bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Tire Wear on Wear Rate
Authors: Brenner F. C. , Scheiner S. R. , Kondo A.
Published: June 2006

A question arises as to whether the wear rate of tires is constant under constant conditions and whether the tread life of tires may therefore be projected by linear extrapolation from low mileage tests. A second question arises as to whether commercially produced tires are uniform enough to serve as monitors of environmental change. A third question concerns the specific method of estimating the wear rate. This paper reports the results of experiments conducted on the National Highway Traffic Safety Administration test course designed to supply data relating to these questions. Regression of average groove depth against mileage for each of 27 tires gave a straight line which accounted for over 99% of the variability with a standard deviation of about 2 mils. Tread life projected from a 6400-mile (10 300-km) test gave on the average the same tread life as projected at higher mileages. A bias tire built under stringent quality control specifications and the radial tire selected for monitoring environmental effects were very homogeneous. The bias and belted bias course-monitoring tires were more variable.

Various methods of estimating the wear rate and use of the multiplicative model (requiring geometric means) for analysis for factor effects are discussed. The regression line method is chosen for tire rating.
A Note on Skid Resistance and the Road Profile
Authors: Williams H.
Published: June 2006

This report summarizes skid resistance information from many sources throughout the United States in an effort to determine whether surfaces with skid numbers below 35 should be used in traction grading. The author recommends that a constant inventory of pavement skid resistance be maintained to determine repair priorities and that a slippery surface (skid number in the range 20–25) be included in a test procedure for tire traction grading.
Energy Loss of Pneumatic Tires Under Freely Rolling, Braking, and Driving Conditions
Authors: Schuring D. J.
Published: June 2006

The concept of rolling resistance force is replaced by that of energy dissipated in unit distance traveled. The energy loss per unit distance, which is a function of slip angle, inclination angle, wheel torque, and other variables, is shown to reach a minimum under driving conditions. The new formula is compared with those given by Gough and by the Society of Automotive Engineers.
Interlaboratory Groove Depth Measurements and Wear Estimation
Authors: Kondo A. , Brenner F. C.
Published: June 2006

A tire was measured to determine its average groove depth by each of several operators in each of seven laboratories in the morning and afternoon for two consecutive days. The results show that the operators repeat their measurements within acceptable variation. On averages of six measurements by a single operator, a difference of 0.002 in. (0.05 mm) was significant. The variability of operators' averages around their laboratory average was the same for all laboratories except one. However, averages among laboratories were different, which is attributed to small differences in the measuring practice. The precision of wear rate estimates based on the difference of average groove depths before and after a period of wear is estimated and ways in which the precision of estimates of wear rates can be optimized are suggested.
On the Inflated Tire Profile: Inflation and Axial Compression of a Composite, Initially Cylindrical Membrane
Authors: Nicholson D. W.
Published: June 2006

The analysis for the inflation of bias tires, based on the model of the net of inextensible cords, is reformulated in terms of bead point coordinates and the cross angle of cords in the initially cylindrical membrane. A simple numerical method of solution is described. An exact solution in a special case is given. Computations are presented for maximum cord tension, maximum cord-rubber shear stress, and bead tension.
Temperature Rise Times in Pneumatic Tires
Authors: Clark S. K.
Published: June 2006

An idealized model is proposed for heating of a pneumatic tire. A solution is obtained for the temperature rise of such a model. Using known thermal properties of rubber and known heat transfer coefficients, the time to reach thermal equilibrium is estimated.
On Viscoelasticity and Standing Waves in Tires
Authors: Padovan J.
Published: June 2006

Based on the classical ring on foundation model for the tire, the effect which structural damping has on the development of the standing wave phenomenon is investigated. In particular, the model employed consists of a rotating ring on foundation where, in addition to including Coriolis effects, Kelvin-Voigt-type viscoelasticity is admitted in both the ring and foundation. Enforcing strict periodicity in space and time, the exact solution is obtained to the stated problem. Several parametric numerical experiments employing this solution are reported. These demonstrate that the standing wave phenomenon in tires is essentially a viscoelastic-type resonance response.
A Note on Repeatability of a Fifth Wheel
Authors: Williams H.
Published: June 2006

This report describes an experiment to determine the length of a tread wear course and the repeatability of two fifth wheels used to make the measurement. The position of the fifth wheel in the convoy of four vehicles does not contribute significantly at the 95% level of confidence, nor does the difference in wheels. The course measured 397.749 miles (640.115 km) with a standard deviation of 0.115 miles (0.185 km).
A Note on the Classical Net Analysis of the Inflated Tire Profile
Authors: Nicholson D. W.
Published: June 2006

It is shown that the classical model for the inflation of bias ply tires, which is based on the assumption of a net of inextensible cords, only permits convex profiles. Otherwise, the equations of the classical model involve complex quantities.
A Note on Tire Rolling Resistance Due to Test Wheel Curvature
Authors: Bekker M. G. , Semonin E. V.
Published: June 2006

Tire rolling resistance is affected by laboratory drum diameter. Such tests produce higher rolling resistance values than road testing. Semi-empirical formulae were developed to correlate tire behavior on a test drum with wheel-road systems analysis, and the geometry of the tire and test drum were analyzed.
Lateral Tire Forces on Wet Roads
Authors: Schallamach A.
Published: June 2006

Expressions are derived for side force and self-aligning torque of a simple tire model on wet roads with velocity-dependent friction. The results agree qualitatively with experimental results at moderate speeds. In particular, the theory correctly predicts that the self-aligning torque can become negative under easily realizable circumstances. The slip angle at which the torque reverses sign should increase with the normal load.
Tread Life of Original Equipment Radial Tires
Authors: Root B. W.
Published: June 2006

In 1976 tread wear was surveyed in 24 cities within the contiguous 48 states and in Fairbanks, Alaska. Each tire, exclusive of spares, was gaged for tread depth at two circumferential locations in three grooves: inner shoulder, center, and outer shoulder. The corresponding odometer reading was recorded. A national pattern of variation in tread life expectancy was revealed. Variation attributable to brand, size, vehicle, and wheel position was also found.
Energy Loss in an Analytical Membrane Tire Model
Authors: Tielking J. T. , Schapery R. A.
Published: June 2006

Energy dissipation is calculated from the contact deformation of a rolling toroidal membrane tire model. The method of dissipation analysis developed here can be used with other structural representations, including those based on the finite element method. The membrane tire model is inflated, loaded, and rolling on a frictionless, flat surface. The membrane material is assumed to be isotropic and neohookean under static loads and to exhibit a low loss tangent. The assumption of a low loss material permits viscoelastic power loss to be calculated from load transfer functions derived from the elastic response of the tire model. The power loss calculation is used to predict rolling resistance and contact patch shift.
A Note on the Accuracy of Calibration of a Fifth Wheel
Authors: Williams H.
Published: June 2006

A series of experiments were carried out using a fifth wheel to determine how accurate the wheel was when using different calibration methods. The methods are described and the results analyzed to determine the effects of method and speed. It was found that the methods of calibration were not significantly different but the tests were speed-dependent.
Laser marginal lap microwelding for ultrathin sheet metal
Authors: Du J. , Longobardi J. , Latham W. P. , Kar A.
Published: June 2006

Butt welding is practically difficult for sheet metals as thin as 50–100 μm. A new concept called marginal lap welding is developed in this study to produce continuous and distortion-free welds for such thin sheets. The energy loss due to heat conduction into the clamps becomes significant under this situation, and therefore, the input laser power to produce an effective weld increases. This article investigates the effects of heat loss during marginal lap welding of ultrathin stainless-steel (SS316L) sheets experimentally and theoretically. A mathematical model is developed to calculate the amount of conduction heat loss and the weld geometry. The results show that a smaller clamp gap causes more heat loss into the clamps and generates a narrow heat-affected zone, which is found to be beneficial to the corrosion resistance of the weldment.
Experimental study on surface decontamination by laser ablation
Authors: Zhou X. , Imasaki K. , Furukawa H. , Yamanaka C. , Nakai S.
Published: June 2006

A high-power pulsed Nd:YAG laser was employed to irradiate a 20-μm-thick Zn coating on a carbon steel surface. The ablation rate was defined as ablated volume divided by consumed laser energy, and was used to assess ablation cleaning ability. The relationships of ablation rate to laser pulse width and ablation rate to laser fluence were investigated, and optimal processing conditions were determined. The influence of incident laser angle on ablation rate was not considerable as the angle was within 90°–20°. The behavior of the laser-induced products was studied. It was found that the products consisted of vapor and liquid particles, and that the moving direction of these particles was strongly dependent on incident laser angle. A smaller incident laser angle provided the focusing lens better protection from the pollution of the ablated products. Microprofile measurements and composition analyses were performed to estimate the cleaning effects of laser ablation. Results show that the Zn coating was removed completely and satisfactory cleaning was obtained.
Cutting of slate tiles by CO2 laser
Authors: Boutinguiza M. , Lusquiños F. , Pou J. , Soto R. , Quintero F. , Pérez-Amor M. , Watkins K.
Published: June 2006

Slate is a natural stone which has the characteristic that shows a well-developed defoliation plane, allowing to easily split it in plates parallel to that plane which are particularly used as tiles for roof building. At present, the manufacturing of slate is mostly manual, being noisy, powdery, and unsafe for the worker. Thus, there is a need to introduce new processing methods in order to improve both the working conditions and the quality of the products made of slate. Following previous work that focused on the drilling and cutting of slate tiles using a Nd:YAG laser, we present in this article the results of the work carried out to explore the possibilities to cut slate plates by using a CO2 laser. A 1.5 kW CO2 laser was used to perform different experiments in which the influence of some processing parameters (average power, assist gas pressure) on the geometry and quality of the cut was studied. The results obtained show that the CO2 laser is a feasible tool for successful cutting of slate.
Phosphoric acid activated surface modification of tooth dentine by 9.45 μm transversely excited atmosphere CO2 laser
Authors: Awazu Kunio , Tanaka Mikio , Kato Junji
Published: June 2006

Tuning a laser wavelength to the stretching vibration of specific biomolecules has some advantages in ablating hard tissue and for surface modification induced by the photothermal or the photomechanical interaction. A tunable pulsed transversely excited atmosphere CO2 laser was tuned to 9.45 μm, which is the stretching vibration of phosphoric acid in hydroxyapatite. Dried cow dentine was irradiated at 36 W/cm2. The infrared absorption spectra of the bovine dentine sample were measured using a microscopic Fourier-transform infrared (FTIR). After laser irradiation, x-ray fluorescence of elements contained in a 300 μm×300 μm irradiated area was measured by energy dispersive x ray (EMAX-5770). This laser irradiation reduced the peak wavelength of the dentine surface from 9.76 to 8.93 μm. The atomic ratio of Ca/P was changed from 1.4 to 1.9 as measured with x-ray diffraction. These results show the potential for application of a 9.45μm CO2 laser to ablation and modification of the dentine surface as measured by FTIR absorption microscopy.
Particle size analysis of material removed during CO2 laser scabbling of concrete for filtration design
Authors: Lobo L. M. , Williams K. , Johnson E. P. , Spencer J. T.
Published: June 2006

This article examines the particles formed during optimized laser scabbling of concrete in order to help determine an effective filtration strategy for the process. The laser scabbling technique has been developed for noncontact removal of radioactive contaminated surface concrete layers. Surface layer removal is effected using a high power carbon dioxide laser beam to generate stresses in the substrate (caused by temperature gradients and dehydration) which break up the surface. The material removed will be contaminated with radionuclides and its efficient collection must be ensured to prevent the escape of radioactive contaminated particles. The filtration methods selected depend on the size of the particles produced and transport characteristics in an airflow. The particles removed were examined using a laser diffraction particle sizer (for particles below 80 μm physical diameter) and sieving (above 150 μm physical diameter) to determine the particle size distribution. Scanning electron microscope (SEM) analysis was used to identify the components present. The study found that particles removed were constituents of the parent concrete, there were no signs of melting and a small volume fraction (less than 1%) of sub-100 μm physical particle diameter. Particles with aerodynamic diameters under 100 μm are airborne and those between 1 and 30 μm are inhaled into the thoracic and bronchial tracts and lungs. Efficient filtration is required to capture these particles. However, filtration is difficult in the 0.1–1 μm aerodynamic diameter range, which comprises only 0.02% by volume of the removed material. It is considered that laser scabbling of concrete using this method will produce no additional risks than the use of other surface removal mechanisms.
Multiple reflection and its influence on keyhole evolution
Authors: Ki Hyungson , Mohanty Pravansu S. , Mazumder Jyotirmoy
Published: June 2006

In laser drilling and keyhole welding, multiple reflection phenomena determine how the energy is transferred from the laser beam to the workpiece, and, most importantly, all other physics such as fluid flow, heat transfer, and the cavity shape itself depend on these phenomena. In this study, a multiple reflection model inside a self-consistent (or self-evolving) cavity has been developed based on the level set method and ray tracing technique. In the case of drilling, it is observed that the laser energy tends to concentrate near the center, where the effective intensity reaches a value two orders of magnitude higher than the original distribution. In keyhole welding, however, the maximum laser intensity is only around five times higher than the original during the entire process. Combined with the strong keyhole fluctuation, the redistributed intensity patterns are very dynamic. The intensity fluctuation drives the keyhole fluctuation, and the keyhole fluctuation, in turn, affects the intensity fluctuation. This study demonstrates that drill holes are highly efficient surfaces to focus a large amount of energy in a tiny area while keyholes have the capacity to evenly distribute the energy in a large area. It is also shown that multiple reflection phenomena are highly geometry dependent and a preassumed hole shape as adopted in many prior studies may lead to an inappropriate result.
Melt instabilities during laser surface alloying
Authors: McCay M. H. , Hopkins J. A. , McCay T. D.
Published: June 2006

The depth of the melt layer during laser surface alloying plays a significant role in the shape of the melt pool. There appear to be critical depths at which the molten layer becomes unstable and alters its shape in response to convective flow patterns. The Marangoni number provides an understanding of the influence of the material properties on convection and subsequently the melt shape, being inversely proportional to depth squared, viscosity, and thermal diffusivity, and directly proportional to the surface tension gradient. The laser processing parameters affect the melt shape through their influence on depth. The current research sought to influence the Marangoni flow and control the shape of the melt pool using a rectangular beam.
An investigation of rapid prototyping of sand casting molds by selective laser sintering
Authors: Casalino G. , De Filippis L. A. C. , Ludovico A. D. , Tricarico L.
Published: June 2006

Among the layer fabrication techniques, selective laser sintering (SLS), is widely used for manufacturing various products made of different materials (i.e., polycarbonates, nylons, polyamides, sand casting, metal powders, and others). The SLS of precoated foundry sands allows the aggregation of adjacent particles, which are then cemented by furnace heat treatment. Moreover, geometrically complex molds and cores not obtainable with conventional methods can be realized by this method. In this article, the optimization of laser parameters is reported for fabricating transitory molds for foundry applications. Lasercron sand, a quartz sand with a thin phenolic resin coating often used for SLS applications, was tested. The CO2 and diode lasers were used for this study. After some preliminary tests, experimental design techniques were applied to investigate the influence of some processing parameters, i.e., laser power, scan speed, and scan spacing (hatch). Their interactions were evaluated using response surface methodology and analysis of variance. The laser irradiation effects on the adhesion between grains and layers, the quality and accuracy of the surfaces, and the sintered thickness were evaluated. The optimum combinations of processing parameters were selected and the operating window was defined. Simple cylindrical-shaped specimens were fabricated as a validation of that window.
Monitoring of laser weld penetration using sensor fusion
Authors: Sun Allen , Kannatey-Asibu Elijah , Gartner Mark
Published: June 2006

Depth of penetration is a critical parameter in laser welding. In many applications, full penetration is desired, but difficult to detect in real time. A sensor fusion system using infrared, ultraviolet, audible sound, and acoustic emission has been implemented for real time monitoring of CO2 laser lap welds in both laboratory and industrial production settings. Signals from the welds were analyzed by: (1) singular value decomposition with data fusion, (2) class mean scatter with decision fusion, (3) class mean scatter with feature fusion, and (4) singular value decomposition with decision fusion using minimum distance and quadratic classification. A classification rate of 100% was obtained for detection of full penetration for both laboratory and production settings.
Influence of oxide film on weld characteristics of mild steel in CO2 laser welding
Authors: Ono Kazuhiko , Adachi Kaoru , Miyamoto Isamu , Inoue Takashi
Published: June 2006

The influence of oxide film, such as laser cutting edge or mill scale, on CO2 laser welding phenomena and weld characteristics of mild steel was investigated. Laser welding of butt joints, which were different in location and thickness of oxide film, were performed. Examinations were made on the weld characteristics which were: bead geometry, defect, and microstructure. Light emitted from laser induced plasma was also analyzed to understand welding phenomena. The results of these experiments lead to understanding that oxide film, especially on the joint face, causes substantial spatters, an underfilled surface, the disappearance of the nail head, porosity formation, and reduction of hardness. It is considered that these are attributed to oxygen, which reduces surface tension of molten metal and reacts with carbon, manganese, and silicon. These results suggest that reduction of oxide film thickness or killing oxygen activity by supplementary deoxidizing elements may produce acceptable weld.
Energy redistribution during CO2 laser cladding
Authors: Gedda H. , Powell J. , Wahlström G. , Li W.-B. , Engström H. , Magnusson C.
Published: June 2006

This article examines the factors that effect the efficiency of the CO2-laser powder cladding process. By theoretical calculation and experimental work it has been possible to identify how much of the original laser energy contributes to the cladding process and how much is lost to the surrounding environment by reflection, radiation, convection, etc. Every aspect of energy redistribution has been analyzed and quantified and this has led to a deeper understanding of the process. The article concludes with a number of suggestions for improving the efficiency of blown powder laser cladding.
Application of 7 kW class high power yttrium–aluminum–garnet laser welding to stainless steel tanks
Authors: Shimokusu Yoshiaki , Fukumoto Seiji , Nayama Michisuke , Ishide Takashi , Tsubota Shuho , Matsunawa Akira , Katayama Seiji
Published: June 2006

Laser beam welding is used for precise parts such as core internal parts in nuclear power plants that require high quality. To weld large-scale and thick-wall products, the high power laser beam must be transferred and a deep penetration welding procedure must be developed. In this article, therefore, an optical fiber transmission system for 7 kW class high power yttrium–aluminum–garnet (YAG) laser and pulse modulated laser welding techniques were developed to obtain deep penetration. The detailed observation of the weld pool and keyhole dynamics using a high-speed camera and x-ray transmission system was carried out to understand high power YAG laser welding phenomena. It has been clarified that there are proper pulse duty and pulse duration for optimum welding condition to obtain sound and efficient weld. After confirmation of the high power YAG laser welding joint performance, this procedure has been applied to the welding of stainless steel tanks for the nuclear fuel reprocessing plant.
Thermomechanical effects in laser microprocessing for dieless metal wire drawing
Authors: Li Yonggang , Quick Nathaniel R. , Kar Aravinda
Published: June 2006

A new dieless metal fiber drawing process is developed in which a high-precision laser is used to heat the precursor wire to its superplastic temperature. The advantages of this technique over conventional cold drawing include larger diameter reduction ratio, no dies and lubricants, and the flexibility to draw fine wires of different diameters with the same apparatus. It is a promising process for the fabrication of fine wires that are difficult to draw with conventional processes or that require a high-quality surface without any contamination. The temperature profile generated by laser heating is critical in determining the plasticity and deformation behavior of the wire during the drawing process. The coupled thermomechanical problem is solved numerically for the temperature distribution and wire diameter reduction. Commercially pure nickel wires of initial diameter 125 μm are used as samples for laser drawing experiments, and the experimental results are compared with the model predictions. The wire drawing setup also provides a novel apparatus for evaluation of mechanical properties at high temperatures.
Deformation behavior and microstructural changes of a hardened high carbon alloy steel in laser bending
Authors: Chan K. C. , Liang J.
Published: June 2006

In this article, the deformation behavior and microstructure of a hardened high carbon steel in laser bending were examined. A CO2 laser unit (TEM00) was used to bend the samples at different laser powers, scanning velocities, and number of scans. A relatively linear relationship between bending angle and number of scans was obtained at laser powers of 150 and 200 W and at a scanning velocity of 30 mm/s. A threshold heat input of about 3.25 J/mm was observed, below which bending was unlikely to occur. The bending angle was also found to increase linearly with increasing line energy and was sensitive to specimen width. The microstructure and microhardness profile of the sheets deformed at both low- and high-energy inputs were examined. For accumulated energy density (AED) of 193 J/mm2, melting was observed at the scanning surface and the microstructure was different significantly across the thickness of the bent region. A microstructure of coarse martensite with retained austenite was observed near the top surface, whereas martensite with retained carbide and banite was found near the bottom surface. For AED of 97 J/mm2, no melting was observed, and tempered martensite could be found at the bottom surface of the bent region.
Characterizing keyhole plasma light emission and plasma plume scattering for monitoring 20 kW class CO2 laser welding processes
Authors: Tu J. , Miyamoto I. , Inoue T.
Published: June 2006

In very deep penetration, the plasma inside the keyhole exhibits complicated behavior and the plasma plume covering outside the keyhole can also affect the observation of keyhole plasma. Measuring the light emission from keyhole plasma is an effective method to monitor laser welding processes in thin sheets; however, in welding thick sheets, several critical phenomena must be observed. In this article, we provide experimental investigations using a 20 kW CO2 laser to characterize the wavelength contents of the keyhole plasma light emission. We also demonstrate that the plasma plume outside the keyhole can scatter the light emission from the keyhole plasma significantly. A scattering model is proposed and verified experimentally. The particles responsible for scattering are also identified.
Effects of laser welding parameters on magnetic materials with the aid of a mechatronic measuring system
Authors: Abdullah Hussein A. , Chatwin Chris R.
Published: June 2006

This article reports results from an experimental investigation into laser welding of ferromagnetic material, which, for example, is of interest to the European Space Agency. The effects of laser welding power and translation velocities on the magnetism of ferromagnetic materials were studied. An automated system using a Hall effect transducer was constructed to measure the magnetic field transverse to the laser weld before welding, immediately after welding and three days after welding. The results show that immediately after welding the magnetization of the melt pool and heat affected zone are decreased, with the greatest decrease occurring in the weld. Interestingly, after a period of three days, during which the samples were isolated, the magnetization in the area adjacent to the weld had recovered. Specimens of iron magnet were used for the experiments; Ferranti’s MFKP 1.2 kW CO2 and GSI Lumonics Nd3+ yttrium–aluminum–garnet (YAG) lasers were utilized to weld the specimens. From both Nd3+ YAG and CO2 laser welding results, it can be concluded that at high workpiece translation speeds an optimized laser power should be used in order to minimize the size of the demagnetized zone. We also found that the specimens welded with the Nd3+ YAG pulsed laser show a better remagnetization rate and recovery than the specimens welded with the continuous wave CO2 laser.
Pulsed laser driven deposition of spattered molten particles and its application to the manufacturing of wear-resistant coatings
Authors: Nagai Toru , Inoue Takashi , Shimura Hirofumi
Published: June 2006

In this article, we report on a new process for manufacturing metal coatings with submillimeter thickness by pulsed laser driven deposition of molten metal particles. The process of “laser spattering of molten particles” using a high pulse-energy laser is considered to be effective compared to the conventional physical vapor process based on vaporized ultrafine particle generation in vacuum, because the energy required for melting the material is much lower than that for vaporizing it. In this process, the substrate is irradiated with another laser to obtain a close coating and various hard layers in it. We studied the productivity of spattered molten particles of metals (Fe, Ni, Cr, Cu, Mo, and W), and the morphology of the coatings. We applied this process to the manufacturing of wear-resistant coatings such as cast iron–molybdenum compound coatings. They showed good wear characteristics.
Antigalling and low friction properties of a laser processed Co-based material
Authors: Persson D. H. E. , Jacobson S. , Hogmark S.
Published: June 2006

The antigalling and low friction properties of a CO2-laser processed Co-based material (Stellite 21) was investigated under high-load sliding conditions. Dry sliding tests were carried out at both room temperature and at 250 °C. The tests were performed by sliding two identical specimens against each other in a dedicated test. A low and stable friction coefficient at a level of about 0.20, and relatively independent on load and sliding speed, was obtained after a short running-in period. No tendency to galling was observed in any test. During sliding, the superficial face-centered-cubic material transforms to hexagonal-close-packed with the {0001} planes preferentially orientated parallel to the surface of the wear track. Since these planes are easily sheared, and supported by a deformation hardened zone, a surface layer is generated with low friction properties and high resistance to galling. Thus, the laser processed Co-based alloy exhibits the functional ability to generate a surface with unique properties during sliding contact.
Determining source size from diode laser systems
Authors: Marshall Wesley J.
Published: June 2006

Although hazard classification is performed at predefined distances, the maximum permissible exposure (MPE) for extended-source diode lasers decreases as the distance from the laser increases. The MPE depends on the apparent angular subtense of the source, which is simply the magnified image of the emitting diode. Small diameter beams require special consideration.
High-energy femtosecond pulsed laser micromachining of thin film deposited silicon in self-focused air medium
Authors: Dong Yuanyuan , Molian Pal , Zorman Christian , Mehregany Mehran
Published: June 2006

The ultrashort pulsed laser ablation of silicon wafers deposited with 1 μm thin film of SiC was performed in air medium using a 1 mJ, 120 fs, 800 nm Ti:sapphire laser, the objective being to determine the self-focusing capability of air to produce nanostructures. The effects of pulse energy, the number of pulses, pulse repetition rate and x–y translation speed on the size, shape, and thermal damage of holes and grooves were evaluated. In addition, a 200 ns pulsed, 1064 nm Nd:yttritium–aluminum–garnet laser was used to process grooves and the results were compared against those processed by the femtosecond pulses. Results show that holes as small as 1 μm were produced with femtosecond pulses using the self-action property of air. Despite the capability of air medium to produce tiny holes of a few micron diameters, the shape of the hole is highly asymmetrical due to the beam profile distortion. The critical laser power for nonlinear effects of air to become effective was calculated as 40 MW. However, both the beneficial and deleterious effects of air were not found when the peak power of laser beam was under 2 GW. A comparison of femtosecond pulsed laser ablation with nanosecond pulsed laser ablation demonstrated the advantages of small size, minimal thermal damage and cleanliness for ultrashort pulses.
Automatic detection of lack of fusion defects in CO2 laser gear welding
Authors: Ghasempoor A. , Wild P. , Auger M. , Mueller R.
Published: June 2006

Laser welding is becoming increasingly important in the automotive industry and quality of the weld is critical for a successful application. In many cases the increase in welding speed provided by laser welding has resulted in the need for an automated, on-line weld monitoring system. This article describes a methodology for monitoring laser gear welding with the objective of detecting lack of fusion defects. The proposed system is evaluated experimentally. It is also shown that the proposed signal processing and modeling technique can be used to detect porosity in the welds.
Copper vapor laser micromachining of 304 stainless steel
Authors: El-Bandrawy M. , Nagarathnam K. , Gupta Mool C. , Hamann C. , Horsting J.
Published: June 2006

A copper vapor laser (CVL) of 511/578 nm wavelength, 25 ns pulse width, and 10 kHz repetition rate combined with a computer controlled galvo head was used for laser micromachining of 304 stainless steel. The objective of this study was to develop the CVL micromachining process and its optimization. We observed a significant improvement in micromachining quality with a spatially filtered beam. Micromachining experiments were carried out on stainless steel strip samples of 75, 153, and 356 μm thickness. We studied the ablation rate using a single pulse and monitored the heat affected zone (HAZ) as a function of the applied laser power density. The ablated volume and HAZ are directly proportional to the applied laser power density for low to medium laser powers (up to 2×1013 W/m2). The ranges of HAZ diameter and ablated volume were 15.3–28.7 μm and 112.8–537.6 μm3, respectively, for the applied power density in the range of 1.0–63.7×1013 W/m2. The roughness created by ablation process was studied at various pulse overlaps at laser power density of 87.8×1013 W/m2. Ablation depth and surface roughness were found to be inversely proportional to the center-to-center pulse overlap and directly proportional to the power density.
Dual laser beam modification of high alumina ceramics
Authors: Triantafyllidis D. , Bernstein J. R. , Li L. , Stott F. H.
Published: June 2006

Alumina-based refractory materials are extensively used in high-temperature applications, such as linings in waste incinerators. A significant problem affecting the performance of these materials is the presence of porosity and material inhomogeneity, which promote molten slag corrosion and chemical degradation. Single laser energy sources have been used in the past to densify and homogenize the surface of such ceramics. A major difficulty during laser surface treatment of brittle materials, such as ceramics, is solidification cracking due to very large temperature gradients that are developed during processing. The aim of the work presented in this article is to investigate the surface modification of 60% alumina refractory ceramics by applying two laser sources simultaneously in order to control the thermal gradients and cooling rates so that crack formation can be eliminated. The dual laser beam modified surfaces have been analyzed using optical and scanning electron microscopy, as well as electron probe microanalysis, and compared with those of single laser beam treated samples.
Laser penetration spike welding: A microlaser welding technique enabling novel product designs and constructions
Authors: Dijken D. K. , Hoving W. , De Hosson J. Th. M.
Published: June 2006

A novel method for laser penetration microspot welding of sheet metal is presented. With this so called “laser spike-welding,” large gap tolerances are allowed. Depending on the ratio of laser spot radius to top plate thickness, gaps of 100% of the top layer thickness and more can be bridged. With conventional keyhole penetration welding this is only 20%–40% at most. So, with spike welding the gap between the metal plates can be increased by a factor of 2.5–5. In this way a powerful and attractive welding technique for joining of thin metal plates is available. The laser spike weld method can handle larger production tolerances and will enable novel and cheap product designs and welding of dissimilar materials.
Laser surface processing of titanium in air: Influence of scan traces overlapping
Authors: Pérez del Pino A. , Serra P. , Morenza J. L.
Published: June 2006

Laser surface treatments of titanium in air have been performed through a pulsed Nd:yttrium–aluminum–garnet (λ=1.064 μm) laser. Several samples have been obtained modifying the laser scan velocity and partial overlapping of consecutive traces, in order to study the influence of these parameters on the surface morphology. Scanning electron microscopy and profilometry measurements have revealed different surface morphologies depending on the physical processes involved in the treatments. The surfaces are melted in all cases and present a different crack configuration depending on the melting regime. In addition, at low scan velocities, the presence of a laser generated plasma results in a periodic groove structure that evolve to a flat and porous surface when the distance between traces is decreased.
Experimental and numerical analyses of the mechanism for decreasing hydrogen-embrittlement sensitivity of aged Inconel 718 by laser surface annealing
Authors: Liu Liufa , Tanaka Katsumi , Hirose Akio , Kobayashi Kojiro F.
Published: June 2006

Laser surface annealing (LSA) treatments were conducted to decrease the hydrogen embrittlement (HE) sensitivity of Inconel 718. Hydrogen was charged into the alloy by a cathodic-charging process. The LSA treatment significantly reduced the strength loss of the hydrogen-precharged notched specimen. Tensile tests and elasto–plastic simulations were performed to study how LSA affects the HE sensitivity of the as-aged Inconel 718. Various heat treatments were applied to the notched tensile specimens to obtain different precipitation states of γ″. All tensile tests were conducted in air at room temperature under identical conditions. One specimen of each kind was free of hydrogen; another was charged with hydrogen prior to the tensile test. A correlation between the HE sensitivity and the precipitation state of the alloy was confirmed by assessing the loss in the notch tensile strength due to hydrogen pre-charging. The γ″ particles, especially those in the surface layers, were proved to have deleterious effects on the HE sensitivity of Inconel 718. Fractures originated from the surface vicinity in the as-aged specimen when there was precharged hydrogen. However, hydrogen-induced fractures in the LSA-treated specimen originated in the deep region of the laser-annealed surface layer. Stress concentration conditions at the notch roots were studied via elasto–plastic finite element method simulations. The area of most highly concentrated stress of the LSA-treated specimen was in deep layer of the laser-annealed notch region where the material was partly annealed. The formation of the annealed surface layer that has better HE resistance than the as-aged alloy, and the migration of the fracture origin to deeper layers were considered to be the mechanism for decreasing the HE sensitivity by the LSA. Further, the partly annealed raw alloys with strength comparable to the LSA-treated specimens were found to have much higher HE sensitivities than the corresponding LSA-treated specimens. Both the experimental results and the simulation results suggested that the LSA caused the fracture origins to migrate from surface to deep layers. It is possible to reduce the HE sensitivity of Inconel 718 without sacrificing its strength by applying LSA to produce locally annealed surface zones.
Excimer laser fabrication of polymer microfluidic devices
Authors: Kim Joohan , Xu Xianfan
Published: June 2006

Silicon has been a primary material for fabrication of microelectromechanical systems (microfluidic devices in MEMS) for several decades. This is due to the fact that the MEMS techniques were derived from those used for microfabrication in the semiconductor industry. These techniques are well developed, and can be readily applied for silicon based MEMS fabrication. Nowadays, alternative manufacturing materials and techniques are needed for reducing costs and meeting new requirements. Polymers have many advantages because of their low costs and applications in microfluidics. This article describes processes for fabricating polymer-based MEMS, including machining and bonding techniques. Microfluidic parts are machined on polymers with a KrF excimer laser (λ=248 nm). Mask patterning and direct laser writing techniques are used. A silicon-on-glass process and an infrared laser bonding process are applied to assemble the machined parts with transparent cover glasses or plastics. As an example, a polymer micropump is fabricated and tested. It is shown that with the use of polymer materials, the performance of the pump is greatly improved.
Selective decolorization of pigments within two and three pigmented inks for colored marking by a Q-switched laser
Authors: Stewart R. , Li L.
Published: June 2006

Inks consisting of two and three pigments as well as an infrared absorber were printed onto plain paper and treated using a Q-switched Nd:yttrium–aluminum–garnet laser. It has been shown that the color of these inks can be altered through selective pigment decay: a red, green and blue ink decayed red first, then green, leaving a blue mark or a purple one, selectively. The process is related to the thermal decomposition temperature of the pigments used which is dependent upon the incident laser intensity.
Preparation of polyperinaphthalenic organic semiconductive nanoparticles by excimer laser ablation and their application to optic and electronic devices
Authors: Nishio Satoru , Fukumura Hiroshi , Tamura Kazuyuki , Murata Jun , Kitahara Junko , Kan Teruhiko , Matsuzaki Akiyoshi , Ando Nobuo , Hato Yukinori
Published: June 2006

Polyperinaphthalene (PPN) nanoparticles are prepared by excimer laser ablation (ELA) of a 3, 4, 9, 10-perylenetetracarboxylic dianhydride (PTCDA) target or a mixture target of PTCDA with Co or TiO2 powder (PTCDA/X: X=Co, TiO2) using XeCl excimer laser beams. Enhancement of elimination reaction of side groups of PTCDA is observed by ELA of PTCDA/Co and PTCDA/TiO2. In particular, for PTCDA/TiO2, the reaction occurs at a fluence of 0.25 J cm−2 pulse−1 much lower than the case of PTCDA/Co at room temperature. Heterojunctions between the PPN nanoparticle layer and Si wafers are formed. Well rectifier property is demonstrated for the junction with n-Si substrates. Current versus voltage curve of the heterojunction with a n-Si substrate in the dark and under illumination shows the possibility of the junction as a photovoltaic cell. Furthermore, PPN nanoparticles are applied to anode electrodes for ultrathin rechargeable Li ion batteries. In situ Raman spectroscopy under lithium ion doping is performed to elucidate the storage mechanism of lithium ion at cis-polyacetylene-type edge (phenanthrene-edge) of PPN structure.
Condition monitoring and lifetime estimation of a CO2 laser
Authors: Koomsap P. , Prabhu V. V. , Shaikh N. I. , Schriempf J. T. , McDermott J. H.
Published: June 2006

Lasers are being successfully applied to a variety of manufacturing processes, including cutting, welding, cladding, and free forming. Part of their success is due to the high quality beam that is directly related to the condition of components involved in the lasing process. However, maintaining the requisite beam quality requires frequent and time-consuming intervention by maintenance operators, specifically, for dismounting, inspection, servicing, and reassembly. Preventive maintenance, targeting reduction of machine downtime by prevention of faults, is the de facto maintenance program for lasers in industry. In this work, condition monitoring and lifetime estimation have been proposed to enable predictive maintenance programs for CO2 lasers. Specifically, the cooling system of a CO2 laser is monitored to infer its health condition, which is then used to statistically predict its lifetime. A Weibull distribution has been used to model the hazard function that depends on the operating parameters and the condition of the machine. The monitoring and estimation strategy has been verified using simulation. Results of tests conducted at Applied Research Laboratory (ARL) at the Pennsylvania State University to exemplify the proposed approach are also presented.
Steel microstructures in autogenous laser welds
Authors: McPherson N. A. , Samson H. , Baker T. N. , Suarez-Fernandez N.
Published: June 2006

Autogenous Nd:YAG laser welding was carried out on austenitic stainless steel (316LN) and duplex stainless steel (2205). The structures were examined using optical and color etching metallography. This showed optically that the austenitic steel solidified as a totally austenitic structure, but the transmission electron microscopy (TEM) work confirmed the presence of ferrite. In the case of the duplex stainless steel, the solidification structure was almost 100% ferrite. However, the weld metal properties required were met. Dissimilar autogenous Nd:YAG laser welding was performed on a duplex stainless steel to carbon steel joint and on an austenitic stainless steel to carbon steel joint. This revealed the presence of preferential fluid flow to the stainless steel side in the weld metal, and areas of excessive hardness. The results of this study were that filler wire would be required to counteract the high hardness effects induced by the autogenous laser welding process, without having to resort to postweld heat treatment. An evaluation has also taken place of autogenous CO2 laser welds of D and DH 36 steel. Mechanical properties of the DH 36 steel have been found to be acceptable, and the structure of the D grade material has been examined using TEM, where pearlite and bainite have been identified as being present.
Solution of two-temperature thermal diffusion model of laser–metal interactions
Authors: Vatsya S. R. , Virk Kuljit S.
Published: June 2006

The two temperature coupled equations, modeling thermal diffusion during laser-induced ablation of metals, are solved under the assumptions that the electron and the lattice heat capacities, and the thermal conductivity remain constant in the process. In view of its practical value, the solution is initially obtained for the energy sources with a Gaussian distribution. The solution is then generalized to include a larger class of source terms for comparison with other results. Present analysis is valid under less restrictive conditions than frequently imposed in the literature. In particular, the solution is valid for realistic source terms and describes the process for ultrashort to nanosecond pulse-width regimes. More general results obtained here retain the attractive features of other approximate solutions available elsewhere and reduce to them under the respective conditions. Predictions of the present model agree well with the experimental observations reported in the literature.