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A practical and efficient propargylboration of ketones is presented using general allenylboronic acid pinacol esters (allenyl‐Bpins) without a catalyst. This reaction is triggered by in‐situ activation of stable allenyl‐Bpins through the sequential addition of 1.25 equiv. of nBuLi and the prerequisite 2.0 equiv. of TFAA. Under the optimized reaction conditions, the versatile trisubstituted allenyl‐Bpins react with various ketones smoothly to afford a wide range of tert‐homopropargyl alcohols bearing vicinal stereocenters in high yields with good to excellent diastereoselectivities. Furthermore, propargylboration of ketones with chiral trisubstituted allenyl‐Bpins allows for the asymmetric synthesis of chiral tert‐homopropargyl alcohols with a full chirality transfer. [ABSTRACT FROM AUTHOR]

All-metallic sandwich-walled cylindrical and conical structures for aerospace applications often require simultaneous excellent vibration and load-carrying capacities. In the present study, the free vibration and axial compression behaviors of cylindrical and truncated conical sandwich shells with corrugated cores are investigated using a combined experimental and numerical approach. Excellent agreement between experimental measurements and finite element simulations for representative vibration and axial compression characteristics is achieved. Parametric studies based on the response surface model are subsequently performed to quantify the influence of key geometrical parameters on vibration and axial compression performance. A multi-functional collaborative design to meet the requirement of high load-bearing capacity subjected to the constraint of low natural frequency is also carried out, which demonstrates the unique advantages of the novel sandwich-walled shells for aeronautical and astronautical applications. [ABSTRACT FROM AUTHOR]

• Deforming is found to have significant influence on the ballistic performance and perforation modes of thin steel plates. • Deforming affects the ballistic performance of deforming targets by changing the energy dissipation mechanism of the projectile-target system. • Whether deforming targets outperform static targets in ballistic performance depends on deforming states of the targets prior to perforation. • The ballistic performance of deforming targets is found to be sensitive to the projectile nose shape. A combined experimental and numerical investigation is carried out to study systematically the ballistic performance of a metallic plate that deforms continuously under pre-imparted impulsive loading (e.g., due to TNT explosion) before being impacted by a projectile. First, based on a novel experimental method, ballistic impact test of a deforming thin steel plate is performed via an one-stage gas gun; as benchmark, ballistic impact test of a static (non-deforming) thin steel plate via a two-stage gas gun is also performed. Results show that deforming has significant influence on ballistic performance of metallic plates in terms of perforation mode and ballistic limit. Then, based on three-dimensional finite element simulations that are validated against experimental measurements, physical mechanisms underlying the deforming effect are explored. The effects of pre-imparted impulse, the shock resistance of target plate, and the nose shape of projectile on the ballistic performance are also quantified. It is demonstrated that deforming leads to changes of the projectile-target system in three aspects: providing initial kinetic energy to target, changing plastic deformation in dished region, and altering shear force during perforation. The interaction of these three aspects dictates the ballistic performance of a deforming target plate. The results are employed to carry out anti-penetration design for deforming steel plates. [ABSTRACT FROM AUTHOR]

A novel lightweight sandwich construction with square honeycomb-corrugation hybrid core (SHCH) was fabricated by honeycomb-corrugation assembly and vacuum brazing. The out-of-plane quasi-static compression behavior of the hybrid structures was explored in detail by experimental measurement, numerical calculation and theoretical prediction. The proposed brazed structures in high density region are found still to have strength and energy absorption capacity significantly greater than the sum of those of empty corrugated sandwich and square honeycomb-cored sandwich. In addition, the compressive strengths of the proposed square honeycomb–corrugation hybrid cores exhibit obvious superiority over those of competing core topologies in the high-density region. • Novel lightweight sandwich constructions with square honeycomb-filled corrugated hybrid cores are proposed. • The out-of-plane compressive behavior of the hybrid cores is enhanced. • Compressive stiffness, initial failure strength, and failure modes are predicted. • The strength and energy absorption capacity of honeycomb and corrugation in hybrid cores are significantly enhanced. • The compressive strengths of such hybrid cores exhibit obvious superiority in the high-density region. [ABSTRACT FROM AUTHOR]

• A novel composite projectile for simulating combined blast and impact loading has been proposed. • The composite-projectile-based approach is proved to be valid in simulating combined loadings from cased explosives under certain conditions. • Based on the experimental approach, a new synergetic effect of combined blast and single fragment impact loading is found. • The proposed approach provides a chance to investigate ballistic impact of deforming target experimentally. A novel composite projectile is put forward to simulate combined blast and single fragment impact loading, which is comprised of a cylindrical aluminum foam projectile embedded with a fragment simulation projectile (FSP). Comparison between cased explosive and composite projectile in terms of the generated combined loading shows that the composite projectile technique is theoretical feasible. Experimental tests for normal impact of the composite projectile on clamped plates are carried out. Results show that the proposed composite projectile can induce both blast-induced deflection and fragment-induced perforation on the clamped plate. The arrival time interval between blast and fragment has significant influence on the extent of induced damage on the plate and the residual FSP velocity. Numerical simulations with the method of finite elements are carried out to provide further insight into the interaction between the composite projectile and clamped plate, and to explain observations and measurements in experiments. The present study reveals a new synergetic effect of combined blast and single fragment impact loading on clamped plate: arrival time interval between blast and impact loading affects significantly the residual velocity of the FSP. [ABSTRACT FROM AUTHOR]

How sand filling affects the dynamic response of metallic corrugated sandwich beams under shock loading was characterized, both experimentally and numerically, with shock loading simulated by high-speed impact of aluminum foam projectiles at beam mid-span. To facilitate evaluating the effects of sand filling, both empty and sand-filled corrugated core sandwich beams were assessed and compared for shock resistance. Representative deformation processes, deformation and failure modes, and beam deflections were experimentally obtained and analyzed. Sand-filled sandwich beams exhibited much higher shock resistance than the empty ones. Numerical simulations were subsequently conducted using a coupled discrete particle/finite element approach that takes into account the coupling interaction between the sand grains and corrugation members. The simulations predicted reasonably well the primary features (permanent mid-span deflections and deformation modes) of both the empty and sand-filled sandwich beams observed experimentally. The validated numerical model was employed to evaluate how the properties of the filling sand and other granular filling materials, e.g., density, stiffness, friction and damping, affect the shock resistance of sandwich beams. The results indicated that the shock resistance was sensitive to, firstly, the density and stiffness of sand and, secondly, the friction between sand particles. In contrast, the damping between sand particles had little effect. • The response of empty and sand-filled corrugated core sandwich beams under foam impact were obtained and analyzed. • A coupled DEM/FEM approach was proposed and predicted well the primary features of sandwich beams observed experimentally. • The effects of the properties of filling sand on the shock resistance of corrugated core sandwich beams were evaluated. [ABSTRACT FROM AUTHOR]

• Blast resistance of fluid-filled corrugated sandwich beams was investigated experimentally and numerically. • Fluid filling could effectively reduce mid-span deflection of the face sheet and enhance the plastic buckling/progressive folding resistance of the corrugated core. • A combined SPH-FE model of fluid-filled sandwich beams was established to characterize the overall structural response of fluid-filled sandwich beams. • Dependence of permanent mid-span deflection upon fluid filling and sealing material was quantified numerically. The effect of fluid filling on the dynamic response of corrugated sandwich beams under simulated blast loading with close-celled metallic foam projectile was systematically investigated. Deformation and failure modes as well as displacement/contact force/energy absorption histories of water-filled sandwich beams were obtained at different impact levels and compared with those of empty sandwich beams. Subsequently, a combined smoothed particle hydrodynamics-finite element (SPH-FE) model was employed to simulate the dynamic responses of water-filled sandwich beams, explore the underlying mechanisms, and assess the influence of fluid-filling and sealing material on permanent beam deflection. Good agreement was achieved between numerical simulations and experimental measurements. Under impact loading, the filled liquid provides strong interaction between fluid and sandwich components owing to its inertia and incompressibility. Fluid-filling led to not only significantly reduced permanent deflection of both face sheets but also considerably enhanced resistance of the corrugated core against plastic buckling and progressive folding [ABSTRACT FROM AUTHOR]

• Low cycle fatigue behaviour of Cr-coated zirconium fuel cladding was investigated. • Cr coatings were prepared by HiPIMS and DCMS deposition technique, respectively. • HiPIMS-Cr coating has better fatigue performance than DOMS-Cr one. In this paper, the work reports on finding of an experimental investigation of the low cycle fatigue performance of Cr-coated zirconium fuel cladding. Cr coatings were fabricated by utilizing High-power Impulse Magnetron Sputtering (HiPIMS) and Direct Current Magnetron Sputtering (DCMS) deposition techniques, respectively. The experimental results have indicated that, due to the different discharge characteristics of DCMS and HiPIMS, the microstructure and mechanical performances of the deposited Cr coating are significantly different. The film morphology alter from columnar for DCMS-Cr coating to dense for HiPIMS-Cr coating, and the hardness of HiPIMS-Cr coating is higher than the values of DCMS-Cr coating. The low cycle fatigue performance of HiPIMS-Cr coated zirconium fuel cladding is better than that of DCMS-Cr coated ones, which revealed that the dense Cr coating benefitted the low-cycle fatigue life of the zirconium alloy cladding tube. [ABSTRACT FROM AUTHOR]

• A novel truncated-square honeycomb reinforced hollow pyramidal lattice sandwich structure (TSH-HP) was proposed. • The peak strength of TSH-HP is higher than that of hollow pyramid lattice structure with the same mass. • With increasing of temperature, compressive modulus, peak strength and energy absorption performance of TSH-HP decrease significantly. • TSH-HPs exhibit superiority in the specific strength on the material selection map. This paper focuses on the influence of temperatures on the out-of-plane compressive performance of novel truncated-square honeycomb reinforced hollow pyramidal lattice sandwich structure (TSH-HP) by combining theoretical prediction, experiment and finite element analysis. As the temperature go up from 25 ℃ to 450 ℃, compressive modulus, initial failure strength, peak strength and energy-absorption performance of TSH-HPs prepared by selective laser melting (SLM) techniques decrease by 46.2%, 46.9% 42.3% and 46.3%, respectively, which are in well agreement with experiment and numerical simulation. In addition, the initial failure strength and peak strength of TSH-HPs are 5–10% higher than those of hollow pyramid lattice structure (HP) with same mass under different temperature. Compared with competing cellular materials, TSH-HPs exhibit superiority in the specific strength on the material selection map. [ABSTRACT FROM AUTHOR]

• The ballistic resistance of multilayered UHMMPE cross-ply laminates under the impact of blunt projectiles was investigated, both experimentally and numerically. • The penetration resistance could be improved by layering the target, and the enhancement was more pronounced as the number of layers was increased. • Mechanisms underlying the superior ballistic resistance of the multilayered target were discussed. Multilayered cross-ply ultra-high molecular weight polyethylene (UHMWPE) laminated plates were envisioned and their ballistic performance explored, both experimentally and numerically. High velocity impacts were performed on both monolithic and multilayered targets with identical areal density. Ballistic data were obtained, together with dynamic deformation features and failure modes for both target types. Full three-dimensional finite element (FE) simulations were carried out to calculate the dynamic response of each target and explore the underlying mechanisms. Good agreement was achieved between FE simulations and experimental measurements. The results revealed that multi-layering the target could relieve fiber tensile stresses on its rear face and generate a more significant pull-in effect at the edges, resulting in larger back-face deflection and enhanced ballistic resistance. [Display omitted] [ABSTRACT FROM AUTHOR]

• Novel multi-walled tube-reinforced aluminum foam (MWTRF) was proposed. • Combining foam with multi-walled tube leads to dramatic increase in both load bearing and energy absorption. • Foam could effectively enhance the plastic buckling/progressive folding resistance of multi-walled tube. • MWTRF is potentially important for applications demand on simultaneous load bearing and energy absorption. In this paper, a novel multi-walled tube-reinforced aluminum foam (MWTRF) was proposed in an attempt to improve quasi-static compression performances and energy absorption. The quasi-static compression performance of the MWTRF fabricated by combining extrusion and electro-discharge machining (EDM) was investigated through using a combined experimental and numerical method. It is shown that the MWTRF has higher peak load and energy absorption capacity than those of the sum of empty multi-walled tube (EMWT) and aluminum foam (AF). The strengthening mechanism is that AF in MWTRF can stabilizes buckling and changes the compressive deformation mode of EMWT, resulting in elevating compression performance and energy absorption of MWTRF. Moreover, numerical parametric studied on MWTRF reveals that MWTRF with increasing density from the outer foam to the inner foam is the best combination mode with outstanding energy absorption efficiency, and the density of AF and the thickness of EMWT has an impact on the energy absorption capability. Furthermore, in comparison with competing core topologies, the energy absorption of the proposed MWTRF is outstanding on the material selection map. [ABSTRACT FROM AUTHOR]

The ballistic performance of a bi-layer armor encapsulated with ultra-high molecular weight polyethylene (UHMWPE) composite laminate was investigated using a combined experimental and numerical approach. Three series of test specimens were examined: (A) bare and encapsulated aluminum (Al) plates, (B) bare and encapsulated bi-layer mosaic armors, and (C) bi-layer mosaic armors having identical areal density but different encapsulation thicknesses. The ballistic behaviors and failure mechanisms of UHMWPE encapsulated Al plates and bi-layer mosaic armors under different projectile impact velocities were analyzed systematically. Attributed to the integration effect of encapsulation, the encapsulated specimens could effectively disperse localized projectile impacting to the entire structure. The results indicated that the UHMWPE encapsulation could enhance significantly the ballistic resistance of traditional ceramic/metal bi-layer armors, due mainly to serious pulling and stretching deformations of the lateral and rear UHMWPE laminates in resisting the projectile impact. However, thicker encapsulation would not necessarily lead to better ballistic performance for specimens with equal areal density. Further, the thickness (or mass) ratio of the armor substructures needed to be tailored synthetically to achieve optimal ballistic performance. [ABSTRACT FROM AUTHOR]