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In the present study, reverse nonequilibrium molecular dynamics is employed to study thermal resistance across interfaces comprising dimensionally mismatched junctions of single layer graphene floors with (6,6) single-walled carbon nanotube (SWCNT) pillars in 3D carbon nanomaterials. Results obtained from unit cell analysis indicate the presence of notable interfacial thermal resistance in the out-of-plane direction (along the longitudinal axis of the SWCNTs) but negligible resistance in the inplane direction along the graphene floor.The interfacial thermal resistance in the out-of-plane direction is understood to be due to the change in dimensionality as well as phonon spectra mismatch as the phonons propagate from SWCNTs to the graphene sheet and then back again to the SWCNTs.The thermal conductivity of the unit cells was observed to increase nearly linearly with an increase in cell size, that is, pillar height as well as interpillar distance, and approaches a plateau as the pillar height and the interpillar distance approach the critical lengths for ballistic thermal transport in SWCNT and single layer graphene. The results indicate that the thermal transport characteristics of these SWCNT-graphene hybrid structures can be tuned by controlling the SWCNT-graphene junction characteristics as well as the unit cell dimensions. [ABSTRACT FROM AUTHOR]

A characterization device was developed for nanomechanical testing on one-dimensional micro/nanostructures. The tool consists of a nanomanipulator, a three-plate capacitive transducer, and associated probes, and is operated inside a scanning electron microscope. The transducer independently measures force and displacement with micronewton and nanometer sale resolutions, respectively. Tensile testing of a polyaniline microfiber (diameter ∼1 μm) demonstrated the capabilities of the system. Engineering stress versus strain curves exhibited two distinct regions with different Young’s moduli. Failure at the probe-sample weld occurred at ∼67 MPa, suggesting that polyaniline microfibers exhibit a yield stress that is higher than most comparable bulk polymers. [ABSTRACT FROM AUTHOR]

In this paper, we present results of plate impact simulations of shock compressed woven glass fiber-reinforced plastic (GRP) performed using the Arbitrary Lagrangian–Eulerian three-dimensional finite element code. A hyperelastic large-strain-based empirical Continuum Damage Mechanics (CDM) formulation is employed to describe damage initiation and growth in the shock-compressed GRP. The model parameters calibration scheme utilizes the Velocity Interferometer System for Any Reflector normal particle velocity measurements at the free surface of the GRP target plates. The impact velocity in the experiments ranged from 8.5 to 418 m/s. The finite element model considered planar 0°/90° bidirectional plies with an individual ply thickness of 0.68 mm, stacked to reach a total laminate thickness of 6.8 mm. The anisotropic elastic strains were estimated from the experimentally determined tetragonal symmetry stiffness matrix for the GRP. The strain-based damage model captures several salient features observed in the measured free surface particle wave profiles, including the shock rise time, onset of Elastic—Elastic Cracking, and the shape of the nonlinear portion of the experimental particle velocity profiles. The CDM model predicts the dominant damage mode to be matrix microcracking due to shear and the associated bulk expansion (bulking) under the global compressive loading in the plate impact configuration. [ABSTRACT FROM AUTHOR]

• NPI is used to probe the inelastic response and shock impedance of the WC flyer/target. • OPI is used to investigate the critical state of stress for the initiation of dynamic failure in the WC. • The results show the importance of simple-shear loading and its amplitude in the brittle fracture of WC. This article presents results from a series of plate-impact experiments designed to study dynamic response of commercial purity (99.6%) tungsten carbide (WC) under shock-induced normal compression and simultaneous compression-and-shear stress wave loading. The normal shock compression experiments utilize a heated WC flyer plate which impacts a WC target at room temperature, enabling inelastic response of the WC target plate as well as the elevated temperature shock-impedance of the heated WC flyer plate to be probed simultaneously. The measured normal particle velocity profiles at the free surface of the WC target plate exhibit an elastic precursor, which corresponds to a longitudinal stress of ∼5.9–6.2 GPa, and decreasing particle velocity levels in the shocked state with increasing temperature of the WC flyer. The shock impedance of the heated WC flyer is estimated to decrease from 1.05 × 108 to 8.23 × 107 kg/m2s over the temperature range 23–600°C. The simultaneous compression-and-shear loading experiments are conducted using a symmetric oblique plate-impact experimental configuration with progressively increasing angles of inclination (5°, 10°, and 22°), resulting in increasing shear to longitudinal stress ratios upon impact in the WC flyer and target plates. The measured longitudinal and transverse components of the free surface particle velocity in experiments with inclination angles of up to 10° and impact velocities ∼100 m/s (corresponding to shear and longitudinal stress levels of 0.5 GPa and 4.5 GPa, respectively), coincide well with their corresponding elastic particle-velocity predictions. However, the free-surface normal particle velocity profiles for experiments conducted at an oblique impact angle of 22° (corresponding to shear stresses ∼1.3 GPa and longitudinal stress of ∼4.9 GPa) are remarkably different and exhibit a sudden increase in particle velocity from their plateau levels reminiscent of failure waves observed by other investigators in soda lime glass and silicon carbide (SIC-B). The new normal particle velocity level, after the arrival of the recompression/re-acceleration signal, exceeds the magnitude of the impact velocity, suggesting failure of the WC target plate during the stress wave loading process. The relatively large undulations present in the measured free-surface transverse particle velocity profiles provide further evidence for the heterogeneous brittle failure processes in WC under the resulting simple-shear state of stress, and is used to provide estimates for the critical range of simple-shear loading that can initiate catastrophic failure (fracture) in pure WC. [ABSTRACT FROM AUTHOR]

A series of reverse geometry normal plate impact experiments are employed to investigate the incipient plastic behavior of commercial purity polycrystalline aluminum under ultra-high strain-rates (∼10 5 /s) and test temperatures up to melt (i.e. 643   °C). The applied stress at the aluminum/target interface, as inferred from the measured normal free-surface particle velocity record, shows progressive weakening with increasing test temperatures ranging from 23–620   °C; at higher temperatures (470–620   °C) this rate of weakening is observed to decrease, and at the highest test temperatures employed in the study, i.e. temperatures approaching the melt point of aluminum (643   °C), a net increase in the longitudinal stress is observed. Additionally, estimates of longitudinal elastic impedance of the sample material, as inferred via impedance matching from the particle velocity states at shock plateau show similar monotonic decrease with temperature, except for the highest test temperature case, in which reversal of this trend is observed. Though slight, these noticeable changes in the impedance, and stress/velocity states likely indicate variances in the strengthening/hardening response of the material, which can be linked to transition in the dominant plastic flow mechanisms as the sample approaches the melting point. Scanning electron microscopy of the impact surface of the post-test samples reveal coarsening of the sample grains due to static recrystallization during the heating phase of the experiment. Additional experiments are performed on annealed specimens to probe the effects of microstructural changes, i.e. grain size, and/or relief of residual strains in the interpretation of the measured response of aluminum. The results, which show a decrease in the longitudinal acoustic impedance, and decrease in the levels of stress/particle velocity under shock loading, indicate that the effects of annealing may play a role in the observed response by promoting softening of the dynamic strength, and/or lessening of the rate of hardening in a post-yield regime. [ABSTRACT FROM AUTHOR]

Results are presented on the shock response of a zirconium-based bulk metallic glass (BMG), Zr41.25Ti13.75Ni10Cu12.5Be22.5, subjected to planar impact loading. An 82.5-mm bore single-stage gas-gun facility at Case Western Reserve University, Cleveland, OH, was used to conduct the shock experiments. The particle velocity profiles, measured at the back (free) surface of the target plate by using the velocity interferometer system for any reflector (VISAR), were analyzed to (i) better understand the structure of shock waves in BMG subjected to planar shock compression, (ii) estimate residual spall strength of the BMG after different levels of shock compression, and (iii) obtain the Hugoniot elastic limit (HEL) of the material. The spall strength was found to decrease moderately with increasing levels of the applied normal impact stress. The spall strength at a shock-induced stress of 4.4 GPa was 3.5 GPa while the spall strengths at shock-induced stresses of 5.1, 6.0, and 7.0 GPa were 2.72, 2.35, and 2.33 GPa, respectively. The HEL was estimated to be 6.15 GPa. [ABSTRACT FROM AUTHOR]

In the United States there is currently a paucity of available real world minor rear crash data with struck vehicle delta-V, or speed change, less than or equal to 15 kilometers per hour. These data are essential as researchers attempt to define 'whiplash' injury risk potential in these minor crashes. This study analyzed a new set of 105 U.S. minor rear aligned crashes between passenger vehicles. Mean struck vehicle delta-V and acceleration were 6.3 km/h (s.d. = 2.1 km/h) and 1.4 g (s.d. = 0.5 g), respectively. A total of 113 struck vehicle occupants were diagnosed within five weeks post-crash with 761 ICD-9-CM complaints and 427 AIS injuries (99.5% AIS1) attributed to the crashes. No striking vehicle occupants reported complaints. The main ICD-9-CM diagnoses were 40.6% cervical, 22.5% lumbar/sacral and 10.2% thoracic and the main AIS1 diagnoses were 29.7% cervical, 23.2% lumbar/sacral and 14.3% thoracic. The diagnosis disparity was mainly due to coding for pre-existing degenerative diagnosis in ICD-9-CM. Degenerative spine conditions were not significant for increased AIS1 injury risk. Surprisingly, many non-'whiplash' diagnoses were found. The AIS injury diagnosis distribution and frequency in these minor delta-V crashes did not correspond with previous minor rear crash studies. A prospectively collected and unbiased minor rear crash databank in the model of CIREN or NASS is highly desirable to verify or refute these results for the U.S. population since the current study cohort may have been influenced by litigation.