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The purpose of this paper is to determine: how much the residual curvature could be formed in sintered nano‐silver assembly when it is cooled to room temperature from the sintering temperature (normally 275°C); how the cyclic temperature load affects the residual curvature or stresses in sintered joint. Then the stress level and the reliability of sintered nano‐silver for high‐temperature applications can be understood.

5 mm * 2.5 mm silicon chip was bonded with 96 per cent Al₂O₃ substrate by sintering nanosilver paste. An optical system was developed to measure the curvature of the sintered assemblies. Reliability of the sintered assemblies was evaluated by temperature cycling of −40∼125°C. Finite element analysis was employed to simulate the behavior of the joint subjected to the temperature cycling from −40°C to 125°C by ANSYS. SEM images were taken to investigate the impact of temperature cycling on the reliability of sintered silver attachment.

This residual bending at room temperature was found concave towards the substrate (alumina) side. Also, with the bondline thickness increasing, the residual curvature decreases obviously. The severity of the residual bending in all the structures was mitigated to some extent with increasing number of cycles. There is no crack in the joint with the thickness of 25 μm. The drop of the residual curvature of the samples with bondline of 25 μm is caused mainly by stress relaxation in sintered silver before 300 cycles. Sample with thicker bondline is more susceptible to thermal cycling for the structure bonded with nanosilver than that with thinner bondline. The poor quality of bonding is due to the thicker sintered joint, which means that sintered nanosilver is not suitable for die‐attachment requiring thick bondline.

The paper describes: how a precise optical system was developed to measure the residual curvature of the sintered assemblies; how the evolution of the residual curvature of the sintered assembly with the temperature cycling was obtained by both experiment and simulation; and how microstructures of the sintered silver joint were analyzed for as‐sintered assembly and the sintered assembly after temperature cycling.

The impact of laser peening on curved geometries is not fully comprehended. The purpose of this paper is to explain the action of laser peening on curved components (concave and convex shapes for cylindrical and spherical geometries) by means of shock wave mechanics.

An analytical formulation is derived based on the plasticity incurred inside the material and the results are compared with the prediction by numerical simulation.

A near-linear relationship is observed between curvature and compressive residual stress; an increasing trend was observed for concave models and a decreasing trend was observed for convex models. The consistency in the analytical formulation with the simulation model indicates the behavior of laser peening for curved geometries.

The differences observed in the residual stresses for spherical and cylindrical geometries are primarily due to the effect of Rayleigh waves. This paper illustrates the importance of understanding the physics behind laser peening of curved geometries.

This paper seeks to connect changes in the structure of wages at the occupation level to measures of the task content of jobs. We first present a simple model where skills are used to produce tasks, and changes in task prices are the underlying source of change in occupational wages. Using Current Population Survey (CPS) wage data and task measures from the O*NET, we document large changes in both the within and between dimensions of occupational wages over time, and find that these changes are well explained by changes in task prices likely induced by technological change and offshoring.

The purpose of this paper is to improve the manufacturing of a prosthetic acetabular shell by analyzing the main factors leading to failure during the selective laser melting (SLM) additive manufacturing (AM) process.

Different computer-aided design and computer-aided manufacturing processes have been applied to fabricate acetabular parts. Then, various investigations into surface quality, mechanical properties and microstructure have been carried out to scrutinize the possible limitations in fabrication.

Geometrical measurements showed 1.59 and 0.27 per cent differences between the designed and manufactured prototypes for inside and outside diameter, respectively. However, resulting studies showed that unstable surfaces, cracks, an interruption in powder delivery and low surface quality were the main problems that occurred during this process. These results indicate that SLM is an accurate and promising method for production of intricate shapes, provided that the appropriate settings of production conditions are considered to minimize possible limitations.

The contributions of this paper are discussions covering different issues in the AM fabrication of acetabular shells to improve the mechanical properties, quality and durability of the produced parts.

The current methods for inspecting tall or deep structures such as towers, chimneys, silos, and wells suffer from certain constraints. Manual and assisted inspection methods including humans, drones, wall climbing robots, and others are either costly, have a limited operation time, or affected by field conditions, such as temperature and radiation. This study aims to overcome the presented challenges through a teleoperated soft continuum manipulator capable of inspecting tall or deep structures with high resolution, an unlimited operation time and the ability to use different arms of the manipulator for different environments and structure sizes.

The teleoperated manipulator uses one rotary and two tendon actuators to reach and inspect the interior of a tall (or deep) structure. A sliding part along the manipulator’s body (arm constrainer and tendon router) induces a variable-length bending segment, allowing an inspection camera to be placed at different distances from the desired location.

The experiments confirmed the manipulator’s ability to inspect different locations in the structure’s interior. The manipulator also demonstrated a submillimeter motion resolution vertically and a 2.5 mm per step horizontally. The inspection time of the full structure was 48.53 min in the step-by-step mode and was calculated to be 4.23 min in the continuous mode.

The presented manipulator offers several design novelties: the arm’s thin-wide cross-section, the variable-length bending segment in a fixed-length body, the external rolling tendon routing and the ability to easily replace the arm with another of different material or dimensions to suite different structures and environments.

A study was performed which investigated the wettability of 63Sn‐37Pb and 96.5Sn‐3.5Ag solders on copper and gold ‐nickel plated Kovar ™ using a rosin ‐based, mildly activated (RMA) flux, a water soluble organic acid flux (WS ),and a low residue (LR) flux. The quantitative metric was the contact angle, θ_c, measured by the meniscometer /wetting balance technique. The first part of the study (Part 1) examined wetting performance following continuous exposure to 25°C prior to testing. Then, a preheating step was introduced into the experimental procedure after flux application, but preceding the actual wettability test in order to simulate a factory reflow process; these results are presented in Part II of this study. Contact angles for the 63Sn‐37Pb solder (215°C) on copper were 22±2° with the RMA flux, 12±5° for the WS flux, and 31±6° for the LR flux. Increasing the 63Sn‐37Pb solder temperature to 245°C improved wettability with the RMA and LR fluxes, but no change was observed with the WS fulx. Theii 96.5Sn‐3.5Ag lead ‐free solder exhibited poorer wettability on copper compared with the 63Sn‐37Pb alloy, with contact angles of 41±2° (RMA), 63±15°(WS) and 39±4°(LR). For the gold ‐nickel plated Kovar™ substrates, the 63Sn‐37Pb solder at 215° had contact angles of 15±3°, 35±6° and 29±6° for the RMA, WS and LR fluxes, respectively. The values were reduced at the higher test temperature (245°). The 96.5Sn‐3.5Ag solder also exhibited good wetting performance on the gold ‐nickel plated Kovar™ specimens compared with copper. Analysis of the interfacial tension parameters, γ_SF‐γ_SLand γ_LF ,exemplified the importance of γ_LF as well as the condition of the surfaces (γ_SF ) on wettability performance. A so ‐called ‘combined analysis’ of the 63Sn‐37Pb and 96.5Sn‐3.5Ag wettability data on either copper or gold ‐ nickel plated Kovar™ substrates was used to predict the solder temperature dependence of wettability for the three fluxes and two base materials.

The decision maker is in charge of procurement auctions at the department of transportation of Orangia (a fictitious U.S. state). Students are asked to assist him in estimating the winning bids in various auctions concerning highway repair jobs using data on past auctions. The decision maker is faced with various professional, statistical, and ethical dilemmas.

To analyze highway procurement auctions from the buyer-auctioneer perspective, establish basic facts regarding the project price-to-estimated cost ratio, set up and estimate a structural regression model to predict the winning bid, and compute the probability the winning price will be below estimated cost. Difficulties include heteroskedasticity, logarithmic specification, and omitted variable bias. Also to estimate a Logit regression and predict bidder collusion probability.

Laser powder bed fusion (LPBF) provides the means to produce unique components with almost no restriction on geometry in an extremely short time. However, the high-temperature gradient and high cooling rate produced during the fabrication process result in residual stress, which may prompt part warpage, cracks or even baseplate separation. Accordingly, an appropriate selection of the LPBF processing parameters is essential to ensure the quality of the built part. This study, thus, aims to develop an integrated simulation framework consisting of a single-track heat transfer model and a modified inherent shrinkage method model for predicting the curvature of an Inconel 718 cantilever beam produced using the LPBF process.

The simulation results for the curvature of the cantilever beam are calibrated via a comparison with the experimental observations. It is shown that the calibration factor required to drive the simulation results toward the experimental measurements has the same value for all settings of the laser power and scanning speed. Representative combinations of the laser power and scanning speed are, thus, chosen using the circle packing design method and supplied as inputs to the validated simulation framework to predict the corresponding cantilever beam curvature and density. The simulation results are then used to train artificial neural network models to predict the curvature and solid cooling rate of the cantilever beam for any combination of the laser power and scanning speed within the input design space. The resulting processing maps are screened in accordance with three quality criteria, namely, the part density, the radius of curvature and the solid cooling rate, to determine the optimal processing parameters for the LPBF process.

It is shown that the parameters lying within the optimal region of the processing map reduce the curvature of the cantilever beam by 17.9% and improve the density by as much as 99.97%.

The present study proposes a computational framework, which could find the parameters that not only yield the lowest distortion but also produce fully dense components in the LPBF process.

Supplements the (A) case.