and mechanics of discrete matter at the the last 50 years to describe the stress transfer between nano-scale. matrix and individual fiber with realtively good success In these models, the interphase was characterized by some average shear strength, ta, and elastic modulus, En. On the other hand, models for tranforming the properties of the Introduction micro-scale interphase around individual fiber into the mechanical response of macroscopic multifiber composite Continuum mechanics can be used to describe effects of have not been generally successfull. The anisotropy of micro-scale interphase on the stress transfer in single fiber these composite structures are the main reasons causing the composites considering the system a three phase material failure of these models. The strong thickness dependence in which the individual phases, i.e., solid inclusion, matrix of the elastic modulus of the micro-scale interphase sug- and interphase, can be characterized by some average gested the presence of its underlying sub-structure. On the properties [1-5]. Unlike at the micro-scale, extreme cau- nano-scale, the discrete molecular structure of the polymer tion has to be exercised when selecting suitable modelin has to be considered. The term interphase, originally scheme at the nano-scale when the discrete molecular roduced for continuum matter, has to be re-defined to structure of the polymer becomes obvious. One of the main include the discrete nature of the matter at this length scale. difficulties when considering nano-scale in composites is to The segmental immobilization resulting in retarded repta- determine the size of the representative volume in which tion of chains caused by interactions with solid surface the discrete nature of the composite structure has to be seems to be the primary phenomenon which can be used to taken into account [6]. Very little has been written so far on the laws governing the transition between the nano-and J. Jancar(凶 micro-length scales, especially, on the reliability of clas Institute of Materials Chemistry, Brno University of Technology, sical continuum mechanics when scaled outside their Brno, Czech Republic validity range, i.e., down to the nano-scale [7]. Thus, it e-mail: jancar@fch. vutbr cz seems desirable to perform a critical review of the current 2 SpringerSTRETCHING THE ENDURANCE BOUNDARY OF COMPOSITE MATERIALS: PUSHING THE PERFORMANCE LIMIT OF COMPOSITE STRUCTURES Review of the role of the interphase in the control of composite performance on micro- and nano-length scales J. Jancar Received: 3 April 2008 / Accepted: 30 April 2008 / Published online: 16 August 2008
Springer Science+Business Media, LLC 2008 Abstract In fiber reinforced composites (FRCs), exhib￾iting heterogeneous structure at multiple length scales, the interphase phenomena at various length scales were shown to be of pivotal importance for the control of the perfor￾mance and reliability of such structures. Various models based on continuum mechanics were used to describe effects of the macro- and meso-scale interphase on the mechanical response of laminates and large FRC parts, satisfactorilly. At the micro-scale, the interphase is con￾sidered a 3D continuum with ascribed average properties. Number of continuum mechanics models was derived over the last 50 years to describe the stress transfer between matrix and individual fiber with realtively good success. In these models, the interphase was characterized by some average shear strength, sa, and elastic modulus, Ea. On the other hand, models for tranforming the properties of the micro-scale interphase around individual fiber into the mechanical response of macroscopic multifiber composite have not been generally successfull. The anisotropy of these composite structures are the main reasons causing the failure of these models. The strong thickness dependence of the elastic modulus of the micro-scale interphase sug￾gested the presence of its underlying sub-structure. On the nano-scale, the discrete molecular structure of the polymer has to be considered. The term interphase, originally introduced for continuum matter, has to be re-defined to include the discrete nature of the matter at this length scale. The segmental immobilization resulting in retarded repta￾tion of chains caused by interactions with solid surface seems to be the primary phenomenon which can be used to re-define term interphase on the nano-scale. Thus, the Rubinstein reptation model and a simple percolation model were used to describe immobilization of chains near solid nano-particles and to explain the peculiarities in the vis￾coleastic response of nano-scale ‘‘interphase.’’ It has also been shown that below 5 nm, Bernoulli–Euler continuum elasticity becomes not valid and higher-order elasticity along with the proposed reptation dynamics approach can provide suitable means for bridging the gap in modeling the transition between the mechanics of continuum matter at the micro-scale and mechanics of discrete matter at the nano-scale. Introduction Continuum mechanics can be used to describe effects of micro-scale interphase on the stress transfer in single fiber composites considering the system a three phase material in which the individual phases, i.e., solid inclusion, matrix and interphase, can be characterized by some average properties [1–5]. Unlike at the micro-scale, extreme cau￾tion has to be exercised when selecting suitable modeling scheme at the nano-scale when the discrete molecular structure of the polymer becomes obvious. One of the main difficulties when considering nano-scale in composites is to determine the size of the representative volume in which the discrete nature of the composite structure has to be taken into account [6]. Very little has been written so far on the laws governing the transition between the nano- and micro-length scales, especially, on the reliability of clas￾sical continuum mechanics when scaled outside their validity range, i.e., down to the nano-scale [7]. Thus, it seems desirable to perform a critical review of the current J. Jancar (&) Institute of Materials Chemistry, Brno University of Technology, Brno, Czech Republic e-mail: jancar@fch.vutbr.cz 123 J Mater Sci (2008) 43:6747–6757 DOI 10.1007/s10853-008-2692-0