Optimized spatial correlations for broadband light trapping nanopatterns in high efficiency ultrathin film a-Si:H solar cells

Nanophotonic structures have attracted attention for light trapping in solar cells with the potential to manage and direct light absorption on the nanoscale. While both randomly textured and nanophotonic structures have been investigated, the relationship between photocurrent and the spatial correlations of random or designed surfaces has been unclear. Here we systematically design pseudorandom arrays of nanostructures based on their power spectral density, and correlate the spatial frequencies with measured and simulated photocurrent. The integrated cell design consists of a patterned plasmonic back reflector and a nanostructured semiconductor top interface, which gives broadband and isotropic photocurrent enhancement.     

Resource checking and event handling within the W7-X segment control framework

ITER, Wendelstein 7-X, LHD, and TORE SUPRA are experimental facilities designed to lead the way to steady state fusion devices. These experiments require strategies to sustain a discharge in case of unforeseen events, e.g. heat overloads of plasma facing components or the failure of a plasma heating source. A recovery strategy is needed to get the discharge back for physics exploitation. For this purpose the W7-X segment control framework provides means for automated event detection along with options to formulate and initiate a recovery strategy. Besides handling of failures and degradation there are events that represent a desired plasma physical effect. An example for this kind of event is a transition to from Low to High-Confinement mode. These events indicate that a certain plasma state is reached and scientific examination can be altered thus enabling event-driven multiple experiments per discharge. Examples of both kinds of events will be presented and compared to other approaches in the community.     

Enhanced densification of Ti–6Al–4V powders by transformation-mismatch plasticity

The densification kinetics of Ti–6Al–4V powders with spherical or angular shapes are compared in uniaxial die pressing experiments between isothermal conditions (at 1020 °C, in the β-field, where deformation occurs by creep) and thermal cycling (between 860 and 1020 °C, within the range of the α–β phase transformation of the alloy, where transformation-mismatch plasticity is activated). Densification kinetics are only moderately affected by powder shape, but are markedly faster under thermal cycling than under isothermal conditions, as expected from the higher deformation rate achieved under transformation-mismatch plasticity conditions as compared to creep conditions. The densification curves for both creep and mismatch plasticity deformation mechanisms are successfully modeled for various applied stresses and for partial cycling, when transformation is incomplete. Tensile properties of specimens fully densified under thermal cycling conditions are similar to literature values from Ti–6Al–4V densified by isothermal hot isostatic pressing.     

Comparison of test protocols for the standard room/corner test

As part of international efforts to evaluate alternative reaction‐to‐fire tests, several series of room/corner tests have been conducted. Materials tested were mostly different wood products but included gypsum board and a few foam plastics. This is a review of the overall results of related studies in which the different test protocols for the standard room/corner test were used. Differences in the test protocols involved two options for the ignition burner scenario and whether or not the ceiling was also lined with the test materials. The test materials were placed on three walls of the room in all the tests. The two burner scenarios were (1) 40 kW for 300 s followed by 160 kW for 300 s and (2) 100 kW for 600 s and 300 kW for 600 s. The 40 and 160 kW burner scenario without the ceiling lined did not provide a severe enough test for flashover to occur with fire‐retardant‐treated materials. Use of the 100 and 300 kW burner scenario without lining the ceiling provided the ability to differentiate between wood products with ASTM E 84 flame spread indexes of 70 to 125 and those with higher flame spread indexes. Lining the ceiling with test material creates a more severe test.     

A Finite Element Approach to Modeling Abrasive Wear Modes

Machine components operating in sandy environments will wear because of the abrasive interaction with sand particles. In this work, a method is derived to predict the amount of wear caused by such abrasive action, in order to improve the maintenance concept of the components. A finite element model is used to simulate various tips scratching a smooth surface. The model is verified by comparing the obtained results with a set of experiments performed earlier (M. Woldman, et al., 2013, Wear, 301(1–2), pp 76–81).     

A new method for predicting Forming Limit Curves from mechanical properties

Forming Limit Curves (FLCs) are an important tool in steel sheet metal forming. Experimental measurements of FLCs are costly, and therefore, empirical prediction methods are of practical use. Difficulties in accurately defining FLCs for new steel grades, such as AHSS, have necessitated a review of the existing prediction methods. Four points were defined to characterise an FLC, and correlations between the coordinates of these points and the mechanical properties from tensile testing were found. The results show that the total elongation, Lankford coefficient and thickness are strongly related to the FLC values. Predictive equations were derived from the statistical relations between the measured FLC points and the mechanical properties. To verify the predictive equations, predicted FLCs for approximately fifty steel grades in various thickness ranges were compared with measured FLCs. It was found that the newly developed method accurately predicts the FLCs.     

An anisotropic stress based criterion to predict the formability and the fracture mechanism of textured zinc sheets

The Forming Limit Diagram (FLD) of a textured zinc sheet has been identified via tensile and bulge tests. The strong anisotropy of the sheet is reflected in the tensile tests, and even more strikingly in the formability measured from the bulge tests. The dependence of the FLD on the orientation of the sheet is unusual, and is shown to be well captured by an anisotropic stress based criterion. The criterion is also able to predict the observed cracks orientations.     

Three Nb single crystals processed by equal-channel angular pressing—Part I: Dislocation substructure

Three high-purity Nb single crystals with different orientations are deformed by equal-channel angular pressing (ECAP) at room temperature for one pass. The microstructures of two different cross-sections are systematically characterized by means of electron backscatter diffraction on various length scales. The completely different microstructural features of the three single crystals provide clear experimental evidence that crystallographic orientation has a strong influence on orientation splitting and on microstructural heterogeneity. Lattice rotation is analyzed by comparing the crystal orientation before and after ECAP. The orientation evolution reveals that the three crystals tend to align in such a way that the primary slip plane and the primary slip direction overlap with the simple shear plane and direction, respectively. An in-depth analysis of the large misorientation bands is given in a companion paper.     

Anisotropic mechanical behavior and formability criterion for zinc sheets

The mechanical behavior of zinc has been studied and linked to the formability of sheets. An anisotropic elastic–viscoplastic behavior law has been developed to take into account the anisotropy of the material. Anisotropy is induced by crystallographic and morphological textures, and possibly by the spatial distribution of intermetallics. The temperature dependence is introduced through a Zener–Hollomon type term. The resulting anisotropic formability of sheets implies a new approach by adapting the forming limit diagram with a stress based criterion. This approach is confronted and validated by considering the industrial forming of a head clip.