1 The tensile and shear failure behavior dependence on chain length and temperature in amorphous polymers Junhua Zhao * , Timon Rabczuk * Institute of Structural Mechanics, Bauhaus-University Weimar, 99423 Weimar, Germany * Corresponding author: junhua.zhao@uni-weimar.de ; timon.rabczuk@uni-weimar.de Abstract The tensile and shear failure behavior dependence on chain length and temperature in amorphous polymers are scrutinized using molecular dynamics simulations. A wide range chain length of alkane is tested under tension and shear with various temperatures. We find that the broken rate (the broken bond number to all polymer chain number ratios) under tension and shear increases with increasing chain length and temperature. For a given chain length and temperature, the broken rates under shear are always higher than those under tension at a same large strain. For a given chain length, the tensile and shear stresses decrease with increasing temperature. We propose three typical fracture mechanisms to effectively elucidate the ductile fracture response based on the predominance of chain scission process. Keywords Failure, Chain length, Linear polymers, Molecular dynamics. 1. Introduction Amorphous polymers are one of the most fundamental polymer molecular shapes that have widely been investigated by many researchers due to the important physical and chemical properties [1,2]. Glass forming polymers (T<T g , T g is the glass-transition temperature) are of great industrial importance and scientific interest. Their unique mechanical properties arise from the connectivity and random-walk-like structure of the constituent chains [3]. At very small strains, the response is elastic. At slightly larger strains, yielding occurs when intermolecular barriers to segmental rearrangements are overcome. Following yield, the material may exhibit strain softening, a reduction in stress to a level corresponding to plastic flow. At higher strains, the stress increases as the chain molecules orient, in a process known as strain hardening. Strain hardening suppresses strain localization (crazing, necking, shear banding) and is critical in determining material properties such as toughness and wear resistance [4,5]. In the other hand, the yield point of the polymers disappears after T>T g . Recently, we have found that the chain length (CL) and temperature have a large effect on the thermomechanical properties of linear polymers [6-8] based on united-atom (UA) and coarse-grained (CG) molecular dynamics (MD) simulations. Since the UA and CG potentials limitations, the effect of the CL and temperature on the failure behavior is not understood well yet. Especially, the failure behavior under shear has been scarcely reported in previous work. Therefore, understanding the molecular origins of macroscopic fracture behavior such as fracture energy is a fundamental scientific challenge [5,9]. In this paper, the tensile and shear failure behavior dependence on CL and temperature in linear polymers are scrutinized using MD simulations. A wide range chain length of alkane is tested under tension and shear with various temperatures. The fracture mechanism is proposed based on the detailed analysis of the fracture response. 2. Simulations details