The effect of strain rate on compressive behavior and failure mechanism of CMDB propellant

The compressive mechanical behavior of composite modified double base(CMDB)propellant was investigated across a wide scope of strain rates ranging from 10^(-3) s^(-1) to 4210 s^(-1) at room temperature,by applying a conventional universal testing machine and a split Hopkinson tension bar(SHPB),respectively.The derived stress-strain curves at different strain rates show a strong rate dependence,indicated that yield stress,ultimate stress and strain energy density of CMDB propellant all increase with strain rate by following a power law function,while the amplification of increase are different.The deformation and damage modes of CMDB propellant has changed from a typical ductile manner(cracking along the axial direction)to a brittle manner(maximum shear failure)with increasing of strain rate.Scanning electron microscopy(SEM)was employed to explore the microscopic failure characteristics of CMDB propellant.Under quasi-static loading,the nearly parallel micro-cracks propagating along the axial direction and the debonding of RDX particle without particle crushing can be observed.While under dynamic loading,the micro-crack is 45 angle to the axial direction,and multiple cracking modes of RDX particles appeared.Finally,the correlation between strain energy density and failure mechanisms of CMDB propellant was revealed by developing four characteristic failure modes.The findings of this study is very important to evaluate the structural integrity of CMDB propellant.

Intrinsically asymmetric atomic character regulates piezoelectricity in two-dimensional materials

Decreasing of layer thickness causes the decrease of polarization until it disappears due to the existence of depolarization field.Therefore,the search for strong piezoelectric materials is highly desirable for multifunctional ultra-thin piezoelectric devices.Herein,we propose a common strategy for achieving strong piezoelectric materials through the electronic asymmetry induced by the intrinsically asymmetric atomic character of different chalcogen atoms.Accordingly,in the tetrahedral lattice structures,for example,M4X3Y3(M=Pd/Ni,X/Y=S,Se or Te,X≠Y)monolayers are proved to display excellent out-of-plane piezoelectricity.Ni4Se3Te3 possesses the largest piezoelectric coefficient d33 of 61.57 pm/V,which is much larger than that of most 2D materials.Enhancing the electronic asymmetry further increases the out-of-plane piezoelectricity of Janus M4X3Y3 materials.Correspondingly,the out-of-plane piezoelectricity is positively correlated with the ratio of electronegativity difference(Red)and the electric dipole moment(P).This work provides alternative materials for energy harvesting nano-devices or self-energized wearable devices,and supplies a valuable guideline for predicting 2D materials with strong out-of-plane piezoelectricity.