Dakai Bian

An automated imaging system for radiation biodosimetry.

We describe here an automated imaging system developed at the Center for High Throughput Minimally Invasive Radiation Biodosimetry. The imaging system is built around a fast, sensitive sCMOS camera and rapid switchable LED light source. It features complete automation of all the steps of the imaging process and contains built‐in feedback loops to ensure proper operation. The imaging system is intended as a back end to the RABiT—a robotic platform for radiation biodosimetry. It is intended to automate image acquisition and analysis for four biodosimetry assays for which we have developed automated protocols: The Cytokinesis Blocked Micronucleus assay, the γ‐H2AX assay, the Dicentric assay (using PNA or FISH probes) and the RABiT‐BAND assay. Microsc. Res. Tech. 78:587–598, 2015.

The Laser Interlaminar Reinforcement of Continuous Glass Fiber Composites

The Laser Inter-Laminar Reinforcement of Continuous Glass Fiber Composites Huade Tan (Corresponding Author) Graduate Research Assistant Email: ht2288@columbia.edu Phone: 646-691-0720 Fax: 212-666-2393 Gen Satoh Email: gs2358@columbia.edu Y. Lawrence Yao Email: yly1@columbia.edu Manufacturing Research Laboratory Department of Mechanical Engineering Columbia University 500 West 120 st Mudd bldg, rm 220 New York, New York, 10027

Experimental and Numerical Investigation of Laser Forming of Closed-Cell Aluminum Foam

Aluminum foams are generally very attractive because of their ability of combining different properties such as strength, light weight, thermal, and acoustic insulation. These materials, however, are typically brittle under mechanical forming, and this severely limits their use. Recent studies have shown that laser forming is an effective way for foam panel forming. In this paper, the laser formability of Al–Si closed-cell foam through experiments and numerical simulations was investigated. The bending angle as a function of the number of passes at different laser power and scan velocity values was investigated for large- and small-pore foams. In the finite element analysis, both effective-property and cellular models were considered for the closed-cell foam. Multiscan laser forming was also carried out and simulated to study the accumulative effect on the final bending angle and stress states. The maximum von Mises stress in the scanning section was on the order of 0.8 MPa, which was lower than the yield strength of the closed-cell foam material. This paper further discussed the reasonableness and applicability of the two models.

Effects of Laser Radiation on the Wetting and Diffusion Characteristics of Kovar Alloy on Borosilicate Glass

The purpose of this study was to investigate the advantages of laser surface melting for improving wetting over the traditional approach. For comparison, kovar alloy was preoxidized in atmosphere at 700 C for 10 min, and then wetted with borosilicate glass powder at 1100 C with different holding time in atmosphere. The proposed approach used a Nd:YAG laser to melt the surface of the kovar alloy sample in atmosphere, then wetted with borosilicate glass powder at 1100 C with the same holding time. The laser melted surface shows a decrease in contact angle (CA) from 47.5 deg to 38 deg after 100 min. Xray photoelectron spectroscopy (XPS) analysis shows that the surface and adjacent depth have higher concentration of FeO for laser treated kovar (Kovar(L)) than that on traditional thermal treated kovar (kovar(P)). This is attributed to the following improved wetting and diffusion process. The adhesive oxide layer formed on kovar (L) may enhance the oxygen diffusion into the substrate and iron diffusion outward to form an outside layer. This is an another way to enhance the wetting and diffusion process when compared to the delaminated oxide scales formed on kovar (P) surface. The diffusion mechanisms were discussed for both approaches. Scanning electron microscope (SEM) revealed that an iron oxide interlayer in the joint existed under both conditions. Fayalite nucleated on the iron oxide layer alloy and grew into the glass. In both cases, neither Co nor Ni were involved in the chemical bonding during wetting process. The work has shown that laser surface melting can be used to alter the wetting and diffusion characteristics of kovar alloy onto borosilicate glass. [DOI: 10.1115/1.4037426]

Liquid Handling Optimization in High-Throughput Biodosimetry Tool

Due to the need of high-speed and efficient biodosimetric assays for triage and therapy in the event of radiological or nuclear attack, a robotically based automated biodosimetry tool (RABiT) has been developed over the past few years. Adapting the micronucleus assay from filter plates to V-shaped plates presented challenges in the liquid handling, namely, cell splashing out of the V-shaped well plate during the cell harvesting, poor cell distribution on the bottom of the image plate during the dispensing, and cell loss from the image plate during the aspiration in the liquid handling process. Experimental and numerical investigations were carried out to better understand the phenomena and mitigate the problems. Surface tension and contact angle among the fluids and the plate wall were accounted for in the discrete and multiphase numerical models. Experimental conditions were optimized based on the numerical results showing the relationship between nozzle speed and amount of splashed liquid, and the relationship between aspiration speed and number of escaped cells. Using these optimized parameters, numbers of micronuclei in binucleated cells showed the same dose dependence in the RABiT-prepared samples as those in the manually prepared ones. Micronucleus assay protocol was fully realized on RABiT.

Interlaminar Toughening of GFRP—Part II: Characterization and Numerical Simulation of Curing Kinetics

Various methods of toughening the bonding between the interleaf and laminate glass fiber reinforced polymer (GFRP) have been developed due to the increasing applications in industries. A polystyrene (PS) additive modified epoxy is used to improve the diffusion and precipitation region between polysulfone (PSU) interleaf and epoxy due to its influence on the curing kinetics without changing glass transition temperature and viscosity of the curing epoxy. The temperature-dependent diffusivities of epoxy, amine hardener, and PSU are determined by using attenuated total reflection–Fourier transfer infrared spectroscopy (ATR–FTIR) through monitoring the changing absorbance of their characteristic peaks. Effects of PS additive on diffusivity in the epoxy system are investigated by comparing the diffusivity between nonmodified and PS modified epoxy. The consumption rate of the epoxide group in the curing epoxy reveals the curing reaction rate, and the influence of PS additive on the curing kinetics is also studied by determining the degree of curing with time. A diffusivity model coupled with curing kinetics is applied to simulate the diffusion and precipitation process between PSU and curing epoxy. The effect of geometry factor is considered to simulate the diffusion and precipitation process with and without the existence of fibers. The simulation results show the diffusion and precipitation depths which match those observed in the experiments. [DOI: 10.1115/1.4036127]

Interlaminar Toughening of GFRP—Part I: Bonding Improvement Through Diffusion and Precipitation

A low concentrated polystyrene (PS) additive to epoxy is used, since it is able to reduce the curing reaction rate but not at the cost of increasing viscosity and decreasing glass transition temperature of the curing epoxy. The modified epoxy is cocured with a compatible thermoplastic interleaf during the vacuum assisted resin transfer molding (VARTM) to toughen the interlaminar of the composites. Using viscometry, the solubilities of thermoplastics (TPs) polycarbonate (PC), polyetherimide (PEI), and polysulfone (PSU) are determined to predict their compatibility with epoxy. The diffusion and precipitation process between the most compatible polymer PSU and epoxy formed semi-interpenetration networks (semi-IPN). To optimize bonding adhesion, these diffusion and precipitation regions were studied via optical microscopy under curing temperatures from 25 C to 120 C and PS additive concentrations to epoxy of 0–5%. Uniaxial tensile tests were performed to quantify the effects of diffusion and precipitation regions on composite delamination resistance and toughness. Crack paths were observed to characterize crack propagation and arrest mechanism. Fracture surfaces were examined by scanning electron microscopy (SEM) to characterize the toughening mechanism of the thermoplastic interleaf reinforcements. The chemically etched interface between diffusion and precipitation regions showed semi-IPN morphology at different curing temperatures. Results revealed deeper diffusion and precipitation regions increase energy required to break semi-IPN for crack propagation resulting in crack arrests and improved toughness. [DOI: 10.1115/1.4036126]

Effect of Deep Penetration of Interleaf on Delamination Resistance in GFRP

The problem of improving the delamination resistance and toughness of laminate fiber-reinforced composites especially for the drop-off structure is receiving considerable attention with the increasing need and application in industries. A hot melt-bonding process is developed to bond glass fabric laminates and the thermoplastic (TP) polysulfone (PSU) interleaf prior to the vacuum assisted resin transfer molding (VARTM) of laminate composites. The TP interleaf is heated above the glass transition temperature to reduce the viscosity when penetrating deeply into the glass fiber fabric. Mechanical tensile testing is performed to quantify the effects of the penetration depth on composite delamination resistance and composite toughness under different melt-bonding temperatures. Crack paths are observed by optical microscopy to characterize the crack propagation and arrest mechanism. Postmortem high-resolution imaging of the fracture surfaces is used to characterize the toughening mechanism of the TP interleaf reinforcements by using scanning electron microscopy (SEM). With deep penetration of the interleaf into the fiber bundles, cracks arrested within the penetration region improve the toughness by avoiding the cracks to reach the weak interface between interleaf and epoxy.

Effects of laser radiation on the wetting and diffusion characteristics of kovar alloy on borosilicate glass

The purpose of this study was to investigate the advantages of laser surface melting for improving wetting over the traditional approach. For comparison, kovar alloy was preoxidized in atmosphere at 700℃ for 10min, and then wetted it with borosilicate glass powder at 1100℃ with different holding time in atmosphere. The proposed approach used a Nd:YAG laser to melt the surface of the kovar alloy sample in atmosphere, then wetted with borosilicate glass powder at 1100℃ with the same holding time. The laser melted surface shows a decrease in contact angle from 47.5 degrees to 38 degrees after 100 minutes. The diffusion mechanisms were discussed for both approaches. Scanning electron microscope revealed that an iron oxide interlayer in the joint existed under both conditions. Fayalite nucleated on the iron oxide layer alloy and grew into the glass. In both cases, neither Co nor Ni were involved in the chemical bonding during wetting process. The work has shown that laser surface melting can be used to alter the wetting and diffusion characteristics of kovar alloy to borosilicate glass. This work demonstrates that it is possible to alter the wetting characteristics of Kovar alloy using the laser to melted kovar surface in atmosphere to substitute forthe traditionsal thermal treatment of kovar.The purpose of this study was to investigate the advantages of laser surface melting for improving wetting over the traditional approach. For comparison, kovar alloy was preoxidized in atmosphere at 700℃ for 10min, and then wetted it with borosilicate glass powder at 1100℃ with different holding time in atmosphere. The proposed approach used a Nd:YAG laser to melt the surface of the kovar alloy sample in atmosphere, then wetted with borosilicate glass powder at 1100℃ with the same holding time. The laser melted surface shows a decrease in contact angle from 47.5 degrees to 38 degrees after 100 minutes. The diffusion mechanisms were discussed for both approaches. Scanning electron microscope revealed that an iron oxide interlayer in the joint existed under both conditions. Fayalite nucleated on the iron oxide layer alloy and grew into the glass. In both cases, neither Co nor Ni were involved in the chemical bonding during wetting process. The work has shown that laser surface melting can be used to alter t...

Experimental and numerical investigation of laser forming of closed-cell aluminum foam

Aluminum foams are generally attractive because of their ability of combining different properties such as strength, light weight, thermal and acoustic insulation. These materials, however, are typically brittle under mechanical loading and this severely limits their use. Recent studies have shown that laser forming is an effective way to shape foam panels . In this paper, the laser forming of Al-Si closed-cell foam was investigated through experiments and numerical simulations.Bending angle as a function of the number of passes at different laser power and scan velocity values was obtained for large- and small-pore foams. In the finite element analysis, both effective-property and cellular models were considered for the closed-cell foam. Multi-scan laser forming was also simulated to study the accumulative effect on the final bending angle. Results confirmed that temperature gradient mechanism (TGM) was dominant during laser forming of the closed-cell Al-Si foam material under the conditions considered. This paper further discussed the reasonableness and applicability of the two models. The effective-property model predictions generally agree with experimental results of multi-scan laser forming. The cellular model somewhat underestimates the temperature gradients in the thickness direction but significantly overestimates the stress level likely due to the fact that the non-homogeneity in pore shape, size and distribution was inadequately accounted for.Aluminum foams are generally attractive because of their ability of combining different properties such as strength, light weight, thermal and acoustic insulation. These materials, however, are typically brittle under mechanical loading and this severely limits their use. Recent studies have shown that laser forming is an effective way to shape foam panels . In this paper, the laser forming of Al-Si closed-cell foam was investigated through experiments and numerical simulations.Bending angle as a function of the number of passes at different laser power and scan velocity values was obtained for large- and small-pore foams. In the finite element analysis, both effective-property and cellular models were considered for the closed-cell foam. Multi-scan laser forming was also simulated to study the accumulative effect on the final bending angle. Results confirmed that temperature gradient mechanism (TGM) was dominant during laser forming of the closed-cell Al-Si foam material under the conditions considered. ...