Annealing induced microstructure and mechanical property changes of impact resistant polypropylene copolymer

The effects of annealing on microstructure and mechanical properties of an impact resistant polypropylene copolymer(IPC) were investigated. Different annealing temperatures ranging from 80 °C to 160 °C were selected. The phase reorganization of IPC during annealing process was studied through morphological characterization technologies, including scanning electron microscopy(SEM) and transmission electron microscopy(TEM). The crystalline structure changes in the IPC sample, including the i PP matrix and PE component, were investigated using wide angle X-ray diffraction(WAXD) and differential scanning calorimetry(DSC). Dynamic mechanical analysis(DMA) was used to analyze the relaxation extent of IPC before and after annealing. The results showed that annealing induced phase reorganization in IPC and the degree of phase reorganization depended on annealing temperature. The annealed IPC samples exhibited largely increased crystallinity compared with the unannealed one. Intensified damping peak with increased molecular chain mobility was achieved for the annealed IPC samples. At an appropriate annealing temperature(140 °C), largely enhanced impact strength was achieved for the annealed IPC sample. The toughening mechanisms were analyzed based on the phase reorganization and relaxation behavior.     

Explosives properties of high energetic trinitrophenyl nitramide molecules: A DFT and AIM analysis

The high level density functional theory, B3LYP, was proposed for the derivatives of energetic molecule Trinitrophenyl Nitramide [TNPN]: MTNPN, ETNPN and NETNPN respectively, in order to understand its explosive characteristics. The geometrical analysis has been studied from both the polarized, 6-311G⁷ and augmented, aug-cc-pVDZ basis sets, and found consistency between the structural parameters. The bond strength of each molecule has been characterized from Bader’s AIM analysis, thereby correlating the bond topological properties with the impact sensitivity, which predicts that CNO₂ bonds were the weakest and found more sensitive among the rest of the bonds in all three molecules. The impact sensitivity of the molecules was measured in terms of ΔE_LUMO-HOMO, OB₁₀₀, Q_NO2, h₅₀% and V_mid, revealed the high sensitive nature of NETNPN toward the external shock. The reaction surface of all the three molecules has been located from the isosurface of electrostatic potential.     

Compression after impact of flax/PLA biodegradable composites

A study of the impact behaviour and the post-impact residual strength of fully biodegradable composites is presented in this work. To this end, low-velocity impact tests and compressive residual strength tests were carried out on flax/PLA laminates. The results were compared with carbon/epoxy laminates, showing some important advantages in terms of absorbed energy and normalized residual strength. The reason was attributed to different energy absorption mechanisms; the main failure mode in flax/PLA laminates is fibre failure while residual strength of carbon/epoxy laminates is dominated by delaminations.     

Numerical simulation of sphere water entry problem using Eulerian–Lagrangian method

This paper looks at the hydrodynamic’s numerical simulation of a free-falling sphere impacting the free surface of water by using the coupled Eulerian–Lagrangian (CEL) formulation included in the commercial software ABAQUS. A 3D model of a sphere with an unsteady viscous transient flow condition is used for numerical simulation. The simulation is performed for sphere with different density. The simulation results are verified by showing the computed shape of the air cavity, displacement of sphere, pinch-off time and depth that agree well with experimental results.     

Soil stress distribution related to neutralizing antipersonnel landmines from human locomotion and impact mechanisms

Soil stress distribution was investigated to understand and to develop means for detonating or neutralizing antipersonnel landmines. Specifically, the loading patterns within the soil attributable to the human gait, as well as those derived from a mechanism that delivers an impact load that is being developed for neutralizing antipersonnel landmines, were studied. Experiments were conducted in the soil bin facilities in the Department of Agricultural and Bioresource Engineering at the University of Saskatchewan. Both load cells and mechanically reproduced devices (MRDs), buried at depths of 50, 100, 150 and 200 mm, were used to measure the transmitted forces through the soil. The load cells provided measurements of the temporal load patterns as transferred through the soil, whereas the MRDs indicated the ability for the person or mechanism to successfully trigger a typical antipersonnel landmine. Both forces and impulses based on the load cell data were used as measures for comparison. The key results of the investigation showed human locomotion imparted a load of longer duration than did the impact from the mechanical device; the corresponding soil stresses increased with increasing human weight and impact loads; and forces in the soil increased with higher initial soil compaction level.     

The optimal solution of ESG portfolio selection models that are based on the average ESG score

Recently, various models have been proposed to engage portfolio selection or ESG investments. In this brief report, we solve the problem of optimal portfolio selection of arbitrary ESG utility functions where the ESG preference function is based on the average ESG score. The proposed optimal solution shows that the impact of the ESG score and the expected return vectors on the optimal weights are equal, up to a scalar, regardless of the utility function of the investors.     

A theoretical consideration of the ballistic response of continuous graphene membranes

The remarkable properties of graphene, including unusually high mechanical strength and stiffness, have been well-documented. In this paper, we combine an analytical solution for ballistic impact into a thin isotropic membrane, with ab initio density functional theory calculations for graphene under uniaxial tension, to predict the penetration resistance of multi-layer graphene membranes. The calculations show that continuous graphene membranes could enable ballistic barriers of extraordinary performance, enabling resistance to penetration at masses up to 100× lighter than existing state-of-the-art barrier materials. The very high elastic wave speed and strain energy to failure are the major drivers of this increase in performance. However, the in-plane mechanical isotropy of graphene, as compared to conventional orthotropic woven textiles, also contributes significantly to the efficiency of graphene as a barrier material. This result suggests that, for barrier applications, isotropic membranes composed of covalently bonded two-dimensional molecular networks could provide distinct advantages over fiber-based textiles derived from linear polymers.     

A phenomenological model of damage in articular cartilage under impact loading

Damage progression in high-strain rate and impact tests on articular cartilage is considered. A new type of kinetic damage evolution law is proposed and used to draw implications about the accumulated damage and the coefficient of restitution. Based on the developed damage model, a new fracture criterion is introduced.     

负微分迁移率和碰撞电离对GaAs光导开关非线性特性的影响

对GaAs光导开关非线性工作时,负微分迁移率和碰撞电离的作用进行了数值分析,给出了考虑和未考虑碰撞电离作用时的外电路电流输出波形,以及载流子和电场的空间分布和随时间演变的情况.计算表明GaAs材料的负微分迁移率引起的微分负阻,会导致阴极附近电场的动态增强,使得阴极附近的电场达到本征碰撞电离发生的阈值电场,从而引发本征碰撞电离的发生.分析结果表明,碰撞电离可以极大地延长电流输出的时间,但仅考虑负微分迁移率特性的本征碰撞电离过程不足以完全解释观察到的所有非线性现象,必须进一步考虑其它高电场效应.     

Transient mode localization in coupled strongly nonlinear exactly solvable oscillators

Coupled strongly nonlinear oscillators, whose characteristic is close to linear for low amplitudes but becomes infinitely growing as the amplitude approaches certain limit, are considered in this paper. Such a model may serve for understanding the dynamics of elastic structures within the restricted space bounded by stiff constraints. In particular, this study focuses on the evolution of vibration modes as the energy is gradually pumped into or dissipates out of the system. For instance, based on the two degrees of freedom system, it is shown that the in-phase and out-of-phase motions may follow qualitatively different scenarios as the system’ energy increases. So the in-phase mode appears to absorb the energy with equipartition between the masses. In contrast, the out-of-phase mode provides equal energy distribution only until certain critical energy level. Then, as a result of bifurcation of the 1:1 resonance path, one of the masses becomes a dominant energy receiver in such a way that it takes the energy not only from the main source but also from another mass.