Double Passes Research Articles

Experimental investigation on characterization of friction stir processed AZ31-based composite

Present study has been conducted to characterize the Mg alloy namely AZ31-based composite joined by Friction stir processing (FSP) technique. This study deals with the effect of single and double passes in FSP of AZ31 Mg alloy. The single pass run in FSP is followed at tool rotation speed (N) of 1000 to 1400 rpm. Also, the double pass run in FSP was followed at these speeds without using reinforcements. The feedstock particles namely SiC, Al2O3, Cr, and Si powders were used in fabrication process. The hardness, impact strength, and tensile strength characteristics were assessed in the stir region zone, and the results indicated significant improvement in these properties. The highest values of mechanical strength were seen in the FSPed area with N = 1000 rpm at a constant transverse speed (r) of 40 mm/min. Also, the tensile strength of the two passes FSPed plates is much higher than that of the single section without any reinforcement, as revealed in previous study also. The Scanning electron microscopy (SEM) analysis is done at two different magnifications for the Silicon carbide, Alumina, Chromium, and Silicon powder reinforced composites fabricated at speed of 1000 rpm. The microstructure shows that reinforced particles were uniform dispersed into FSPed region and agglomerated with Mg matrix. Si powder produces finer microstructure as compare to SiC, Al2O3, Cr. FSP decreases the grain size of processed material. Optical Microscopy results revealed that the reinforcement particle produced a homogenous microstructure and, a refined grain and equally dispersed in matrix material without split to the particle.

Effect of equal channel angular pressing on strain deformation behavior of ultrafine grained during low temperature superplasticity of AA5083

AA5083 with ultrafine grain structure was produced through equal channel angular pressing using different levels of ECAP tensions, underwent a series of tensile tests. The superplasticity temperature 573 K at low temperatures. This study investigate how varying the ECAP strain influences the distinctive microstructure of the alloy and its impact on deformation mechanisms within the low-temperature superplasticity range. A fraction of the high angle borders increased when the equal channel angular pressing strain was increased from 1 to 2, while the sub-grain size stayed nearly same. This was the most applicable microstructural evolution. After double passes, the material showed superplastic elongations, but after single pass, it did not show low temperature superplasticity. Upon analyzing the mechanical data using typical deformation mechanisms, it was determined that dislocation climb controlled the samples deformation after the first pass, whereas grain boundary sliding was responsible for the sample's low temperature superplasticity after the second pass. In the present study, we explored the differences in deformation mechanisms by considering the microstructures formed under various ECAP strains. Equal channel angular pressing with a BC route and an effective strain of 1∼2, we created an ultrafine-grained AA5083. A significant increase was seen in the fraction of particles measuring 1.8–3.8 μm under the current ECAP conditions. The implementation of equal channel angular pressing, there was a significant increase in the occurrence of voids with sizes ranging from 0.8 to 1.8 μm. According to the current analysis and results, if moderate superplastic elongation is guaranteed, it may be preferable to have fewer equal channel angular pressing passes than those that result in the largest elongation while taking into account cavitation damage and the low temperature superplasticity of ultrafine grained AA5083 used in commercial applications.

On reinforcing the friction stir weld joints of AA5086-H116 using the plasma spray coatings

The fatigue properties of friction stir weld joints of AA5086-H116 alloy, reinforced with Al2O3 particles using the plasma spray coating method, were investigated after single and double weld passes. A relatively uniform distribution of reinforced particles was achieved with superior properties, even higher than that of the parent alloy. The reinforced joints had enhanced hardness as well as joint efficiency, the double pass being superior to the single pass, but at the cost of reduced total elongation. Furthermore, the reinforced double-pass joints exhibited a remarkable ∼ 55%, ∼ 14%, and ∼ 89% increase in fatigue strength compared to the as-weld, the base material, and single-pass joints, respectively. The fractographic examination mainly revealed a defect-free crack initiation mechanism with a few cases of the ones induced by defects. The superior fatigue performance was mainly attributed to the uniform spatial and size distribution of fine Al2O3 particles within the weld nugget zone, thanks to the novel weld reinforcement method used in this study, which provides a promising avenue for improving the fatigue properties of weld joints.

Flow Behavior and Mechanical Properties of Multi-Pass Thermomechanically Processed 7075 Al-Alloy

Research on multi-pass hot processing of 7075 Al-alloy was rarely discussed. This study aims to design and evaluate different thermomechanical processing strategies (TMPS) to produce 3 mm-thick sheets of 7075 Al-alloy. A physical simulation was performed using the hot compression test of a Gleeble 3500 to study flow mechanisms and microstructural evolution, while an experimental investigation was carried out using a rolling mill to examine the effect of TMPS on the mechanical properties. Four hot forming strategies were designed and tested at a constant strain rate of 0.1 s−1 over a temperature range of 200–450 °C. These strategies involved applying a constant amount of deformation of 65–70% in single (SP), double (DP), triple (TP), and quadruple (QP) passes of thermomechanical processing to study the influence of multi-pass thermomechanical processing on the final mechanical properties and industrial feasibility. The microstructure analysis showed a significant refinement and more uniform distribution of precipitates with an increasing number of passes, as observed through optical micrographs and the full width at half maximum (FWHM)-position relationship of XRD data. The results indicate that QP is the optimum strategy for producing the best mechanical properties in the shortest production time.

Monitoring of insect pests using GIS applied to the Oryza sativa L. crop in Naranjal, Ecuador

In Ecuador, the cultivation of rice (Oryza sativa L) is affected by various insect pests that cause the deterioration of the vegetation. Therefore, this problem was investigated in the Canton Naranjal in four rice farms covering a total area of 213.8 ha, carrying out "X" sampling with 20 double passes with the entomological net. Geographic Information Systems (GIS) tools were used to geo-reference the insects that prevail in the crop and at the same time observe the locations and know in which phenological stage they are present with the assistance of the BBCH Codification. Thematic maps of pest and beneficial insects were made with Density Kernel allowing the population of insects per m² found in the three samplings to be estimated. The percentages vary by phenological stage, but five pest insects predominate: Hydrellia sp, Tagosodes oryzicolus Müir, Rupella albinella, Oebalus ornatus (Adult), Tibraca limbativentris (Adult - Nymph), the GIS allow a spatial distribution of the pest insects.

Dome seeing analysis of the Anglo-Australian Telescope

Dome seeing is an often overlooked avenue for seeing improvement for a telescope. Because most existing telescope domes have not been characterized for turbulence, there is an opportunity to improve the overall seeing by minimizing the dome contribution, thereby optimizing scientific productivity and operations. A dome turbulence sensor has recorded data in the Anglo-Australian Telescope (AAT) over the past year. The instrument consists of a collimated laser beam that propagates (and double passes) between the AAT’s primary mirror box and a flat mirror on the secondary strut. The angle-of-arrival fluctuations are used to derive a dome-seeing-proxy in arcsec. We found the dominant effects to be the temperature gradients and wind speed. Convection conditions are considerably more detrimental to the dome-seeing-proxy than thermal inversion conditions. Unlike other large telescopes, there is no discernible relationship between the dome-seeing-proxy and relative wind direction. Concerning telescope operations, it would be worth considering lowering the air-conditioning set point temperature to include a higher proportion of observations under thermal inversion. Nevertheless, this must be carefully weighed with the risk of condensation in the dome, a major concern for a site with frequent high relative humidity.

Substantiation of the Line for the Primary Processing of Industrial Hemp lnto Hemp of the Same Type Undirected

It was shown that there is a need for the research and development of domestic lines for processing two-season raw industrial hemp of autumn and spring harvesting. The lines need to be efficient, low-cost and produce fiber of various qualities.Research purpose The research aimed to substantiate the design of a low-cost line for the primary processing of technical hemp harvested in autumn and spring as a tangled mass of broken stems, and work out the recommendations for processing raw materials.Materials and methods Autumn harvest hemp was processed in four ways: single, double, triple and quadruple pass through the flax line of primary processing, without changing the settings of the machines. The design of this line was detailed as follows: DLV-2 flax disintegrator, horizontal lamellar fiber unloader of the VUL system named after I.N. Levitsky and two shaking machines with a lower combed field at the rotation frequency of a disintegrator rotor of 1000 revolutions per minute, and a swing frequency of the shaking machine needle rollers of 230 revolutions per minute. The obtained hemp was examined for quality indicators according to the current standards.Results and discussion It was revealed that the medium length of broken stems is 150 millimeters, the minimum and maximum length varies from 24 to 485 millimeters. It was shown that autumn harvest hemp is difficult to process: single and double passes of autumn harvest hemp through the line under research do not provide the desired fiber quality, which does not correspond to even the lowest grade. The third pass revealed to be possible to provide a quality fiber, and the fourth proved to be impractical.Conclusions It was proved that the separation and breaking load of the fiber in autumn harvest hemp weed differ from spring harvest hemp: 4.6 units versus 8.2-8.6 and 9.3 kilogram-force versus 13.5-16.9, respectively. The authors determined the quality indicators of hemp of the same type, undirected, and its yield with various processing options. For the first time, a domestic line for processing autumn and spring hemp with a capacity of 600 kilograms per hour and more was proposed, which allows to change the fiber quality, get a 1.5-2.0 times increase in productivity and change the fiber cost. The recommendations were substantiated for the effective hemp processing and the necessity of creating a disintegrator for hemp.

Processability and cracking behaviour of novel high-alloyed tool steels processed by Laser Powder Bed Fusion

Concerning tooling applications, Laser Powder Bed Fusion (LPBF) enables new features such as internal cooling channels that can be implemented in cutting or shaping tools. Thus, higher cutting speeds are feasible thanks to the more efficient cooling that could not be obtained by channels fabricated with conventional methods. However, the alloys exploited for the cutting tools production usually contain high levels of carbon, which makes their LPBF processability challenging due to their high crack-susceptibility. In this work, an approach based on the use of basic physical/empirical indicators has been employed to map the processability of six novel high-alloyed tool steel grades. A large experimental campaign with variable energy densities, single and double passes, as well as different focal points was designed. The results exhibit highly dense but cracked parts. In particular, the LPBF processability deteriorates with increasing carbon content, suggesting that mostly chemistry, rather than process parameters, plays a key role in the determination of the LPBF feasibility. The cooling rate, cooling time between 800 °C and 500 °C, equivalent carbon content, solidification interval, martensite start temperature and volumetric energy density were employed as indicators to provide a rapid classification of processability. The work demonstrates that the combined use of the indicators can better explain the cracking behaviour of carbon-containing tool steels. At a screening level, this approach based on complementar use of physical/empirical tools, may significantly shorten the experimental effort during the design of new compositions, especially when dealing with crack susceptible alloys like carbon-containing tool steels.

Influence of Friction Stir Process on the Physical, Microstructural, Corrosive, and Electrical Properties of an Al-Mg Alloy Modified with Ti-B Additives.

In this study, two successive methods were used to improve the grain structure and the mechanical and physical properties of Al 5052 aluminum alloy. The modifying elements, 0.99 wt.% of titanium (Ti) and 0.2 wt.% of boron (B), were added during the casting process. After solidification, single- and double-pass friction stir processing (FSP) were performed to achieve additional grain refinement and disperse the newly formed phases well. The addition of Ti–B modifiers significantly improved the mechanical and physical properties of the Al 5052 aluminum alloy. Nevertheless, only a 3% improvement in microhardness was achieved. The ultimate strength (US), yield strength (YS), and elastic modulus were investigated. In addition, the electrical conductivity was reduced by 56% compared to the base alloys. The effects of grain refinement on thermal expansion and corrosion rate were studied; the modified alloy with Ti–B in the as-cast state showed lower dimension stability than the samples treated with the FSP method. The grain refinement significantly affected the corrosion resistance; for example, single and double FSP passes reduced the corrosion rate by 11.4 times and 19.2 times, respectively. The successive FSP passes, resulting in a non-porous structure, increased the bulk density and formed precipitates with high bulk density.

Reflow Residues on Printed Circuit Board Assemblies and Interaction With Humidity

Ionic residues resulting from the soldering process is an important parameter in connection with humidity robustness of Printed Circuit Board Assemblies (PCBAs) due to their ability to enhance moisture absorption and surface conductivity. For reflow process, residues are trapped under the components, and the morphology of the residues can change with humidity exposure resulting in the release of ionic components. In this work, trapped residues below the components from reflow process of several commercial PCBAs were characterized before and after exposure to humidity conditions. PCBAs used for the analysis had undergone multiple reflow heating profiles by single and double reflow plus additional passes to understand heating effects. The morphology change of the trapped residues under components upon humidity exposure was observed using optical and scanning electron microscopy. The conductivity of the localized extracted solutions was measured and NaCl equivalency was determined. The solder paste materials were analysed for their water sorption property, while the effect of humidity on electrical property was assessed using electrochemical impedance spectroscopy using test PCBs. The results show that the change in morphology and level of activator release of residues were a function of the flux type, PCBA characteristics such as component standoff height and number of reflow cycles. Water layer formation upon humidity exposure and electrical properties on test PCBs are correlated with water sorption of the flux part.

Influence of hybrid pin profile on microstructural and mechanical properties of Al/SiC graded composites produced by friction stir processing

Friction stir processing (FSP) was employed to fabricate a surface graded composite by embedding SiC reinforcement particles in an AA6082-T6 matrix. Conical blind holes were drilled on the surface of the plate with varying inter-hole distances. The processing was performed with the different number of passes by keeping rotational and traverse speed constant. A new hybrid tool with a combination of conventional conical threaded tool and the triangular cross-sectioned tool was used in processing. The microstructural features of the processed samples were examined by a 3D microscope and scanning electron microscope (SEM). Mechanical properties such as microhardness, tensile strength was thoroughly evaluated. It is reported that the number of passes played an essential role in the distribution of reinforcement particles and grain refinement. The hardness value improved by applying multiple passes. The fractured tensile samples showed ductile failure. The sample treated with double passes gave better results with the homogenous distribution of reinforcement particles compared to samples processed with a single pass.

Energy, exergy, and economic analysis of tubular solar air heater with porous material: An experimental study

• Solar air heater having new designed tubular absorber is examined experimentally. • Assessment of the new tubular air heater with porous medium is presented. • Using porous material with tubular heater enhances its energy efficiency by 8.9% • Using porous media with tubular heater enhances its exergy efficiency by 8.2% • Tubular air heater is more effective compared to flat one based 4E analyses. The performance of solar air heater of having a new design tubular absorber of adjacent parallel tubes called tubular is investigated experimentally via energy, exergy, energy payback time, exergoeconomic, and enviroeconomic approaches. Moreover, the impact of utilizing porous material on the tubular heat performance is analyzed and compared to flat plate air heater at air mass flow rates; 0.075, 0.05, and 0.025 kg/s for single and double passes. Results indicate that the tubular heater has higher net energy gain, output air temperature, energy and exergy efficiencies, and smaller energy loss compared to the flat heater. Using porous material and double pass increases the output air temperature of tubular air heater by 3.4 °C and flat one by 17.7 °C at 0.025 kg/s. Moreover, utilizing porous material with the tubular heater at 0.075 kg/s enhances the energy efficiency by 3.5% and 8.9% and exergy efficiency by 8.2% and 0.9% for single and double pass, respectively. Air pumping power of the tubular heater is greater than flat but its value is very small to influence the tubular net useful energy. Finally, the tubular air heater is more effective compared to flat based on energy payback time, energy cost, exergoeconomic, and enviroeconomic parameters.

Effect of number of welding passes on the microstructure, mechanical and intergranular corrosion properties of 409M ferritic stainless steel

PurposeThis paper aims to study the effect of number of welding passes on microstructure, mechanical and corrosion properties of 409 M ferritic stainless steel. Shielded metal arc welding (SMAW) process is used to weld two metal sheets of 409 M having 3 mm thickness as bead-on-plate with single, double and triple passes. Microstructures were observed at transverse section with the help of optical microscope and with increasing number of passes grain growth, and the width of heat-affected zone (HAZ) increases. The results of tensile tests revealed that as number of passes increases, there is reduction in tensile strength and ductility. Double loop electrochemical potentiokinetic reactivation (DL-EPR) test revealed that as number of passes increases, the degree of sensitization increases. This is due to the deposition of chromium carbides at the grain boundaries and the associated depletion of chromium.Design/methodology/approachThree welded plates of single, double and triple pass were welded by SMAW process. From three welded plates (single, double and triple passes), samples for microstructural examination were cut in transverse direction (perpendicular to welding direction) with the help of wire-cut electrical discharge machine (EDM). The welded plates were sliced using wire-cut EDM along transverse direction for preparing optical microscopy, tensile testing, microhardness and DL-EPR testing specimens.FindingsFrom the microstructure, it was observed that the large grain growth, which is dendritic, and the structure become finer to increase in number of welding passes. As number of passes increases, the width of HAZ increases because of the higher temperature at the welded zone. The tensile strength decreases to increase the number of welding passes because of grain coarsening and chromium carbide precipitation in sensitized zone and wider HAZ. The maximum microhardness value was observed for single-pass weld as compared to double- and triple-pass welds because of the fast cooling rate. The degree of sensitization increases to increase the number of passes because of chromium carbide deposition at the grain boundaries.Originality/valueThe authors declare that the manuscript is original and not published elsewhere, and there is no conflict of interest to publish this manuscript.

Computational and statistical analysis on the U‐tube heat exchanger with different passes configuration: Taguchi method

AbstractIn the present study, the passive technique of heat transfer in which single pass and double passes are included in a simple U‐tube heat exchanger is analyzed. The computational fluid dynamics (CFD)‐based parametric analysis is carried out to optimize the parameters affecting the temperature drop and heat transfer achieved from the U‐tube heat exchanger. ANSYS Fluentv20 is used for the CFD analysis, and the RNG k‐ɛ model and energy equation were considered to define the turbulence and heat transfer phenomena. The Taguchi method is used to formulate the experimental work and analyze the working parameters of the U‐tube heat exchanger, such as hot and cold mass flow rate and hoRenew Energyt inlet temperature and cold inlet temperature. For the U‐tube heat exchanger, four operating parameters are considered at four different levels in the Taguchi method. The best combination of parameters for achieving a maximum temperature drop is A4B1C2D3, and it is A3B4C1D2 in case of heat transfer. A U‐tube single‐pass heat exchanger is more effective as compared with other U‐tube heat exchangers (zero‐ and double‐pass). Experimental results are provided to validate the suitability of the purpose of the approach.

Thermal Efficiency for Passive Solar Chimney with and Without Heat Storage material

In this study, a different design of passive air Solar Chimney(SC)was tested by installing it in the south wall of insulated test room in Baghdad city. The SC was designed from vertical and inclined parts connected serially together, the vertical SC (first part) has a single pass and Thermal Energy Storage Box Collector (TESB (refined paraffin wax as Phase Change Material(PCM)-Copper Foam Matrix(CFM))), while the inclined SC was designed in single pass, double passes and double pass with TESB (semi refined paraffin wax with copper foam matrix) with selective working angle ((30o, 45o and 60o). A computational model was employed and solved by Finite Volume Method (FVM) to simulate the air induced through the test room by SC effect. The governing equation of Computational Fluid Dynamic (CFD) model was developed by the effective heat capacity method equation to describe the heat storage and release from PCM-CFM. Practical and computational Results referred to increase in thermal conductivity of the paraffin wax that supported by CFM than 10 times, while the ventilation effect is still active for hours after sun set amount. The maximum ventilation mass flow rate with TESB collector was 36.651 kg/hr., when the overall discharge coefficient equals 0.371. Also, the experimental results referred to the best working angle range 45~60o, while the highest approaching temperature (between air and collector) was appeared for the double passes flat plate collector. Results gave higher heat storage efficiency 47% when the maximum solar radiation 780 W/m2 at 12.00 pm, and the energy summation through duration of charging time was 18460 kJ. Double passes SC at 60o angle presented the highest efficiency with value approaching to 73%, while TESB collector efficiency depicted highest efficiency value 70% at 12:00 pm.

Influences of 17-4PH Stainless Steel and α + β Titanium Alloy Powders for Corrosion Susceptibility on Friction Stir-Processed AA7075-T651 Aluminium Matrix Composites

Stainless steel (17-4PH) and α + β titanium alloy (Ti–6Al–2Sn–2Zr–2Mo–2Cr–0.25Si) powders have been known for their high strength with low density as well as promising mechanical properties and remarkable corrosion resistance. In view of this, a comparative performance assessment was carried out to evaluate their percentage inhibition performance efficiencies (%IPEs) on the friction stir-processed 7075-T651 aluminium matrix composites (AMC) reinforced with 17-4PH and Ti–6Al–2Sn–2Zr–2Mo–2Cr–0.25Si powders. The process parameters used were the plunge depth of 0.3 mm, processing speed of 20 mm/min, the tilt angle of 3°, the rotational speed of 1500 rpm and 100% inter-pass overlap with double passes. Corrosion study was carried out in a concentration of 3.5% NaCl medium at an ambient temperature of 25 °C using potentiodynamic polarization technique on AA7075-T651/17-4PH AMC and AA7075-T651/Ti–6Al–2Sn–2Zr–2Mo–2Cr–0.25Si AMC with reference to the processed and unprocessed base metal. It was revealed that the AA7075-T651/Ti–6Al–2Sn–2Zr–2Mo–2Cr–0.25Si AMC has higher %IPE of 98.26%, while AA7075-T651/17-4PH AMC exhibited %IPE of 90.57%. The corrosion rate was extraordinarily reduced from 5.0718 to 0.087675 mm/year using α + β titanium alloy powder as corrosion resistance while that of 17-4PH stainless steel reduced to 0.47744 mm/year. The polarization resistance was greatly high when inhibition α + β titanium alloy powder was used and found to be 2240.7 Ω as against 191.06 Ω when 17-4PH stainless steel was used as a corrosion barrier. The SEM images of the corroded samples revealed the presences of pits and intergranular corrosion attack with the trace of flakes on the surfaces.

Transient Behavior Analysis for Solar Energy Storage in PCM-CFM Material Using Equivalent Heat Capacity Method as Storage Model

A paraffin wax and copper foam matrix were used as a thermal energy storage material in the double passes air solar chimney (SC) collector to get ventilation effect through daytime and after sunset. Air SC collector was installed in the south wall of an insulated test room and tested with different working angles (30o, 45o and 60o). Different SC types were used; single pass, double passes flat plate collector and double pass thermal energy storage box collector (TESB). A computational model based on the finite volume method for transient tw dimensional domains was carried out to describe the heat transfer and storage in the thermal energy storage material of collector. Also, equivalent specific heat method was employed to describe the heat storage and release in the mushy zone. Experimental results referred to an increase in thermal conductivity of paraffin wax that supported by copper foam matrix more than ten times. While the ventilation effect was still active for hours after the sun set, depending on the heat storage amount. Maximum ventilation mass flow rate with TESB collector was recorded with value equals to 36.651 kg/hr., when the overall discharge coefficient that was calculated for the system equals to 0.371. Experimental results showed that the best working angle range was 45~60o, and the highest air to the collector approaching temperature appeared to the double passes flat plate collector. Results gave greater heat storage efficiency of (47)% when the maximum solar radiation was 780 W/m2 at 12.00pm, while the energy summation through duration charge time was 18460 kJ. Computational results, depending on the equivalent heat capacity method for heat storage or release from phase change material that supported by copper foam matrix, showed the behavior of paraffin wax melting and solidification situation through periodic for charge and released heat from the solar collector. Also, these results gave agreement approaching the experimental results for the heat storage in the combined heat storage material, with standard error of 16.8%.

Design of Shell and Tube Heat Exchanger with Double Passes

The exchange of heat is one of the most important processes in the chemical industry. The shell and tube heat exchanger is the major equipment used to transfer heat from one medium to another. This research work on the Computer-Aided Design (CAD) of shell and tube heat exchangers with double passes aims to provide an easy way to design the shell and tube heat exchanger. A case study question was stated and all the necessary calculations in the thermal design were carried out using the Kern’s method of heat exchanger design. The thermal design was then used as a guide to the CAD using computer codes. The computer software program, Visual Basic NET (VB.NET) was used because of its numerous advantages over the other software. The result gotten from the computer-aided design was compared to the result from the thermal design. The computer-aided design software was equally used to test other problems on shell and tube heat exchanger. The computer-aided design was found to be more accurate, quicker and efficient and, it is recommended for use in companies and industries.

Interfacial bonding features of friction stir additive manufactured build for 2195-T8 aluminum-lithium alloy

Friction stir additive manufacturing (FSAM) was performed successfully using 2 mm thick sheets of 2195-T8 aluminum-lithium alloy. The influence of the tool pin shape and process parameters on the interfacial bonding features among the additive manufactured layers was discussed, and the effects of interfacial defects on the performances of the additive build were analyzed based on microstructures, hardness profiles, and mechanical property evaluations. It is shown that the shape of the tool pin is one of the key factors in influencing the bonding interface between two manufactured layers. The cylindrical pin and the conical pin with three flats are not suitable for the FSAM process since very poor material mixing features are produced along the bonding interface. Although the material mixing degree of bonding interface is obviously improved at the advancing side (AS) interface of the nugget zone (NZ) by using the convex featured pin or the pin with three concave arc grooves, the material mixing degree at the retreating side (RS) interface of the NZ is always insufficient. Meanwhile, the weak-bonding defects along the bonding interfaces could be formed, which are originated from the hooking defects on the RS. The weak-bonding defects are related to the oxides and impurities existing at the original bonding interfaces as well as the insufficient stirring action of the tool pin. The back and forth double passes welding is one of the effective methods to improve the material mixing in the whole NZ and eliminate the hooking defects extending into the NZ. The welding rotation speeds of 800, 900 and 1000 rpm for giving welding speed of 100 mm/min were used in the additive manufacturing processes of 2195-T8 aluminum-lithium alloy, in which the optimum microstructure is obtained with the rotation speed of 800 rpm. The soften degree for the multilayered build is obvious, and the hardness profiles across the different bonding interfaces are always uneven. Meanwhile, compared with the AS interface, the fluctuation of the hardness value at the RS interface is greater. The mechanical properties of the multilayered build are inhomogeneous, and the maximum tensile strength of the multilayered build is only reached the 56.6% of the base metal. The mechanical properties are closely associated with the soften tendency of the material and the degree of the amelioration of weak-bonding defect along the bonding interface.

Success Rate of Forensic Surface Search for Osseous Remains in a New England, USA, Environment

Human skeletal remains in outdoor forensic sites often are dispersed from their point of initial deposition, making locating isolated bones difficult. Forested areas in particular may obscure remains, as bones stained from soft-tissue and leaf-litter decomposition may blend in with the forest floor or be hidden by understory. Wide skeletal dispersal presents other problems for searchers, including the difficulty in keeping track of which areas have been searched and maintaining proper spacing of searchers to prevent gapping. Little is known about success rates when searching for dispersed skeletal elements and the effects of searcher spacing, searching the same area twice, type of skeletal element, and understory growth. In order to test recovery rates searching through forested areas, isolated postcranial elements of white-tailed deer ( Odocoileus virginianus ) and crania of pigs ( Sus scrofa ) were laid out randomly in a large grid system and searched for. Overall recovery rates for n = 500 elements were 84.0% on the first pass-through and a cumulative total of 90.0% after the second pass-through, with 10.0% missed after both. Significant differences in recovery rates based upon bone type were noted, but no significant difference was found based upon searcher spacing (1 m vs. 2 m) or understory density (low vs. medium). Forensic archaeologists should note that even with careful searching under controlled conditions, exposed surface skeletal elements can be missed, a concern that is likely amplified under real field search conditions. To maximize remains detection, forensic search protocols should include narrow searcher spacing and double passes through search areas wherever possible.