Kenji Amagai

Aluminum foam is expected to be applied in various industrial fields as a lightweight, multifunctional material. When it is used as an industrial product, it is essential to form it into the required shape. There have been some attempts to form aluminum foam. However, the formability remains low. In this study, we attempted to form aluminum foam, which was fabricated by heat foaming a precursor, into a flat plate by reheating it above its foaming temperature and then roller forming it. It was found that heating above the foaming temperature and subsequent roller forming enabled the aluminum foam to be formed into a flat plate without causing defects. In a sample in which the precursor was roller-formed immediately after foaming, it was found that compared to the as-foamed aluminum foam, the decrease in porosity was limited to approximately 5%, enabling roller forming while minimizing the influences on pore structures. In samples that were roller-formed after reheating, porosities slightly decreased, but most pores were retained. Even when the aluminum foam was roller-formed to the same thickness as the initial precursor before foaming, the porosities exhibited around 65%, limiting the reduction in porosities to approximately 15% compared to the as-foamed aluminum foam.

Aluminum foam is attracting attention as a multifunctional, ultra-lightweight material. To apply this aluminum foam to actual industrial materials, aluminum foam plates are required. In addition, it is expected that a multi-layer aluminum foam composed of dissimilar aluminum alloy foam layers can further enhance its functionality. In this study, we attempted to fabricate a three-layer aluminum foam composed of commercially pure aluminum AA1050 and Al-Mg-Si aluminum alloy AA6061 by heating and foaming a total of three pieces of AA1050 precursor and AA6061 precursor arranged alternately, followed by immediate roller joining. It was found that, by traversing a roller immediately after foaming the AA1050 and AA6061 precursors, the aluminum foam could be joined while forming it into a flat plate. In addition, X-ray CT images of the fabricated samples revealed that material flow induced by roller traversing ruptured the surface skin layer. Numerous pores were observed within the sample, indicating pores were maintained during the roller traversing and no significant differences in porosities were identified between AA1050 aluminum foam and AA6061 aluminum foam. Furthermore, from the four-point bending test and the observation of samples after bending test, although quantitative mechanical properties were not obtained due to the as-joined samples were used for the bending test, pores were observed at the fracture surfaces, confirming that roller joining achieved seamless joining.

Aluminum foam is expected to be a leading candidate for lightweight parts due to its light weight and excellent shock-absorption and sound-absorption properties. In order to use it as a part, it is essential to form it into the desired shape. However, the cell walls that form the pores are composed of thin aluminum. When aluminum foam is formed, the cell walls easily fracture and the pores collapse. This results in the loss of the properties of the aluminum foam. Past studies have shown that press forming aluminum foam immediately after foaming, while it is still in the softened state, prevents cell wall failure and pore deformation. In this study, we attempted to perform a continuous process from the foaming of the precursor to the press forming of aluminum foam for three precursors, for the purpose of the continuous production of aluminum foam with desired shapes. It was shown that it is possible to continuously and sequentially foam the precursors by heating and press forming the foamed samples. In addition, aluminum foam with a similar shape, porosity, and pore structure can be fabricated using the continuous process. Also, it was shown that aluminum foam with complex shapes can also be continuously fabricated by using a complex-shaped die. Furthermore, it was indicated that the use of a die in press forming can shorten the cooling time and reduce the production time.

Fluid dynamics modeling was conducted for the supply unit of a Powered Air-Purifying Respirator (PAPR) consisting of a nonwoven fabric filter and a pump, as well as for the exhaust filter (nonwoven fabric). The supply flow rate Q₁ was modeled as a function of the differential pressure ΔP and the duty value d of the PWM control under a constant pump voltage of V = 12.0 [V]. In contrast, the exhaust flow rate Q₂ was modeled solely as a function of ΔP. To simulate the pressurized hood compartment of the PAPR, a pressure buffer and a connected “respiratory airflow simulator” (a piston–cylinder mechanism) were developed. The supply unit and exhaust filter were connected to this pressure buffer, and simulated respiratory flow was introduced as an external disturbance flow. Under these conditions, it was demonstrated that the respiratory state—i.e., the expiratory state (flow from the simulator to the pressure buffer) and the inspiratory state (flow from the pressure buffer to the simulator)—can be estimated from the differential pressure ΔP, the pump voltage V, and the PWM duty value d, with respect to the disturbance flow generated by the respiratory airflow simulator. It was also confirmed that such respiratory state estimation remains valid even when the duty value d of the pump is being actively modulated to control the internal pressure of the PAPR hood. Furthermore, based on the estimated respiratory states, a theoretical investigation was conducted on constant pressure control inside the PAPR and on the inverse pressure control aimed at supporting respiratory activity—namely, pressure control that assists breathing by depressurizing when expiratory motion is detected and pressurizing when inspiratory motion is detected. This study was conducted as part of a research and development project on public-oriented PAPR systems, which are being explored as alternatives to lockdown measures in response to airborne infectious diseases such as COVID-19. The present work specifically focused on improving the wearing comfort of the PAPR.

Aluminum foam is a lightweight material and has excellent shock-absorbing properties. Various properties of aluminum foam can be obtained by changing the base aluminum alloy. Multi-layer aluminum foam can be fabricated by varying the alloy type of the base aluminum alloy, but with different foaming temperatures, within a single aluminum foam to achieve multiple properties. In this study, we attempted to fabricate a two-layer aluminum foam with the upper layer of a commercially pure aluminum A1050 foam and the lower layer of an Al-Si-Cu aluminum alloy ADC12 foam by using an optical heating device that can heat from both the upper and lower sides. Two types of heating methods were investigated. One is to directly stack the A1050 precursor coated with black toner on top of the ADC12 precursor and to foam it from the top and bottom by optical heating. The other is to place a wire mesh between the ADC12 precursor and the A1050 precursor and place the A1050 precursor on the wire mesh, thereby creating a space between the precursors, which is then foamed by optical heating from the top and bottom. It was shown that both precursors can be foamed and joined, and a two-layer A1050/ADC12 foam can be fabricated for both types of heating methods. In the method in which two precursors were stacked and foamed, even if the light intensity of the halogen lamps on the top and bottom were adjusted, heat conduction occurred between the stacked precursors, and the foaming of each precursor could not be controlled, resulting in tilting of the joining interface. In the method of foaming using a wire mesh with a gap between two precursors, it was found that by adjusting the light intensity, the two precursors can be foamed almost simultaneously and achieve similar pore structures. The joining interface can also be maintained horizontally.

In this paper, we investigated the behaviors of bubbles entrained in a film coating during spray coating. Air bubbles that remain in a film coating after diluent evaporation cause coating defects called bubbling defects, including fish-eye and crater defects. In this study, the visualization of a film coating revealed that smaller bubbles in the film shrank slowly and disappeared, while larger bubbles remained. These remaining bubbles grew during the heating process for the drying of the film coating. The shrinking phenomenon was explained using bubble dynamics based on the Young–Laplace equation of a bubble’s inner pressure and Henry’s law for bubble gas dissolution into the film coating. This shrinking model is often used in studies on microbubble dynamics. The results suggested the importance of avoiding the entrainment of large bubbles during the spraying process and enhancing the release of air bubbles from the film coating’s surface through the appropriate usage of defoaming agents.

Owing to its lightweight and excellent shock-absorbing properties, aluminum foam is used in automotive parts and construction materials. If a nondestructive quality assurance method can be established, the application of aluminum foam will be further expanded. In this study, we attempted to estimate the plateau stress of aluminum foam via machine learning (deep learning) using X-ray computed tomography (CT) images of aluminum foam. The plateau stresses estimated by machine learning and those actually obtained using the compression test were almost identical. Consequently, it was shown that plateau stress can be estimated by training using the two-dimensional cross-sectional images obtained nondestructively via X-ray CT imaging.

This paper describes the development of low-speed electric community buses (LSECBs) designed by the author's group and their spread situation in Japan. LSECBs are electric vehicles that can travel on public roads at speeds of less than 5.56 m/s (20 km/h). The university, local government, local businesses, and residents with a co-design approach developed the LSECBs. They have various advantages such as safety due to low speed and low energy consumption. In particular, the LSECBs have features not found in ordinary vehicles, such as the ability to friendly talk with other passengers in the vehicle and to see the surroundings. The purpose of using LSECBs is mostly for sightseeing, but they are also used to enhance the mobility of elderly people in the community. In Japan, public transportation plans are formulated by each local government, but local governments with weak finances do not provide sufficient financial support to the companies responsible for public transportation. As a result, public transportation services have been reduced or eliminated due to the business conditions of private companies, and many elderly people with reduced mobility, called "people with shopping difficulties," have been left behind. Under these situations, it is necessary to discuss what kind of contribution LSECBs can make. Moreover, the LSECBs require special driving methods so as not to cause traffic congestion when mixed with other ordinal vehicles. In this paper, we report on the development concept, features of the LSECBs, their special driving method, positioning as a transportation policy, and their potential as stainable mobility.

In this study, porous ADC12 (Al-Si-Cu alloy) and an A1050 (commercially pure aluminum) dense plate were joined by press working during foaming. The A1050 dense plate was first heated using an optical heating device, and then the ADC12 precursor was placed on the A1050 dense plate. Next, we attempted to join porous ADC12, and the A1050 dense plate by press working during the foaming of porous ADC12. It was shown that porous ADC12 and the A1050 dense plate can be joined by press working during foaming while maintaining the pore shape of porous ADC12. The joined samples exhibited joining strengths higher than the tensile strength of the porous ADC12 itself.