Porous metals and metallic foams are presently the focus of very active research and development activities. There are currently around 150 institutions working on metallic foams worldwide, most of them focussing on their manufacture and characterisation. Various companies are developing and producing these materials which are now being used in numerous industrial applications such as lightweight structures, biomedical implants, filters, electrodes, catalysts, and heat exchangers. This review summarizes recent developments on these materials, with particular emphasis on research presented at the latest International Conference on Porous Metals and Metallic Foams (MetFoam 2007).

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Porous Metals and Metallic Foams: Current Status and Recent Developments†

Friction stir welding (FSW) is a widely used solid state joining process for soft materials such as aluminium alloys because it avoids many of the common problems of fusion welding. Commercial feasibility of the FSW process for harder alloys such as steels and titanium alloys awaits the development of cost effective and durable tools which lead to structurally sound welds consistently. Material selection and design profoundly affect the performance of tools, weld quality and cost. Here we review and critically examine several important aspects of FSW tools such as tool material selection, geometry and load bearing ability, mechanisms of tool degradation and process economics.

Review: friction stir welding tools

Friction stir welding: Process, automation, and control

Soft dielectric materials typically exhibit poor heat transfer properties due to the dynamics of phonon transport, which constrain thermal conductivity (k) to decrease monotonically with decreasing elastic modulus (E). This thermal-mechanical trade-off is limiting for wearable computing, soft robotics, and other emerging applications that require materials with both high thermal conductivity and low mechanical stiffness. Here, we overcome this constraint with an electrically insulating composite that exhibits an unprecedented combination of metal-like thermal conductivity, an elastic compliance similar to soft biological tissue (Young's modulus 600% strain). By incorporating liquid metal (LM) microdroplets into a soft elastomer, we achieve a ∼25× increase in thermal conductivity (4.7 ± 0.2 W⋅m-1⋅K-1) over the base polymer (0.20 ± 0.01 W⋅m-1·K-1) under stress-free conditions and a ∼50× increase (9.8 ± 0.8 W⋅m-1·K-1) when strained. This exceptional combination of thermal and mechanical properties is enabled by a unique thermal-mechanical coupling that exploits the deformability of the LM inclusions to create thermally conductive pathways in situ. Moreover, these materials offer possibilities for passive heat exchange in stretchable electronics and bioinspired robotics, which we demonstrate through the rapid heat dissipation of an elastomer-mounted extreme high-power LED lamp and a swimming soft robot.

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High thermal conductivity in soft elastomers with elongated liquid metal inclusions

Spot welding, particularly resistance spot welding (RSW), is a critical joining process in automotive industry. The development of advanced high strength steels for applications in automotive industry is accompanied with a challenge to better understand the physical and mechanical metallurgy of these materials during RSW. The present paper critically reviews the fundamental understanding of structure–properties relationship in automotive steels resistance spot welds. The focus is on the metallurgical characteristics, hardness–microstructure correlation, interfacial to pullout failure mode transition and mechanical performance of steel resistance spot welds under quasi-static, fatigue and impact loading conditions. A brief review of friction stir spot welding, as an alternative to RSW, is also included.

Critical review of automotive steels spot welding: process, structure and properties

http://www.lib.kobe-u.ac.jp/repository/90002185.pdf

Analysis of effect of tool geometry on plastic flow during friction stir spot welding using particle method

Design and heat transfer characteristics of new plate heat exchanger.

Natural convection to air from an array of vertical parallel plates with discrete and protruding heat sources

An estimation method of the plane directional thermal conductivity of fibrous insulations using the cyclic heat method and the transient hot-wire method is proposed. By assuming that the thermal conductivity λ

 h
 of anisotropic materials measured by the transient hot-wire method is equivalent to that of the isotropic materials which have the same bulk density ρ and specific heat c as the anisotropic materials, the thermal conductivity λ

 h
 is shown to be equal to 
$$\sqrt {\lambda _x \lambda _y } $$

 , which is a geometrical mean of the thermal conductivities in the direction of the plane λ

 x
 and the thickness λ

 y
 of the anisotropic materials. For an alumina silica blanket (ρ=125 kg·m−3), the thermal conductivities λ

 h
 , λ

 x
 , and λ

 y
 were measured in the temperature range between −140 and 300°C using the transient hot-wire method for λ

 h
 and the cyclic heat method for λ

 x
 and λ

 y
 . In the same way, the thermal conductivities λ

 h
 , λ

 x
 , and λ

 y
 of a rock wool (ρ=121 kg·m−3) insulation were also measured in the temperature range, 100 to 600°C. From a comparison of the measured results with the estimated values of λ

 x
 , it is confirmed that the proposed method can estimate the measured values reasonably well.

Toshio Tomimura

Papers

Analysis of effect of tool geometry on plastic flow during friction stir spot welding using particle method

Design and heat transfer characteristics of new plate heat exchanger.

Natural convection to air from an array of vertical parallel plates with discrete and protruding heat sources

Estimation of the Mean Thermal Conductivity of Anisotropic Materials

Experimental study on multi-layered type of gas-to-gas heat exchanger using porous media