Radiative-thermal models of light transport in tissue are presented that stimulates the thermal effects of pulsed laser radiation on very thin scattering and absorbing biological layers. Thermal therapies require a firm understanding of temperature-depth relationship for tissue modification or destruction, especially through very thin layers that are characterized by contrasting opto-thermal properties. Temperature distribution in biological layers of thicknesses in the order of their mean free path or less are evaluated before the onset of thermal diffusion for both the traditional model of Monte Carlo simulation and that with new features tailored for very thin layers. Temperature dynamics in very thin layers such as skin in dermatology is a typical example. For instance, during the heating of small volumes of tissue as in fractional photothermolysis, nonablative dermal remodeling and ablative skin resurfacing, short pulse lasers are used by choosing pulse length sufficiently short that will not damage the surrounding healthy tissue, but sufficiently long enough to allow damage, necrosis or coagulation over the entire target area. This is in contrast to the situation where thermal dissipation due to heat conduction is the principal determinant of tissue damage. Numerical results obtained from both models differ significantly. While the model designed specifically for very thin scattering layers tends to confine temperature rise to specific layers, the traditional model have a tendency to misjudge the layers of interest thereby giving rise to temperature increase in undesired locations. These results will advance our understanding of radiation transport in layers that are extremely very thin, and help develop better treatment modules for laser therapeutic treatment regimes in surgery and dermatology.

Endovascular treatment has become the standard for intracranial aneurysm management. In vitro systems including an artery model are required for devices evaluation and clinician training. Although silicone is usually use for such model, its compliance is known to be lower than blood vessels. The purpose of this study was to analyze the influence of model material compliance on flow properties. Silicone and 12 [wt%] poly (vinyl alcohol) hydrogel (PVA-H) were used to create two box-shaped models of significantly different compliance. The inner lumen geometry was a 4 [mm] diameter straight tube (parent vessel) and a 10 [mm] diameter sphere representing the aneurysm. A blood-mimicking fluid made of a mixture of glycerin, water and sodium iodide was used to reproduce the viscosity and density of blood and fit models refractive index. The circulation system consisted of a pulsatile blood pump and resistance valve. A flow rate of 250±50 [ml/min] and pressure from 75 to 115 [mmHg] were set inside the model. Pressure and flow rate sensors were used to monitor flow conditions before and after the model. Particle image velocimetry (PIV) was performed to record the difference of flow patterns inside the aneurysm of both model using a Nd:YAG solid laser system and fluorescent particles. Results revealed a significant change of flow conditions due to model compliance. Attenuation of the flow rate pulse was recorded between the inlet and the outlet of the both model. This attenuation was 51% for PVA-H model. Moreover, a time lag between outlet pressure and outlet flow rate curves was recorded in both model. This time lag was longer with the PVA-H model, as this model exhibit a greater compliance. PIV experiments revealed significant changes of flow patterns and velocity inside the aneurysm. Because of its high compliance, PVA-H model walls moved under the pulsatile conditions. A change of flow direction and decrease of its velocity were observed near the proximal wall of the aneurysm, compared to the silicone model. Such differences might modify the stress on the wall of the aneurysm. To conclude, our experiments revealed that compliance has significant impacts on flow properties and should be taken into account for in vitro vascular model manufacturing.

Cold-flow spray researchers have an array of diagnostic tools to extract meaningful information on spray characteristics. The efficacy of many of these tools, however, depends heavily on calibration, alignment, and human operation. This can lead to large discrepancies in data values for seemingly identical setups between workers. The application of experimental data to numerical models is thereby hindered due to inconsistencies in results caused by experimental error. Previously, an attempt was made to produce a “standard spray” through the use of a research simplex atomizer (RSA). As manufacturing processes and diagnostic tools have improved, the research simplex atomizer is being revisited. Here, a new research simplex atomizer has been investigated. Fundamental datasets captured from detailed test conditions are presented to provide benchmark data with the intention of other workers testing the reproducibility of the results. Preliminary findings between laboratories show good agreement in droplet size measurements. Further, emphasis is placed on the sensitivity of laser diagnostics used and the effect their operation can incur. To satisfy the requirements of a measurement standard, it is paramount that all workers adhere to similar diagnostic configurations and detail their operating parameters.

A continuously scanning laser Doppler vibrometer (CSLDV) system is capable of efficient and spatially dense vibration measurements by sweeping its laser spot along a scan path assigned on a structure. This paper proposes a new operational modal analysis (OMA) method based on a data processing method for CSLDV measurements of a structure, called the lifting method, under white-noise excitation and applies a baseline-free method to identify structural damage using estimated mode shapes from the OMA method. The lifting method enables transformation of raw CSLDV measurements into measurements at individual virtual measurement points, as if the latter were made by use of an ordinary scanning laser Doppler vibrometer in a step-wise manner. It is shown that a correlation function with non-negative time delays between lifted CSLDV measurements of two virtual measurement points on a structure under white-noise excitation and its power spectrum contain modal parameters of the structure, i.e., natural frequencies, modal damping ratios and mode shapes. The modal parameters can be estimated by using a standard OMA algorithm. A major advantage of the proposed OMA method is that curvature mode shapes associated with mode shapes estimated by the method can reflect local anomaly caused by small-sized structural damage, while those estimated by other existing OMA methods that use CSLDV measurements cannot. Numerical and experimental investigations are conducted to study the OMA method and baseline-free structural damage identification method. In the experimental investigation, effects of the scan frequency of a CSLDV system on the two methods were studied. It is shown in both the numerical and experimental investigations that modal parameters can be accurately estimated by the OMA method and structural damage can be successfully identified in neighborhoods with consistently high values of curvature damage indices.

A multiscale modeling that integrates electronic scale ab initio quantum mechanical calculation, atomic scale molecular dynamics simulation, and continuum scale two-temperature model description of the femtosecond laser processing of nickel film at different thicknesses is carried out in this paper. The electron thermophysical parameters (heat capacity, thermal conductivity, and electron-phonon coupling factor) are calculated from first principles modeling, which are further substituted into molecular dynamics and two-temperature model coupled energy equations of electrons and phonons. The melting thresholds for nickel films of different thicknesses are determined from multiscale simulation. Excellent agreement between results from simulation and experiment is achieved, which demonstrates the validity of modeled multiscale framework and its promising potential to predict more complicate cases of femtosecond laser material processing. When it comes to process nickel film via femtosecond laser, the quantitatively calculated maximum thermal diffusion length provides helpful information on choosing the film thickness.

Damage precursor in composites can lead to large structural damages, such as delamination, in carbon fiber reinforced plastic (CFRP) composites due to complex load conditions and environmental effects. In addition, multiple types of damage precursors including micro-scale matrix cracks, fiber pull-out from matrix, and fiber breakages, are extremely difficult to detect due to the limitation of resolution of current non-destructive evaluation (NDE) technologies. This paper presents a photo-acoustic based non-contact NDE system for the detection of damage precursors with extremely high resolution up to one hundred micrometers. This system consists of three major components: picoseconds pulsed laser based ultrasonic actuator, ultrasound receiver, and data processing and computing subsystem. Picoseconds pulsed laser is used to generate ultrasonic propagations in composites during the NDE process, and the ultrasound signals are recorded by the ultrasound receiver. Three-dimensional microstructure of the individual composites grid within the composite is able to be reconstructed for further analysis. The size and position of the damage precursors are evaluated with high accuracy up to 100 μm. The experimental results demonstrate that this imaging system is able to provide a novel non-contact approach with extremely high resolution for damage detection of CFRP composites. In addition, the developed NDE system has a wide industrial application in aerospace, automobile, civil, mechanical, and other key industries.

Selective Laser Melting (SLM) and Electron Beam Additive Manufacturing (EBAM) are two of the most promising additive manufacturing technologies that can make full density metallic components using layer-by-layer fabrication methods. In this study, three-dimensional computational fluid dynamics models with Ti-6Al-4V powder were developed to conduct numerical simulations of both the SLM and EBAM processes. A moving conical volumetric heat source with Gaussian distribution and temperature-dependent thermal properties were incorporated in the thermal modeling of both processes. The melt-pool geometry and its thermal behavior were investigated numerically and results for temperature profile, cooling rate, variation in specific heat, density, thermal conductivity, and enthalpy were obtained with similar heat source specifications. Results obtained from the two models at the same maximum temperature of the melt pool were then compared to describe their deterministic features to be considered for industrial applications. Validation of the modeling was performed by comparing the EBAM simulation results with the EBAM experimental results for melt pool geometry.

In the Suspended ThermoReflectance (STR) technique a microcantilever is heated with a laser power at the free end of the microcantilever and as heat propagates through it, another laser is used to measure the temperature along the beam.[1] In this paper, the heat equation is solved for two-dimensional heat flow in the microcantilever to determine the material’s thermal conductivity and heat capacity. Two of the dimensions of the microcantilever, width and length, are significantly greater than the third dimension, the thickness, leading to the two-dimensional approximation. Two boundaries along the length of the structure and one boundary along the width are assumed to be under Dirichlet boundary conditions, while the other boundary has Neumann condition. The Neumann or flux condition has a Gaussian profile due to the nature of laser beam intensity. The heat equation is solved using under 3 different flux conditions: (1) Steady-state, (2) Transient, and (3) Periodic. A steady-state condition mimics the experimental condition when a continuous wave laser is used to heat the microcantilever’s tip. A transient condition is possible when quickly removing or adding the continuous wave laser’s flux from the microcantilever’s tip using a chopper. Finally, a periodic condition can be achieved when an electro-optic modulator is utilized experimentally. Closed form analytical expressions are evaluated against the finite element model and experimental results for microcantilever beams and micro-structures of Si that have lengths on the order of a mm, width on the order of 100 microns, and thicknesses of 1 micron or less.

In the present work, the deformation behavior in metallic film subjected to ultra-short laser heating is investigated. Static thermo-elastic behavior is predicted for 100 nm thin film of either single layer or multiple layers. The temperature distribution is estimated from dual-phase lag non-Fourier heat conduction model. The maximum temperature after single pulse is achieved 730 K. The temperature profile for this pulse laser is used to compute elastic stress and distortion field following the minimization of potential energy of the system. In the present work, the simulation has been proposed by developing 3D finite element based coupled thermo-elastic model using dual phase lag effect. The experimental basis of transient temperature distribution in ultra-short pulse laser is extremely difficult or nearly impossible, the model results have been validated with literature reported thermal results. Since the temperature distribution due to pulse laser source varies with time, the stress analysis is performed in incremental mode. Hence, a sequentially coupled thermo-mechanical model is developed that is synchronized between thermal and mechanical analysis in each time steps of transient problem. The maximum equivalent stress is achieved 0.3 GPa. Numerical results show that the predicted thermal stress may exceeds the tensile strength of the material and may lead to crack or damage the thin film.

The temperature evolution of nanoparticle packings on a substrate under high laser power is investigated both experimentally and via numerical simulations. Numerical modeling of temperature distributions in copper nanoparticle packings on a glass substrate is performed and results are compared with experiment under 2.6 kW/cm 2 laser power. A coupled electromagnetic-heat transfer model is implemented to understand the nanoparticle temperature distribution. Very good agreement between the coupled electromagnetic-heat transfer model and the experimental results is obtained by matching the interfacial thermal conductance, G, between the nanoparticles using the experimental result in the coupled electromagnetic-heat transfer model.

Alloy parts fabricated by the selected laser melting (SLM) additive manufacturing process generally contain many defects. Non-destructive Positron Annihilation Lifetime Spectroscopy (PALS) measurements were applied to evaluate these defects. The two-component positron lifetime method was used to analyze the evolution of two types of defects, mono-vacancy and vacancy cluster. Stainless steel 316 SLM samples were prepared using two sets of SLM processing parameters. For SLM samples, the temperature effect of heat treatment was examined by PALS. The effect of plastic deformation is also examined using PALS.

The application of laser processing as a surface treatment method on oxide dispersion strengthened (ODS) Fe-14Cr ferritic alloys, Fe-14Cr-3W-0.3Ti-xY 2 O 3 (x = 0.3, 0.6, 0.9) (wt%), was examined in this paper. The ODS ferritic alloys with different amount of Y 2 O 3 particles were prepared by mechanical milling and subsequently consolidated by spark plasma sintering (SPS). The effect of surface laser processing on the corrosion behavior was investigated for these ODS alloys with different oxide contents. The corrosion behaviors of SPS consolidated ODS samples with subsequent laser melting/solidification were examined by the means of electrochemical tests and compared with the untreated ODS samples in salt water. Results indicated that for samples without laser treatment, powders are mainly in their elemental state. However, after laser processing, the formation of passive layer and the improvement in the corrosion resistance are noticeable. CALculation of PHAse Diagrams (CALPHAD) calculations were used to identify the equilibrium phases and compared well with the experimental results.

In the current study, the influence of different rotation conditions on the flow behavior is experimentally investigated by a new system which is designed for time-resolved PIV measurements of the smooth channels at rotation conditions. The Reynolds number equals 15000 and the rotation number ranges from 0 to 0.392 with an interval of 0.098. This new time-resolved Particle Image Velocimetry system consists of a 10 Watts continuous laser diode and a high-speed camera. The laser diode can provide a less than 1mm thickness sheet light. 6400 frames can be captured in one second by the high-speed camera. These two parts of the system are fixed on a rotating disk. In this case, the relative velocity of flows in the rotating smooth square channel can be measured directly to reduce the measurement error. This system makes high-speed camera close to the rotating channel, which allows a high resolution for the measurements of main stream. In addition, high accuracy and temporal resolution realize a detailed analysis of boundary layer characteristics in rotation conditions. Based on this system, experimental investigation has been undertaken. Results are presented of the evolution of velocity and boundary layer thickness at various rotation numbers and different circumferential positions.

Whispering gallery mode (WGM) resonators exhibit high quality factor Q and a small mode volume; they usually exhibit high resolution when used as sensors. The light trapped inside a polymeric micro-cavity travels through total internal reflection generating the whispering gallery modes (WGMs). A laser or a lamp is used to power the microlaser by using a laser dye embedded within the resonator. The excited fluorescence of the dye couples with the optical modes. The optical modes (laser modes) are seen as sharp peaks in the emission spectrum with the aid of an optical interferometer. The position of these optical modes is sensitive to any change in the morphology of the resonator. However, the laser threshold of these microlasers is of few hundreds of microjoules per square centimeter (fluence) usually. In addition, the excitation wavelength’s light powering the device must be smaller than the microlasers size. When metallic nanoparticles are added to the microlaser, the excited surface plasmon couples with the emission spectrum of the laser dye. Therefore, the fluorescence of the dye can be enhanced by this coupling; this in turn, lowers the power threshold of the microlaser. Also, due to a plasmonic effect, it is possible to use smaller microlasers. In addition, a new sensing modality is enabled based on the variation of the optical modes’ amplitude with the change in the morphology’s microlaser. This opens a new avenue of low power consumption microlasers and photonics multiplexed biosensors.

A method to fabricate high temperature protective structural coating on top of critical gas turbine components by additive manufacturing (AM) technique using oxide dispersion strengthening (ODS) powder is presented. A novel combined mechanochemical bonding (MCB) plus ball milling (BM) process is utilized to produce ODS powders with nano-crystalline gamma prime phase. AM-assisted ODS coating by direct energy deposition (DED) method on MAR-247 substrate, with laser powers from 100W to 200W were carried out. The ODS coated samples were then subjected to cyclic thermal loadings for over 2000 cycles. Depth-profiling x-ray photoelectric spectroscopy (DP-XPS) was applied for detailed oxide formation analyses through the ODS coating layer at various thermal cycles. Corresponding mechanical properties such as Young’s modulus, yield strength and hardening component of ODS coating samples at various thermal cycles were measured at room temperature using an in-house developed non-destructive spherical micro-indentation testing method. Correlation of the measured mechanical properties with evolution of the ODS microstructures are studied. In particular, stability of gamma prime phase in the ODS coating after thermal cycles is analyzed. Test results revealed a thin steady durable alpha alumina oxide layer on ODS coating surface. After 2,200 thermal cycles, strong bonding at ODS/substrate interface is maintained for ODS coated samples with 200W laser power. Test results also showed stable substrate microstructures due to the protective ODS coating even after 2,200 thermal cycles.

The automotive industry corporations noticed the advantages of automated laser welding. Robot laser welding systems have immediately attracted their interests for bringing down the production costs and delivering higher-quality items. The objective of this research is to study how to enhance heat dissipation to endorse a better performance of the pressure wheel, and help achieve a longer life cycle. Transient thermal analysis of the pressure wheel was conducted using ANSYS workbench. The work studied the effects of different design models and materials on the thermal performance of pressure wheel assembly during the cooling period. Numerical simulations were performed on both solid and geometrically ventilated wheels for enhancing the heat dissipation performance of the wheel. Different materials were also be tested and compared. The analysis will support the design process by monitoring different parameters in terms of performance, heat loss and manufacturing cost. A comparison was made for two different designs each with three different materials and the best design was selected. The simulation results in a period of 50 seconds cooling time showed that the temperature dropped with the 1st design (full solid wheel) made of tungsten from an initial temperature T i = 500 K to a final temperature of Tf = 434.5 K. Tungsten was found to have better heat dissipation compared to stainless steel and cast iron. For the 2nd design (geometrically ventilated wheel) made of tungsten, the temperature drops from T i = 500 K to Tf = 422.1 K. Comparing the two designs, the geometrically ventilated wheel was proved to be cooled faster. The present work will help improve the performance of pressure wheel in the welding industry by providing computational results for successive design testing and data validation.

This study aims at analyzing process-induced pores in selective laser melting (SLM), a laser powder-bed fusion additive manufacturing (AM) process. Porosity is one of the most problematic defects in SLM parts; it impairs the part performance, and yet, is sharply sensitive to the parameters of the SLM process itself. Detailed analysis of SLM pore formations using a computed tomography (CT) technique is desired in order to understand the porosity level under different process conditions. In this study, an SLM system was used to fabricate samples, using Ti-6Al-4V powder, with single tracks formed, at 60 μm layer thickness, with different laser powers and scanning speeds to vary the energy density. A micro-CT (μ-CT) scanner was used to measure the internal features of the SLM specimens without any post-build treatments and to analyze the porosity inside single tracks formed with different energy densities. There are different mechanisms of pore formation in SLM, in particular, this study first focuses on the pore formation due to the keyhole phenomenon, caused by a high energy density. μ-CT scanning at a 6 μm resolution is able to clearly reveal the pores in the SLM samples. From the CT scan and analysis results, it is observed that increasing the energy density increases the volume of pores. For example, with 195 W and 200 mm/s, the number of pores is 93 and the total pore volume is 0.014 mm 3 for a scanning length of 12 mm. On the other hand, if the energy density is less than 0.24 J/mm, few or no pores were observed, because possibly the melting process changes from the keyhole mode to the conduction mode.

Selective laser heat treatment allows local modification of material properties and can have wide range of applications within the automotive industry. Enhanced formability and strength are possible to achieve. As the process involves selective heating, positioning of the heat treatment pattern in local areas is vital. Pattern positioning is often suggested based on the part design and forming aspects of the material to avoid failures during manufacturing. Along with improving material properties in desired local areas, the process also produces unwanted distortion in the material. Such effects on variation should be considered and minimized. In this paper, heat treatment pattern is offset from its original position and its effect on geometrical variation is investigated. Boron steel blanks are selectively laser heat treated with a specific heat treatment pattern and then stamped to desired shape. Two heat treatment pattern dimensions are examined. Variation at blank level and after stamping, and springback after stamping is observed. Results show that pattern offsetting leads to higher geometrical variation. Therefore, correct positioning of heat treatment pattern is important to minimize its effect on geometrical variation along with enhancing the material properties. Knowledge from this study will contribute to various stages of the geometrical assurance process.

Conventional machining of complex parts having three-dimensional curved surfaces is performed in two steps using a five-axis machining center and a grinding machine. There is a problem with productivity. Therefore, we developed a CNC lathe to cope with high-speed machining. The newly developed CNC lathe has four axes (X1, X2, Z, C). In this machining, the tool on the X axis follows the curved surface synchronously with the rotation angle of the spindle. This cutting method enables machining of the three-dimensional curved surface. By adopting a linear motor for the X axis, high-speed reciprocal motion of the tool is realized, and the machining time has been reduced to approximately 1/30, as compared with the conventional milling process. In this operation, since high-response motion is required for the tool positioning, a certain profile error remains even if repeated control is applied using the linear scale. In the present study, for the purpose of improving the contour accuracy of a three-dimensional curved surface, we report the result of compensation between the profile measurement method of workpiece and the desired profile accuracy. After machining a three-dimensional curved surface by the developed CNC lathe, a line laser displacement sensor is used to measure the workpiece profile on the machine without removing the workpiece. The position of the machining program is measured by synchronizing the controller of the CNC lathe and the line laser displacement gauge. In addition, the desired profile accuracy is improved by compensating for the error between the desired profile accuracy and the measurement result.

Due to the advantages of high efficiency, good flexibility and large measurement scale, the laser tracker measurement method is widely used in the error measurement of the machine tool. For the laser tracker measurement, the selection of the measuring points in the workspace has a significant influence on the identification effect of the errors. In this paper, the method to select the optimal measuring points is proposed. By construction of the suitable error vector and its corresponding error transformation matrix, the optimization criterion in robotic area is adopted to evaluate the identification effect of the measuring points. Based on the optimization criterion, the scheme of the measuring points selection can be established. The method proposed is validated by a case study. The method can help increase both the measurement efficiency and the error identification effect.