Characteristics structure analysis on debris cloud in the hypervelocity impact of disk projectile on thin plate

In this paper,the gauge points setting is introduced in the SPH simulation to analyze the debris cloud structure generated by the hypervelocity impact of disk projectile on thin plate.Compared with the experiments,more detailed information of the debris cloud structure can be classified from the numerical simulation.However,due to the solitary dispersion and overlap display of the particles in the SPH simulation,accurate comparison between numerical and experimental results is difficult to be performed.To track the velocity and spatial distribution of the particles in the debris cloud induced from disk and plate,gauge points are locally set in the single-layer profile in the SPH model.By analyzing the gauge points’spatial coordinate and velocity,the location and velocity of characteristic points in the debris cloud are determined.The boundary of debris cloud is achieved,as well as the fragments distribution outside the main structure of debris cloud.

High specific strength MWCNTs/Mg-14Li-1Al composite prepared by electrophoretic deposition, friction stir processing and cold rolling

Multi-wall carbon nanotubes reinforced Mg-14Li-1Al composite(MWCNTs/Mg-14Li-1Al) was prepared by the processes of electrophoretic deposition, friction stir processing, and cold rolling. The microstructure and mechanical properties of the composite were investigated. The results show that, the microhardness of the composite is up to HV 84.4, which is 91.38% higher than that of the as-cast matrix alloy(HV 44.1). The yield strength and ultimate tensile strength of the composite are 259 and 313 MPa, which are 135.45% and 115.86% higher than those of the as-cast matrix alloy, respectively, and a high specific strength of 221.98 k N·m/kg is obtained. In the composite, the MWCNTs serve as nucleation particles during the friction stir processing and cold rolling, causing dynamic recrystallization and grain refinement. Furthermore, MWCNTs hinder the movement of dislocations and transfer the load from the matrix alloy, thus improving the strength.

Stress-induced Solid-Solid Crystal Transition in Trans-1,4-polyisoprene

The polymorphic transition of trans-1,4-polyisoprene(TPI) during stretching was investigated by in situ wide-angle X-ray diffraction and Fourier transform infrared spectroscopy. The influences of the initial structure, stretching temperature, and strain rate on the contents of different crystal modifications(α, β) were explored. The results confirm that the α-β transition occurs during stretching of TPI that only contains αcrystal(α-TPI). When the stress is relaxed, the β crystal formed during stretching remains, which indicates that the transition is irreversible. On the other hand, stretching of TPI that only contains β crystal(β-TPI) results in orientated β crystal. No β-α transition occurs during stretching. The different structures of stretched α-TPI and β-TPI exclude the previously proposed "melting-recrystallization mechanism". The α-β transition depends significantly on temperature and strain rate, indicating the transition is governed both by thermodynamics and kinetics. Our results support a solid-solid transition mechanism rather than a melting-recrystallization mechanism. The irreversible nature of the transition is attributed to the metastability of the β phase in the unstretched state. Different from the "β phases" that appear in polymers with stress-induced reversible transitions, e.g. poly(butylene terephthalate) and poly(butylene succinate), the stability of β phase in TPI is high that can be long-lived.The strain rate dependence of α-β transition hinders the determination of critical stress for the transition. It further indicates that the local stress within the sample is more heterogeneous at higher strain rates.

Investigation on structural changes of isotactic polypropylene mesophase in the heating process by using two-dimensional infrared correlation spectroscopy

Two-dimensional FT-IR correlation spectroscopy was used to reveal the structural changes of isotactic polypropylene（iPP） mesophase during the heating process.The co-relationship among the regular helical bands of iPP was discussed according to synchronous spectrum.The results show that the segments with different length-helixes were found to undergo a disordered process in the temperature range of 25-60 ℃.