Microstructure and impact behavior of Mg-4Al-5RE-xGd cast magnesium alloys

This work investigated the microstructure and impact behavior of Mg-4Al-5RE-xGd(RE represents La-Ce mischmetal;x=0,0.2,0.7 wt.%)alloys cast by high-pressure die casting(HPDC),permanent mold casting(PMC),and sand casting(SC)techniques.The results indicated that with increasing Gd content,the grain sizes of the HPDC alloy had a slight change,but the grains of the PMC and SC alloys were significantly refined.Besides,the acicular Al_(11)RE_(3)phase was modified into the short-rod shape under the three casting conditions.The impact toughness of the studied alloy was mainly dominated by the absorbed energy during the crack initiation.With increasing Gd content,the impact toughness of the studied alloy monotonically increased due to the lower tendency of the modified second phase toward crack initiation.The impact stress was higher than the tensile stress,exhibiting a strain rate sensitivity for the mechanical response;however,the HPDC alloy had an inconsistent strain rate sensitivity during the impact event due to the transformation of the deformation mechanism from twinning to slip with increasing strain.Abundant dimples covered the fracture surface of the fine-grained HPDC alloys,indicating a typical ductile fracture.Nevertheless,due to the deficient{1012}twinning activity and the suppressed grain boundary sliding during the impact event,the HPDC alloys showed insufficient plastic deformation capacity.

Internet Through Mobile Phone and Its Cognitive and Behavioral Impact： Changing Sexuality

This study investigates how Internet media in the mobile phone influence on the cognitive and behavioral aspects of human sexuality. Sex is being deviating from socially accepted behaviors; ranging from bisexuality to homosexuality. Based on the qualitative methodology using particular case studies and textual analysis as well as survey research leading to quantitative methodology, this assumes of a transition of cultures as a result of the thorough impact of Internet towards society. In conclusion, lnternet implicit practices in the Mobile Phone in youth and teen societies storms a big change in sexuality, is also affecting towards the human cognitive and behavioral phases of the social life in traditional Buddhist rural village setting in Sri Lanka.

Deformation Behavior and Formability of Gradient Nano-grained AISI 304 Stainless Steel Processed by Ultrasonic Impact Treatment

The deformation behavior and formability of gradient nano-grained（GNG） AISI 304 stainless steel in uniaxial and biaxial states were investigated by means of tensile test and small punch test（SPT）. The GNG top layer was fabricated on coarse grains（CG） AISI 304 by ultrasonic impact treatment. The results showed that the CG substrate could effectively suppress the strain localization of NC in GNG layer, and an approximate linear relationship existed between the thickness of substrate（h） and uniform true strain before necking（ε_（unif））. Grain growth of NC was observed at the stress state with high Stress triaxiality T, which led to better ductility of GNG/CG 304 in SPT, as well as similar true strain after the onset of necking（ε_（neck）） compared with coarse 304 in tensile test. Ei-values of GNG/CG 304 with different structures were nearly the same at different punch speeds, and good formability of GNG/CG 304 was demonstrated. However, punch speed and microstructure needed to be optimized to avoid much lost of membrane strain region in biaxial stress state.

Development and Impact Behaviors of FRP Guarder Belt for Side Collision of Automobiles

In automobiles, the CFRP （carbon fiber reinforced plastics） has a possibility of weight reduction in automotive structures which can contribute to improve mileage and then reduce carbon dioxide. On the other hand, the safety of collision should be also made clear in the case of employing the CFRP to automotive structures. In this paper, the CFRP guarder belt equipped in the automotive door is developed and examined by an experiment and a numerical analysis for replacing the conventional steel door guarder beam. As the experimental relation of impact load to displacement for CFRP guarder belt agreed well with that of numerical result, the numerical method developed here is quite useful for estimating impact behaviors of CFRP guarder belt.

Experimental investigation on enhanced damage to fuel tanks by reactive projectiles impact

Enhanced damage to the full-filled fuel tank,impacted by the cold pressed and sintered PTFE/Al/W reactive material projectile(RMP)with a density of 7.8 g/cm3,is investigated experimentally and theoretically.The fuel tank is a rectangular structure,welded by six pieces of 2024 aluminum plate with a thickness of 6 mm,and filled with RP-3 aviation kerosene.Experimental results show that the kerosene is ignited by the RMP impact at a velocity above 1062 m/s,and a novel interior ignition phenomenon which is closely related to the rupture effect of the fuel tank is observed.However,the traditional steel projectile with the same mass and dimension requires a velocity up to 1649 m/s to ignite the kerosene.Based on the experimental results,the radial pressure field is considered to be the main reason for the shear failure of weld.For mechanism considerations,the chemical energy released by the RMP enhances the hydrodynamic ram(HRAM)effect and provides additional ignition sources inside the fuel tank,thereby enhancing both rupture and ignition effects.Moreover,to further understand the enhanced ignition effect of RMP,the reactive debris temperature inside the kerosene is analyzed theoretically.The initiated reactive debris with high temperature provides effective interior ignition sources to ignite the kerosene,resulting in the enhanced ignition of the kerosene.

Effects of Stacking Sequence and Impactor Diameter on Impact Damage of Glass Fiber Reinforced Aluminum Alloy Laminate

The methods of numerical simulation and test are combined to analyze the impact behavior of glass fiber reinforced aluminum alloy laminate(GLARE).A new failure criteria is proposed to obtain the impact failure of GLARE,and combined with material progressive damage method by writing code of LS-DYNA.Low velocity impact test of GLARE is employed to validate the feasibility of the finite element model established.The simulation results have been shown that progressive damage finite element model established is reliable.Through the application of the finite element model established,the delamination of GLARE evolution progress is simulated,various failure modes of GLARE during impact are obtained,and the effects of stacking sequence and impactor diameter on the impact damage of GLARE are obtained.

Bionic stab-resistant body armor based on triangular pyramid structure

A stab-resistant substrate was designed and realized with a triangular pyramidal structure, inspired by the biological armor model in nature. The stab-resistance behavior and dynamic response mechanisms were studied through numerical simulation and experimental testing of a knife impacting a substrate,and an optimal structural design was obtained accordingly, with a tilted angle of 22.5and optimal thickness of 1.2 mm. It was shown that the triangular pyramidal structure generated twice the internal energy of the knife than the flat substrate due to the dispersing effect of the structure. The force parallel to the inclination caused a significant scratch on the substrate surface, while the force perpendicular caused obvious substrate deformation. A new riveting method was used to form the total layer, which passed the GA 68-2008 standard. The stab-resistant clothing coupled with the reduced wearing burden could provide effective protection and avoid fatal injuries on security personnel working in dangerous environments. The method provided may enlighten the future design and manufacturing of stabresistant clothing.

Energy Absorption Characteristics of Single-walled Carbon Nanotubes

The excellent mechanical properties of carbon nanotubes make them potential candidates for engineering application. In this paper, the impact and failure behaviors of single-walled carbon nanotubes （SWCNTs） are investigated. The effects of diameter, length, and chirality on their energy absorption characteristics under lateral impact and axial crush are studied. By integrating the principle of molecular structural mechanics （MSM） into finite element method （FEM）, the locations and directions of fracture process can be predicted. It is shown that the specific energy absorption （SEA） of SWCNTs is 1-2 order of magnitude higher than that of the ordinary metallic materials and composites in axial impact, indicating that carbon nanotubes are promising energy absorption materials for engineering applications.

An experimental study on the impact behavior of cavitation inside tip clearance of a hydrofoil

Tip clearance cavitation is one of the most common cavitation phenomena exist on duct propellers,pumps and some hydraulic turbines,which may lead to erosion of the components.Due to the influence of the nearby wall,cavitation inside the tip clearance is more complicated than other cases without interaction.So far,the understanding about the impact mechanism of tip clearance cavitation is still limited.In this paper,to obtain the impact behavior of tip clearance cavitation,a high-speed camera was used to capture the cavitation behavior inside the tip clearance of a hydrofoil,and surface paint coating peeling method was applied to show the impact region.Results indicated that cavitation around the tip of the hydrofoil was composed of a tip separation cavity and a tip leakage vortex cavity,and the one with contribution to impact was the tip separation cavity.Through the comprehensive analysis of the paint peeling region and dynamic behavior of tip separation cavity,the impact was found to be related to the local collapse and rebound of the cloud cavitation shed from the attached part.In addition,the influence of tip clearance size on the behavior of tip clearance cavitation was also investigated.As the tip clearance size increased,the tip separation cavity tended to transfer from sheet cavitation to vortex cavitation.These findings can provide a sound basis for evaluating the erosion risk arising from the tip clearance cavitation.

Sinusoidally architected helicoidal composites inspired by the dactyl club of mantis shrimp

The impact region of the dactyl club of mantis shrimp features a rare sinusoidally helicoidal architecture,contributing to its efficient impact-resistant characteristics.This study aims to attain bioinspired sinusoidally architected composites from a practical engineering way.Morphological features of plain-woven fabric were characterized,which demonstrated that the interweaving warp and weft yarns exhibited a sinusoidal architecture.Interconnected woven composites were thus employed and helicoidally stacked to achieve the desired structure.Quasi-static three-point bending and low-velocity impact tests were subsequently performed to evaluate their mechanical performance.Under three-point bending condi-tion,the dominant failure mode gradually changed from fiber breakage to delamination with the increase in the pitch angle.Failure displacement and energy absorption of the heli-coidal woven composites were,respectively,43.89%and 141.90%greater than the unidirectional ones.Under low-velo-city impact condition,the damage area of the helicoidal woven composites decreased by 49.66%while the residual strength increased by 10.10%compared with those of the unidirectional ones,exhibiting better damage resistance and tolerance.Also,effects of fiber architecture on mechanical properties were examined.This work will shed light on future design of the next-generation impact-resistant architected composites.

Intelligent Detection and Identification in Fiber-Optical Perimeter Intrusion Monitoring System Based on the FBG Sensor Network

A real-time intelligent fiber-optic perimeter intrusion detection system （PIDS） based on the fiber Bragg grating （FBG） sensor network is presented in this paper. To distinguish the effects of different intrusion events, a novel real-time behavior impact classification method is proposed based on the essential statistical characteristics of signal＇s profile in the time domain. The features are extracted by the principal component analysis （PCA）, which are then used to identify the event with a K-nearest neighbor classifier. Simulation and field tests are both carried out to validate its effectiveness. The average identification rate （IR） for five sample signals in the simulation test is as high as 96.67%, and the recognition rate for eight typical signals in the field test can also be achieved up to 96.52%, which includes both the fence-mounted and the ground-buried sensing signals. Besides, critically high detection rate （DR） and low false alarm rate （FAR） can be simultaneously obtained based on the autocorrelation characteristics analysis and a hierarchical detection and identification flow.

Enhanced dynamic deformability and strengthening effect via twinning and microbanding in high density NiCoFeCrMoW high-entropy alloys

High density alloys with enhanced deformability and strength are urgently required in energy,military and nuclear industries,etc.In this work,we present a new kind of NiCoFeCrMoW high entropy alloys(HEAs)which possess higher densities and sound velocities than copper.We systematically investigate the phase structure,quasi-static tensile,dynamic compression and related deformation mechanism of these HEAs.It is shown that single FCC or FCC+μdual phases were formed in the HEAs depending on Mo and W content and annealing temperature.Excellent quasi-static tensile and dynamic compression properties have been achieved for these HEAs,e.g.Ni_(30)Co_(30)Fe_(21)Cr_(10)W_(9)HEA annealed at 1573 K exhibited a yield and ultimate tensile strength and elongation of~364 MPa,~866 MPa and~32%,respectively,in quasi-static test;a yield strength of~710 MPa and no fracture under the dynamic strain rate of 4100 s^(-1).Superior strain rate sensitivity(SRS)of yield strength than that of previously reported FCC HEAs have been evidenced.The dynamic stress-strain constitutive relation can be described by the modified Johnson-Cook model.As for the dynamic deformation mechanism,it is envisaged that the regulation of stacking fault energy and Peierls barrier in current HEAs resulted in occurrences of abundant nanoscale deformation twins and microbands during high strain rate compression.The synergistic microbanding and twinning effectively contributes to the enhanced dynamic deformability and strengthening effect.Besides,the interactions of dislocations with precipitates,stacking faults(SFs)with twins,and between SFs also contribute to extraordinary work-hardening capacity.

Modeling and analysis of knee joint impact damage in triple jump manipulators based on finite element method

In order to study the three jump training and competition on knee joint impact damage degree,left knee joint of one healthy male athletes is used as the research object,a complete knee three-dimensional model was established based on the jumper’s knee CT scan and magnetic resonance imaging(MRI),including the femur,tibia,fibula,patella and knee major cartilage,ligaments.The multi-body dynamics analysis(MDA)and finite element analysis(FEA)method are used to calculate the three jump,jump starting,landing process of athletes knee joint impact,the state should change the status of stress,strain and displacement.The results show that in the three jump process,the load on the lateral contact area of the knee joint is the largest,the displacement is the largest,and it increases with the impact of jump and landing.This exacerbated the degree of wear and tear of the tibia,it tends to induce knee injury in athletes.The results show that the combination of finite element and MDA can better study the knee joint’s shock and vibration during the three-level jump training and competition,and these open up a new research method for the knee joint injury.It also provides a certain reference for the prevention and treatment of knee joint injury.

The dynamic compressive properties of magnetorheological plastomers: enhanced magnetic-induced stresses by non-magnetic particles

In this research, a series of hollow glass powder(HGP) reinforced magnetorheological plastomers(MRPs)were prepared to improve the impact resistance of the materials, and the dynamic compressive properties of MRPs under high strain rate were investigated by using a split Hopkinson pressure bar(SHPB)system equipped with a customized magnetic device. Experimental results showed the HGPs greatly enhanced the yield stresses of the MRPs. Especially, for MRPs with 9 vol.% carbonyl iron powders(CIPs), the magnetic-induced yield stress increased from 7.3 MPa to 17.1 MPa(134% increased) by adding 18 vol.%HGPs. The particle structures in MRPs were further simulated and the corresponding intergranular stress was calculated to study the enhancement effect of HGPs. The simulated results showed that more compact structures were formed with the excluded volume caused by secondary HGPs, so the yield stresses of the MRPs increased under a magnetic field. However, when the mass ratio of HGP to CIP was larger than 0.67, HGPs would hinder the formation of chain-like structures and reduce the magneto-mechanical properties. As a result, the replacing of CIPs by HGPs was proven to be an excellent strategy to improve the dynamic properties of MRPs.