Impact Of Surface Conditions Research Articles

Laser Direct Joining of Steel to Polymethylmethacrylate: The Influence of Process Parameters and Surface Mechanical Pre-Treatment on the Joint Strength and Quality.

The search for lightweight structures increases the demand for non-metallic materials, such as polymers, composites, and hybrid structures. This work presents the dissimilar joining through direct laser joining between polymethylmethacrylate (PMMA) and S235 galvanised steel using a pulsed Nd:YAG laser. The main goal is to determine the influence of processing parameters on joint strength and quality. In addition, the impact of surface conditions on the joint quality was also analysed. Overall, the optimum ranges of process parameters were found, and some are worth highlighting, such as the laser beam diameter and pulse duration, which significantly influenced the joint strength. Failure of the welded samples occurred in PMMA component, demonstrating good joint efficiency. Additionally, a maximum increase of 5.1% of the tensile shear strength was achieved thanks to the mechanical pre-treatment. It is possible to conclude that the joining between PMMA and the S235 galvanised steel can be performed by optimising the process parameters. Additionally, it can be enhanced through surface pre-treatments by exploring the mechanical interlock between both materials.

Impact of surface condition and roughness on sediment formation: an experimental sewer system operated with real wastewater.

Regular sewer cleaning in North Rhine-Westphalia (Germany) generates annual costs of around 50 million Euros. This leads to the question of whether and to what extent sewer cleaning is necessary. To determine the effect of roughness, sewer surface condition and discharge, experiments with real wastewater were performed, using a sewer test track with acrylic glass tubes (DN 300) prepared with abrasive paper and nature stone tiles at the wastewater treatment plant (WWTP) Bochum-Ölbachtal (Ruhrverband, Germany). A logarithmic relationship between deposit height and time was found to lead to maximum deposit heights of 5 to 60 mm. Surface structure analysis by texture measuring indicated that deposits within the first 28 days after cleaning are highly influenced by the surface condition of the sewer and not necessarily by roughness. Furthermore, under dry weather conditions deposit heights are nearly stable after this time, indicating the limiting effect of sewer cleaning. Deposit formation amounted to 1.75-1.80 mm/d at a roughness of ks = 0.10 mm (fine but catchy microstructure) and 0-0.1 mm/d at ks 1.25 mm (wavy microstructure) at steady state and transient discharge within the first 28 days after sewer cleaning.

Ozone-based Surface Conditioning Focused on an Improved Passivation for Silicon Heterojunction Solar Cells

Silicon Heterojunction (SHJ) solar cells represent a key technology to approach very high conversion efficiencies close to the theoretical limit of silicon solar cells. The main advantages of SHJ solar cells are a lean production chain with low temperature processes and the passivating hetero-structure contact which simultaneously fulfils the passivation and contacting role. For an improved passivation a smooth and low-defect concentration surface is required.This paper focuses on a new simple, cost effective and production-feasible ozone-based surface conditioning process for the controlled rounding and smoothing of textured surfaces applied in SHJ solar cells. The impact of surface conditioning on optical and morphological properties is analyzed for alkaline textured surfaces with small to medium and large size pyramids by reflection measurements and high resolution imaging methods as scanning electron microscopy (SEM) and atomic force microscopy (AFM).

Impact of Surface Conditions on the Superconductivity of Si(111)-(√7 × √3)-In

We performed low-temperature scanning tunneling microscopy and spectroscopy on Si(111)-( √ 7× √ 3)-In in magnetic fields. Superconducting vortices were observed by mapping zero-bias conductance in an area consisting of flat terraces separated by atomic steps. While vortices in the terrace regions have an isotropic shape with a normal-state core, those at the atomic steps have anisotropic shapes and the superconductivity is only weakly suppressed in the cores. These properties are understood as a crossover from a normal vortex to a Josephson vortex. We conclude that the atomic steps work as Josephson junctions limiting the density of supercurrents. [DOI: 10.1380/ejssnt.2015.151]

Impact of surface condition on sulphide stress corrosion cracking of 316L stainless steel

The effect of surface condition on crack initiation in 316L stainless steel during laboratory testing in sour (H2S) environments for oil and gas applications has been investigated using the four-point bend test method. The main focus was on the effect of the degree of surface damage introduced during specimen machining and the influence of heat tinting to simulate the welding process. Detailed mapping of the surface of the four-point bend specimens before and after the tests revealed a greater tendency for pits to form at pre-existing mechanical defects than at inclusions. Perhaps surprisingly, pitting was initiated more readily on the finer ground surface. The effect of heat tinting was (i) to increase the pit density and (ii) to facilitate cracking, shifting the material from the pass to the failure domain. In all cases cracks initiated at pitting sites. A clear time dependence was observed in both the evolution of pitting and the transition from pit to crack during the four-point bend test, implying that the standard 30day test duration may not always be sufficiently conservative. Characterisation of pitting and cracking in the specimens using electron back-scatter diffraction (EBSD) and focused ion beam (FIB) milling revealed evidence of de-alloying local to the crack. The origin of the cracks could not be identified precisely but initiation in the thinned region of the metal caused by undercutting or intense localised dissolution along slip bands could both be important. Comparison of residual stress measurement using X-ray diffraction (XRD) and hole-drilling techniques demonstrated that near-surface residual stress measurement in austenitic stainless steels using XRD should be treated with caution due to the presence of a heavily deformed nanocrystalline layer on the surface arising from the machining process.

Winter variability of aeolian sediment transport threshold on a cold-climate dune

Changes in surface conditions on cold-climate aeolian dunes are pronounced; during winter dunes are wet, snow covered, and/or frozen for extended periods of time. It is unknown how the critical wind speed for sediment transport (“threshold”) varies and how threshold may influence sediment transport predictions. Although the impact of surface conditions on threshold has been examined in synthetic experiments (wind tunnels), complicated feedbacks between threshold, sand transport, and surface conditions that occur in natural environments suggest that a ground-based empirical approach may provide enhanced insight. In this study we investigate threshold variability for 73days during fall–winter–spring surface conditions from 18 November 2008 to 30 May 2009 in the Bigstick Sand Hills of Saskatchewan, Canada. Simultaneous measurements of threshold and atmospheric variables (air temperature, relative humidity, solar radiation, wind speed and direction) were used to examine the extent to which surface erodibility was regulated by meteorology. Time‐lapse images of the surface from a co-located camera were used for quality control and interpreting changes in the surface affecting threshold. Results reveal that threshold varied throughout the deployment (25–75% quartiles: 6.92–8.28ms−1; mean: 7.79ms−1). Threshold variability was especially evident at two scales: (i) event timescale and (ii) seasonal timescale. Event-scale variability peaked during mid-winter; in one event the threshold varied by 6ms−1 in 2h with freezing and re-freezing of the surface and relatively constant atmospheric conditions. The causes of event-scale variability are complex though qualitatively related to changes of wind direction, antecedent meteorological conditions, and vertical variations of grain-scale bonding agents such as pore ice and moisture. Seasonal-scale changes manifested as an increase in threshold during fall, peaking in mid-winter, and decreasing in spring. Increased threshold in mid-winter was linked to lower insolation and air temperature, suggesting low erodibility due to the presence of pore ice. Correlation coefficients of threshold versus atmospheric variables yielded relatively weak correlations (air temperature: r=−0.322; relative humidity: r=0.388; solar radiation: r=−0.309) that also varied according to wind direction, suggesting that the link between atmospheric conditions and surface erodibility on cold‐climate dunes is complex. This contrasts with results from field-based studies in warmer climates and controlled wind tunnel experiments, which show a more direct link between atmospheric variables (temperature and humidity) and surface erodibility. Nevertheless, our results do show a seasonal pattern of threshold that could be important for modeling cold-climate aeolian sediment transport.

Impact of surface conditions on thin sea ice concentration estimate from passive microwave observations

Ice concentration retrieved from spaceborne passive microwave observations is a prime input to operational sea ice monitoring programs, numerical weather prediction and global climate models. However, it is usually underestimated by existing algorithms due to surface conditions, especially in case of young ice types. Evaluation of those algorithms identifies errors in concentration estimates but does not necessarily link them to the adverse surface conditions. The present study is an attempt to establish those links for young ice (<25cm) thick. It uses measurements of microwave emission from artificially grown sea ice in an outdoor tank and calculates ice concentration using five established algorithms: NT, Bootstrap (BSA), NT2, ASI and ECICE. Since the actual concentration is known (100%), then any deviation from this value is considered an error and can be linked to the observed surface conditions, which are usually caused by weather events. Those conditions were acquired on hourly or daily basis. Results identify key conditions that lead to underestimation of ice concentration. They include surface refreezing, slush, snow settling following fresh snowfall, and falling precipitation in different forms. The study shows also that NT and NT2 are most affected by surface processes while BSA performs better. ASI is much less affected because it uses the high frequency channel (e.g. SSM/I 85GHz), which is sensitive only to processes within the top snow layer. ECICE, with its probabilistic and ensemble approach shows also good results under most surface conditions. Dry or wet snow does not lead to significant difference in ice concentration estimate. The study also aims at validation of ECICE.

EXAMINATION OF ROUGH SURFACES WITH EDDY CURRENT METHOD

As the relationship between some important parameters of materials and their electric conductivity really exists, it makes it possible to use the eddy current method to measure conductivity of material in a non-destructive manner and then infer about the desired properties of materials, their continuous or non-continuous structure or some geometrical parameters. However, the substantial impact of surface condition demonstrated by examined materials onto test results is a significant drawback of the eddy current method. This is why, a new and innovative method for compensation of material surface roughness onto results of conductance measurements is proposed. The presented method is based on the double calibration process applied to the measuring kit of the conductometer and the measuring probe.

The impact of surface conditioning and area on the pulsed breakdown strength of water

Experimental results are presented on the degree to which electrode surface conditioning and surface area impact the dielectric strength of water. The applied pulse to the test gap reached electric field levels greater than 1.5 MV/cm with risetimes around 200 and 50 ns, respectively. The test gap is composed of 304 stainless steel electrodes machined with a Bruce profile. Electrode surface roughness ranged from 0.34 to 1.41 /spl mu/m and effective areas ranged from 0.5 to 75 cm/sup 2/. Additional results are presented on the pulsed breakdown strength of Rexolite with various surface finishes ranging from .025 to 5.715 /spl mu/m. Conclusions are made as to the effect electrode surface area and surface roughness has on the holdoff voltage of water dielectric systems. Conclusions are also made as to the impact of the surface condition of Rexolite has on its bulk breakdown strength.