Protective performance of shear stiffening gel-modified foam against ballistic impact:Experimental and numerical study

As one of the most widely used personal protective equipment(PPE),body armors play an important role in protecting the human body from the high-velocity impact of bullets or projectiles.The body torso and critical organs of the wear may suffer severe behind-armor blunt trauma(BABT)even though the impactor is stopped by the body armor.A type of novel composite material through incorporating shear stiffening gel(STG)into ethylene-vinyl acetate(EVA)foam is developed and used as buffer layers to reduce BABT.In this paper,the protective performance of body armors composed of fabric bulletproof layers and a buffer layer made of foam material is investigated both experimentally and numerically.The effectiveness of STG-modified EVA in damage relief is verified by ballistic tests.In parallel with the experimental study,numerical simulations are conducted by LS-DYNA®to investigate the dynamic response of each component and capture the key mechanical parameters,which are hardly obtained from field tests.To fully describe the material behavior under the transient impact,the selected constitutive models take the failure and strain rate effect into consideration.A good agreement between the experimental observations and numerical results is achieved to prove the validity of the modelling method.The tests and simulations show that the impact-induced deformation on the human body is significantly reduced by using STG-modified EVA as the buffering material.The improvement of protective performance is attributed to better dynamic properties and more outstanding energy absorption capability of the composite foam.

In-situ surface decoration of RuO_(2) nanoparticles by laser ablation for improved oxygen evolution reaction activity in both acid and alkali solutions

Improving the OER activity of noble metal-based materials is of profound importance to minimize the usage of noble metals and lower the cost.Here,we report considerable improvement on the catalytic activity of RuO_(2) particles for OER in both alkali and acid environments.The RuO_(2) nanoparticles were treated with a method of pulse laser ablation.Numerous Ru and RuO_(2) clusters were generated at the surface of RuO_(2) nanoparticles after the laser ablation,forming a lychee-shaped morphology.The larger pulse energy RuO_(2) nanoparticles are treated with,the better the OER activity can be.DFT calculations shows that the surface tension induced by the lychee-shaped morphology benefits the OER performance.Our best sample gives an overpotential of 172 mV(at 10 mA cm^(-2))and a Tafel slope of 53.5 mV dec^(-1) in KOH,while an overpotential of 219 mV and a Tafel slope of 44.9 mV dec^(-1) in H_(2)SO_(4),which are of topclass results.This work may inspire a new way to develop high-performance electrocatalysts for OER.

Ideality analysis and general laws of bubble swarm microflow for large-scale gas-liquid microreaction processes

The flow ideality of bubbly microflow remains unclear even though it is vital for the design of microreactors,especially the ideality of bubble swarm microflow for large-scale gas-liquid microreaction processes.This work is the first time to report the ideality analysis of the microbubble swarm in a relatively large microchannel.The bubble swarm microflow has undergone two conditions:quasihomogeneous plug flow and liquid phase/gas-liquid qua si-homogeneous phase two-phase laminar flow.Both the deviations of void fraction and bubble velocity from the ideal plug flow can divide into two parts,and the two transition points simultaneously happen at the velocity ratio of 1.25.There exists a critical capillary number to maintain the quasi-homogeneous plug flow,which could be regarded as the general laws for the design of gas-liquid microreactors.Finally,a novel model is developed to predict the bubble velocity.This work could be very helpful for the large-scale gas-liquid microreactors design.

Dynamic tensile and failure behavior of bi-directional reinforced GFRP materials

In this paper,a series of static/dynamic tensile tests are performed for glass fiber reinforced plastic(GFRP)composites.Using the combination of high-speed photography and digital image correlation(DIC)technology,true stress-strain curves in different directions and strain rates are obtained.We also obtained the dynamic failure strain of the material in different directions,which are used to accurately describe the dynamic tensile and failure behavior of the material.The experimental results show that there is a stiffness change point N in three directions under different strain rate(10-3 s-1,10 s-1,100 s-1)tensile conditions.The stiffness before and after N point is recorded as Einitial and Echanged respectively.The values of Echanged in weft direction and warp direction are about 30%to 50%of Einitial,while Echanged in tilt direction is only about 10%of Einitial.The fiber has the highest strength in the weft direction and the tilt direction has the lowest strength.With the combination of high-speed photography and DIC technology,the dynamic failure parameters of different directions under the strain rate of 100 s-1 are obtained.The dynamic failure strains in three directions are 0.245,0.373 and 0.341,respectively.The parameters are verified by impact three-point bending test.These works can more accurately describe the dynamic mechanical behavior of glass fiber reinforced plastic(GFRP)composites and provide reference for the design of GFRP structures.

A micro-spectrometer with phase modulation array

A micro-spectrometer with phase modulation array is investigated in this paper. The vital component of this micro-spectrometer is a micro-interferometer array, which is built on a charge-coupled device （CCD） or a complementary metal oxide semiconductor （CMOS）. Each element of micro-interferometer array is formed by polymethyl methacrylate （PMMA） grooves with different depth. When we illuminate the surface of the interferom- eter array, different interference intensity distribution would be formed at the bottom of each micro-interferom- eter. Optical power of this by the pixels of CCD substituted into a linear interferometer can be measured or CMOS. The data can be system. By solving the linear system with Tikhonov regularization method, spectrum of the incident beam can be reconstructed. Simulation results prove that the detection range of the spectrometer is a wide wavelength range covering from 300 to 1100 nm. Furthermore, the wavelength resolution of the device reaches picometer level. In comparison with conventional spectrometers, the novel spectrometer has distinct advan- tages of small size, low cost, high resolution, wide spectral measurement range, real-time measurement, and so on.