Rear Layer Research Articles

Optimum design of double-layer target for proton acceleration by ultrahigh intense femtosecond lasers considering relativistic rising edge.

Advances in laser technology have led to ever-increasing laser intensities. As a result, in addition to the amplified spontaneous emission and pedestal, it has become necessary to accurately treat the relativistic rising edge component. This component has not needed much consideration in the past because of its not relativistic intensity. In the previous study, a thin contamination layer was blown away from the target by the rear sheath field due to the relativistic rising edge component, and the target bulk was accelerated by the sheath field due to the main pulse. These indicated that the proton acceleration is not efficient in the target normal sheath acceleration by the ultrahigh intense femtosecond laser if the proton-containing layer is as thin as the contamination layer. Here we employ a double-layer target, making the second (rear) layer thick enough not to be blown away by the rising edge, so that the second layer is accelerated by the main pulse. The first layer is composed of heavy ions to reduce the total thickness of the target for efficient proton acceleration. We investigate an optimal design of a double-layer target for proton acceleration by the ultrahigh intense femtosecond laser considering the relativistic rising edge using two-dimensional particle-in-cell simulations. We also discuss how to optimize the design of such a double-layer target and find that it can be designed with two conditions: the first layer is not penetrated by hole boring, and the second layer is not blown away by the rising edge.

Blast protection of steel reinforced concrete structures using composite foam-core sacrificial cladding

The current investigation presents the effectiveness of a composite foam-core sacrificial cladding for blast protection of steel Reinforced Concrete (RC) structures using explicit finite element analysis in LS-DYNA. Fluid-structure interaction (FSI) methodology was employed to obtain the deformation and damage of steel-reinforced concrete columns under explosive impact. The purpose of this research is to demonstrate the effectiveness of an array of PVC foam cones used as the back layer of a composite sacrificial cladding to protect RC structures from close-in explosions. Simulations were carried out for several blast loading conditions by changing the explosive mass and the stand-off distance. The study was divided into two parts; first, the response of the RC column under blast loading was analyzed and, afterwards, the column was re-examined with the use of composite sacrificial cladding attached on its façade. Based on the analyses, it was proved that the foam conical-array configuration developed in this work that consists the rear layer of the composite sacrificial cladding, reduces the peak force applied on the concrete structure by 50% compared against the same protective configuration, where a uniform rear foam layer of the same thickness was used, whereas it is by 71% lighter than the conventional sheet core.

Numerical and Experimental Study of Hybrid Composite Body Armor

Kevlar is widely used in ballistic applications to protect against hand pistols, due to its high strength, lightweight, and high impact resistance. Compared to other fabrics, Kevlar is considered a typical material due to its strength properties for bullet-proof vests. This project aims to develop a hybrid composite and investigate its behavior under ballistic impact both experimentally and theoretically. Ceramic/woven fabric reinforced epoxy/polycarbonate multilayered armors were developed. The initial layer of defense against the bullet is silicon carbide (SiC). The intermediate composite is made up of aramid fabric (Kevlar) reinforced epoxy (KEV/EPX). The rear layer was made of polycarbonate (PC). A 9 mm FMJ bullet was fired in 310 m/s, towards samples of 900 cm2. To simulate the ballistic test, Ansys Workbench Explicit Dynamics and Ansys AUTODYN 3D were used. An integrated methodological approach of experimentation and simulation was followed to assess the behavior of samples. Obtained results showed that SiC+ KEV/EPX+ polycarbonate was able to stop the 9mm FMJ bullet and indicated that armor layers perforated without penetration. Back Face Signature BFS was also measured, which is within the allowed limit. The ceramic layer absorbs the largest percentage of the overall energy absorbed, compared to fiber-reinforced epoxy and polycarbonate, which reach 77.8% of the entire energy.

High-velocity impact behavior of hybrid fiber-reinforced epoxy composites

In this study, non-hybrid and hybrid (Kevlar, carbon and glass) fabric epoxy composite laminates were fabricated with different stacking sequences by hand lay-up followed by hot-compression molding. Experimental tests were conducted to investigate tensile, flexural, and hardness characteristics. It was found that the stacking sequence did not significantly affect the tensile strength and hardness values of the composites; however, it affected their flexural strength. Damage morphology of the specimens through SEM images showed that the major damage mechanisms in the composites were delamination, fiber breakage, pull-out, and matrix cracking. Based on the static experimental results, the high-velocity impact behavior was investigated through simulation study using LS-DYNA finite element analysis (FEA) software. To study the ballistic impact, a steel projectile with a hemispherical penetrating edge at impact velocities of 100 m.s−1, 250 m.s−1, and 350 m.s−1 was considered. Among non-hybrid fabric epoxy composite specimens, Kevlar/epoxy specimen was found to have the highest impact energy absorption followed by carbon/epoxy and glass/epoxy, respectively. Regarding the hybrid fabric epoxy composite specimens, the ones with Kevlar plies in the rear face exhibited better energy absorption compared to other stacking sequences. The non-hybrid glass/epoxy specimen had the lowest energy absorption and highest post-impact residual velocity of projectile among all specimens. From the FEA results, it was noted that impact resistance of hybrid composites improved when Kevlar fabric was placed in the rear layer. Thus, the stacking sequence was observed to be of substantial importance in the development of fabric-reinforced composite laminates for high-velocity impact applications.

Diffusion Bonding of High-Alloyed Tool Steels with Maraging and Precipitation Hardening Steels

Steel composites for application as protective plates were produced via diffusion bonding. Cold work tool steels were combined with a precipitation hardening steel or a maraging steel using a deformation dilatometer and a vacuum furnace at 1150 °C for 8 h in total. Subsequently, a heat treatment was applied to achieve the final mechanical properties. The microstructure of the interface was investigated by optical microscopy, scanning electron microscopy, electron backscatter diffraction, energy dispersive X-ray spectroscopy and hardness measurements. The results are compared with a simulation of the diffusion of elements performed by MatCalc. Both composites achieve high hardness near the surface of the cold work tool steels, which can have a positive effect on the destruction of projectiles on impact. The influence of carbon diffusion can be observed up to a depth of 3 mm from the interface. As a result of carbon diffusion, soft zones are formed on both sides of the interface, which can be attributed to decarburization, phase transformation and carbide formation. The tough back layer is designed to absorb the remaining energy of the projectile. The combination of a hard front layer and a tough rear layer provides an optimal combination of materials against ballistic threats.

Two-temperature Navier-Stokes equations for a polyatomic gas derived from kinetic theory.

A polyatomic gas with slow relaxation of the internal modes is considered, and the Navier-Stokes equations with two temperatures, the translational and internal temperatures, are derived for such a gas on the basis of the ellipsoidal-statistical (ES) model of the Boltzmann equation for a polyatomic gas, proposed by Andries etal. [Eur. J. Mech. B, Fluids 19, 813 (2000)10.1016/S0997-7546(00)01103-1], by the Chapman-Enskog procedure. Then, the derived equations are applied to numerically investigate the structure of a plane shock wave in CO_{2} gas, which is known to have slowly relaxing internal modes. The results show good agreement with those obtained by the direct numerical analysis of the ES model for moderately strong shock waves. In particular, the results perfectly reproduce the double-layer structure of the shock profiles consisting of a thin front layer with rapid change and a thick rear layer with slow relaxation of the internal modes.

Resistance of multi-layered UHPFRC against in-service projectile: Experimental investigation and modelling prediction

The present paper studies the ballistic performance of Ultra-High Performance Fiber Reinforced Concrete (UHPFRC) applying multi-layered concept against the 7.62 mm projectile at 840 m/s. Coarse basalt aggregates are incorporated in the UHPFRC under the premise of reducing the cement powder consumption and taking advantages of their superior ballistic resistance. We found that the designed triple-layered UHPFRC 16a1s(40)-8a1s(10)-16a1s(40) achieves a superior impact resistance compared to the single-layered reference, with a 32% reduction of the penetration depth. The improved resistance of the triple-layered UHPFRC is associated with the multiple effects of the coarse aggregate, the layer interface, the fibers direction in the thin middle layer, and the edge confinement of the rear layer. Moreover, a new analytical model is proposed to predict the penetration depth in the multi-layered UHFRC, which can take the varying mechanical properties of the layered targets into consideration. The results from this study shed light on understanding the ballistic performance of layered UHPFRC, and promote its application in protective constructions.

Implantation‐based passivating contacts for crystalline silicon front/rear contacted solar cells

AbstractIn this work, we develop SiOx/poly‐Si carrier‐selective contacts grown by low‐pressure chemical vapor deposition and boron or phosphorus doped by ion implantation. We investigate their passivation properties on symmetric structures while varying the thickness of poly‐Si in a wide range (20‐250 nm). Dose and energy of implantation as well as temperature and time of annealing were optimized, achieving implied open‐circuit voltage well above 700 mV for electron‐selective contacts regardless the poly‐Si layer thickness. In case of hole‐selective contacts, the passivation quality decreases by thinning the poly‐Si layer. For both poly‐Si doping types, forming gas annealing helps to augment the passivation quality. The optimized doped poly‐Si layers are then implemented in c‐Si solar cells featuring SiO2/poly‐Si contacts with different polarities on both front and rear sides in a lean manufacturing process free from transparent conductive oxide (TCO). At cell level, open‐circuit voltage degrades when thinner p‐type poly‐Si layer is employed, while a consistent gain in short circuit current is measured when front poly‐Si thickness is thinned down from 250 to 35 nm (up to +4 mA/cm2). We circumvent this limitation by decoupling front and rear layer thickness obtaining, on one hand, reasonably high current (JSC‐EQE = 38.2 mA/cm2) and, on the other hand, relatively high VOC of approximately 690 mV. The best TCO‐free device using Ti‐seeded Cu‐plated front contact exhibits a fill factor of 75.2% and conversion efficiency of 19.6%.

Crystalline silicon photovoltaic cells used for power transmission from solar-pumped lasers: III. Prototype for proof of the light trapping concept

We have proven the light trapping concept for crystalline silicon (c-Si) photovoltaic (PV) cells used for power transmission from solar-pumped lasers (SPLs) emitting at 1064 nm. We fabricated a prototype of the PV cells in which four unique features were employed: (i) a 45-µm-thick c-Si wafer and an aperture of 100 µm diameter, (ii) a bandpass filter on the front surface and a diffuse reflector on the rear surface, (iii) a p+/p/n+ configuration illuminated from the p+-layer, and (iv) an Al/Ag double-layered electrode on the p+-front layer and a Ag electrode on the n+-rear layer for compatibility of ohmic contacts and high reflectance. Under 1064 nm laser illumination at 4.8 W/cm2, the external quantum efficiency was as high as 0.92 despite the use of a thin c-Si wafer, resulting in a conversion efficiency of around 35%. No marked detrimental effect was observed under more intense illumination up to 21.3 W/cm2.

Axial compression behaviour of cross laminated wood-wool panel wallettes

This study reported on the investigation of the structural behaviour of wallettes fabricated using wood-wool cement panel (WWCP) under axial compression load. WWCP is a wood based product, which produced by mixing a wood-wool, cement and water and compressed to form a stable panel with dimension of 600 mm × 2400 mm × 50 mm. In the fabrication of wallettes, two parameters were considered which are wallettes without surface plaster denoted as WNP and wallettes with 16 mm thickness of surface plaster on both sides denoted as WP. The 50 mm thickness of WWCP was used and cut into size 300 mm and 600 mm length. The cut panels were then horizontally laid in two layers (each layer consists of two panel strips) at different panel orientation to form a 600 mm × 600 mm wallettes. The front and rear layer were bonded together using 15 mm thick of normal mortar mix at a mixing ratio of 1: 3 (Cement : Fine sand). A total of five wallettes specimens were fabricated and tested under axial compression load test until failure. The testing results indicated that, the application of surface plaster on both side significantly increased the load carrying capacity of wallettes about 31 % compared to the wallettes without surface plaster.

Analysis of Local Aluminum Rear Contacts of Bifacial PERC+ Solar Cells

A recently published industrial passivated emitter rear contact (PERC) solar cell concept called PERC+ enables bifacial applications by printing an aluminum (Al) finger grid instead of the full-area Al layer aligned to the laser contact openings on the rear side. We demonstrate that the rear contacts of these PERC+ solar cells exhibit back-surface field (BSF) depths of around 6 μm over a large range of contact linewidths, whereas PERC cells with full-area Al rear layer show a reduction of the Al-BSF depths for narrower contact lines. Using an existing analytical model for the local contact formation, we show that the measured Al-BSF depths are well described solely by the different volume of Al paste printed on the rear side. Consequently, the open-circuit voltage of PERC+ solar cells improves by up to 5 mV when reducing the contact linewidth only. In contrast, for PERC cells with full-area Al layer, the V oc slightly decreases with narrower contact linewidths due to the thinner Al-BSF depths. We observe a strongly reduced number of voids in the Al–Si eutectic layer for PERC+ cells, compared with PERC. As physical root cause for void formation, we propose the minimization of surface energy of the Al–Si melt.

Fracture mechanism of a laminated aluminum alloy plate during ballistic impact

The multilayered 7XXX series aluminum alloy was impacted by 7.62 mm ogival projectiles at velocities ranging from 787 to 851 m·s−1. The deformed microstructure under various impacting velocities and fracture surfaces of different sections were investigated at different physical scales to determine the process of failure. Optical microscopy (OM), electron back-scattered diffraction (EBSD) and scanning electron microscopy (SEM) were used in the investigation. The results show that crater is constrained in the 7B52 front layer and two types of adiabatic shear bands which are transformed bands and deformed bands and different types of cracks are observed. Spall fracture is the significant failure mode of 7B52 front layer, and the resulting delamination leads to the presence of bending tensile fracture instead of the shear plugging. The ductile 7A01 layer blunts and deflects the spall crack tips, preventing the targets from full spall, and induces a constraint of 7A52 rear layer. The level of the constraint determines different fracture modes of 7A52 layer, accounting for the asymmetry of damage.

PERC+: industrial PERC solar cells with rear Al grid enabling bifaciality and reduced Al paste consumption

AbstractPassivated emitter and rear cell (PERC) solar cells are currently being introduced into mass production. In this paper, we report a novel PERC solar cell design that applies a screen‐printed rear Al finger grid instead of the conventional full‐area aluminum (Al) rear layer while using the same PERC manufacturing sequence. We name this novel cell concept PERC+ because it offers several advantages. In particular, the Al paste consumption of the PERC+ cells is drastically reduced to 0.15 g instead of 1.6 g for the conventional PERC cells. The Al fingers create 2‐µm‐deeper aluminum back surface fields, which increases the open‐circuit voltage by 4 mV. The five‐busbar Al finger grid enables bifacial applications of the PERC+ cells with front‐side efficiencies up to 20.8% and rear‐side efficiencies up to 16.5% measured with a black chuck. The corresponding bifaciality is 79%. When applied in monofacial modules where the white back sheet acts as external rear reflector, the efficiency of the PERC+ cells is estimated to 20.9%, which is comparable with conventional PERC cells. Whereas Institute for Solar Energy Research Hamelin developed the aforementioned PERC+ results, SolarWorld independently pioneered a very similar bifacial PERC+ cell process starting in 2014. Transfer into mass production has been successfully accomplished, and novel glass–glass bifacial PERC+ modules have been launched at the Intersolar 2015 based on a most simple, lean, and cost‐effective bifacial cell process. These new bifacial PERC+ modules show an increase in annual energy yield between 5% and 25% in simulations, which is confirmed by first outdoor measurements. Copyright © 2015 John Wiley & Sons, Ltd.

Numerical investigations into the response of fabrics subjected to ballistic impact

The use of high-performance fibres for ballistic protection has made it possible to produce lightweight soft body armour. This provides more mobility and comfort to body armour users such as soldiers and police officers. Efforts to design more protective body armour at a reduced weight have ever continued. Ballistic impact modelling, which provides an in-depth understanding of the energy absorption mechanism of ballistic fabrics, plays an important role in designing lightweight soft body armour. This paper reports the results of numerical investigations into the stress distribution and failure mode of ballistic fabrics subjected to high-velocity impact. Finite-element (FE) models were built up and used to predict the response of ballistic fabric systems. The research confirmed that the fabric is able to absorb more impact energy with enhanced yarn–yarn friction, indicating that, if by special weaving techniques of yarn–yarn friction increase, an improvement in ballistic performance might be expected. It was also predicted from the FE simulation that yarn–yarn friction not only influence the projectile engagement time with the fabric, but also plays an important role in stress distribution on the primary and the secondary yarns. In addition, theoretical prediction from a multi-ply fabric system showed that the front layers of fabric are more likely to be broken in shear, and the rear layers of fabric tend to fail in tension. This suggested that using shear resistant materials for the front layer and tensile resistant materials for the rear layer may improve the ballistic performance of fabric panels.

Numerical and experimental investigations into ballistic performance of hybrid fabric panels

Strong, low density fibres have been favoured materials for ballistic protection, but the choice of fibres is limited for making body armour that is both protective and lightweight. In addition to developments of improved fibres, alternative approaches are required for creating more protective and lighter body armour. This paper reports on a study on hybrid fabric panels for ballistic protection. The Finite Element (FE) method was used to predict the response of different layers of fabric in a twelve-layer fabric model upon impact. It was found that the front layers of fabric are more likely to be broken in shear, and the rear layers of fabric tend to fail in tension. This suggested that using shear resistant materials for the front layer and tensile resistant materials for the rear layer may improve the ballistic performance of fabric panels. Two types of structure, ultra-high-molecular-weight polyethylene (UHMWPE) woven and unidirectional (UD) materials, were analyzed for their failure mode and response upon ballistic impact by using both FE and experimental methods. It was found that woven structures exhibit better shear resistance and UD structures gives better tensile resistance and wider transverse deflection upon ballistic impact. Two types of hybrid ballistic panels were designed from the fabrics. The experimental results showed that placing woven fabrics close to the impact face and UD material as the rear layers led to better ballistic performance than the panel constructed in the reverse sequence. It has also been found that the optimum ratio of woven to UD materials in the hybrid ballistic panel was 1:3. The improvement in ballistic protection of the hybrid fabric panels allows less material to be used, leading to lighter weight body armour.

Effects of Interpass Idle Time on Thermal Stresses in Multipass Multilayer Weld-Based Rapid Prototyping

Interpass idle time is an important parameter affecting the thermal stress distribution in weld-based rapid prototyping. In this paper, the effects of interpass idle time on thermal stresses in multipass multilayer weld-based rapid prototyping are investigated using numerical simulation. Meanwhile the single-layer weld-based rapid prototyping experiment is carried out, and the residual stresses are measured in the blind-hole method. The variation trend of calculated residual stresses agrees with that of experimental measurements. The research results indicate that there exist stress release effects of rear pass on fore passes and that of rear layer on fore layers. The interpass and interlayer stresses and residual stresses are significantly dependent on interpass idle time. The residual stresses of deposition workpiece decrease with the increase of interpass idle time, whereas the interpass and interlayer stresses on the central line of substrate increase with the increase of interpass idle time.

Infrared light management in high-efficiency silicon heterojunction and rear-passivated solar cells

Silicon heterojunction solar cells have record-high open-circuit voltages but suffer from reduced short-circuit currents due in large part to parasitic absorption in the amorphous silicon, transparent conductive oxide (TCO), and metal layers. We previously identified and quantified visible and ultraviolet parasitic absorption in heterojunctions; here, we extend the analysis to infrared light in heterojunction solar cells with efficiencies exceeding 20%. An extensive experimental investigation of the TCO layers indicates that the rear layer serves as a crucial electrical contact between amorphous silicon and the metal reflector. If very transparent and at least 150 nm thick, the rear TCO layer also maximizes infrared response. An optical model that combines a ray-tracing algorithm and a thin-film simulator reveals why: parallel-polarized light arriving at the rear surface at oblique incidence excites surface plasmons in the metal reflector, and this parasitic absorption in the metal can exceed the absorption in the TCO layer itself. Thick TCO layers—or dielectric layers, in rear-passivated diffused-junction silicon solar cells—reduce the penetration of the evanescent waves to the metal, thereby increasing internal reflectance at the rear surface. With an optimized rear TCO layer, the front TCO dominates the infrared losses in heterojunction solar cells. As its thickness and carrier density are constrained by anti-reflection and lateral conduction requirements, the front TCO can be improved only by increasing its electron mobility. Cell results attest to the power of TCO optimization: With a high-mobility front TCO and a 150-nm-thick, highly transparent rear ITO layer, we recently reported a 4-cm2 silicon heterojunction solar cell with an active-area short-circuit current density of nearly 39 mA/cm2 and a certified efficiency of over 22%.

SUSPENDED CEILING STRUCTURE AND LAYER-CORE-LAYER ACOUSTIC CEILING PANEL THEREFOR

An acoustic ceiling panel for a lay-in or suspended ceiling includes a core portion, and front and rear layers covering front and rear sides, respectively, of the core portion. The air flow resistance of the core portion does not exbeed about 100 MKS rayls. The air flow resistance of the front layer lies in the range of about 300 to about 800 MKS raylt The air flow resistance of the rear layer lies in the range of about 300 to about 1200 MXS rayls. The panel would be supported on a grid suspended belbw a structural ceiling to form an air space therebetweeu.

First demonstration of a Compton gamma imager based on silicon photomultipliers

We are developing a rugged and person-transportable Compton gamma imager for use in security investigations of radioactive materials, and for radiological incident remediation. The imager is composed of layers of scintillator with light collection for the forward layers provided by silicon photomultipliers and for the rear layer by photomultiplier tubes. As a first step, we have developed a 1/5th-scale demonstration unit of the final imager. We present the imaging performance of this demonstration unit for 137Cs at angles of up to 30° off-axis. Results are also presented for 113Sn and 22Na. This represents the first demonstration of the use of silicon photomultipliers as an embedded component for light collection in a Compton gamma imager.

Use of External Testing Methods to Assess Damage on Rockfall Protection Structures

This paper deals with the evaluation of damage due to boulder impact on rockfall protection embankment thanks to external methods. A 4 m high, 8 m long three layered structure is built using cells filled with different material according to their location in the structure. The structure is impacted by a 6500 kg spherical boulder with a maximal impact energy of 2000 kJ. The behaviour of the structure is first investigated using topographic surveys. Then, the results are compared with geophysical measurements. Results show that a low-energy impact leads to (i) the densification of both front and inner-layers associated with the swelling of the materials of the rear layer in the impact plane, and (ii) to the readjustment of internal materials which induces a local densification in a plane offset of 2 m. A high-energy impact induces large deformations on both inner and rear layers. These results are confirmed by seismic velocities which decrease with successive impacts.