The Effect of Laser Ablation Pulse Width and Feed Speed on Necrosis and Surface Damage of Cortical Bone

Bone cutting is of importance in orthopaedic surgery but is also challenging due to its nature of brittleness—where severe mechanical and thermal damages can be introduced easily in conventional machining.Laser machining is a new technology that can allow for complex cut geometries whilst minimising surface defects i.e.,smearing,which occur in mechanical methods.However,comparative studies on the influence of lasers with different pulse characteristics on necrotic damage and surface integrity have not been reported yet.This paper for the first time investigates the effects of laser type on the necrotic damage and surface integrity in fresh bovine cortical bone after ex-situ laser machining.Three lasers of different pulse widths,i.e.,picosecond,nanosecond and continuous wave lasers have been investigated with different feed speeds tested to study the machining efficiency.The cutting temperature,and geometrical outputs have been measured to investigate the thermal influence on the cooling behaviour of the bone samples while high-speed imaging was used to compare the material removal mechanisms between a pulsed and continuous wave laser.Furthermore,an in-depth histological analysis of the subsurface has revealed that the nanosecond laser caused the largest necrotic depth,owing to the high pulse frequency limiting the dissipation of heat.It has also been observed that surface cracks positioned perpendicular to the trench direction were produced after machining by the picosecond laser,indicative of the photomechanical effect induced by plasma explosions.Therefore,the choice of laser type(i.e.,in terms of its pulse width and frequency)needs to be critically considered for appropriate application during laser osteotomy with minimum damage and improved healing.

Bulk and surface damages in complementary bipolar junction transistors produced by high dose irradiation

Two complementary types NPN and PNP of bipolar junction transistors(BJTs) were exposed to high dose of neutrons and gamma rays. The change in the base and collector currents, minority carriers lifetime, and current gain factor β with respect to the dose were analyzed. The contributions of the base current according to the defect types were also reported.It was declared that the radiation effect of neutrons was almost similar between the two transistor types, this effect at high dose may decrease the value of β to less than one. The Messenger-Spratt equation was used to describe the experimental results in this case. However, the experimental data demonstrated that the effect of gamma rays was generally higher on NPN than PNP transistors. This is mainly attributed to the difference in the behavior of the trapped positive charges in the SiO_2 layers. Meanwhile, this difference tends to be small for high gamma dose.

Characterization of surface damage of a solid plate under tensile loading using nonlinear Rayleigh waves

This letter reports experimental observation of a direct correlation between the acoustic nonlinearity parameter (NP) measured with nonlinear Rayleigh waves and the accumulation of plasticity damage in an AZ31 magnesium alloy plate specimen.Rayleigh waves are generated and detected with wedge transducers,and the NPs are measured at different stress levels.The results show that there is a significant increase in the NPs with monotonic tensile loads surpassing the material's yielding stress.The research suggests an effective nondestructive evaluation method to track the surface damage in metals.

INVESTIGATION OF SURFACE DAMAGE OF LiNbO_3 IMPLANTED BY Ti ION

In this paper, damages and annealing effects of X,Y and Z cut LiNbO-3 implanted by 350keV high energy Ti (1.5 x 1017 / cm2) are studied. The surface damages of X,Y cut plates are nearly amorphous, but the surface damage of Z cut does not reach saturation. Radiation damage is mainly due to Nb moving atoms and Ti atoms occupy the interstitial sites. By annealing the sample at 1000℃, most damage is removed from the boundary between implanted layer and LiNbO3 base to surface.

A review of surface damage/microstructures and their effects on hydrogen/helium retention in tungsten

The change in surface damage/microstructures and its effects on the hydrogen(H)isotope/helium(He)dynamic behavior are the key factors for investigating issues of tungsten(W)-based plasma-facing materials(PFMs)in fusion such as surface erosion,H/He retention and tritium(T)inventory.Complex surface damage/microstructures are introduced in W by high-temperature plasma irradiation and new material design,typically including pre-damage and multi-ion co-deposition induced structures,solute elements and related composites,native defects like dislocations and interfaces,and nanostructures.Systematic experimental and theoretical researches were performed on H isotope/He retention in complex W-based materials in the past decades.In this review,we aim to provide an overview of typical surface damage/microstructures and their effects on H/He retention in W,both in the experiment and multiscale modeling.The distribution/state,dynamics evolution,and interaction with defects/microstructures of H/He are generally summarized at different scales.Finally,the current difficulties,challenges and future directions are also discussed about H/He retention in complex W-based PFMs.

Rail RCF damage quantification and comparison for different damage models

There are several fatigue-based approaches that estimate the evolution of rolling contact fatigue(RCF) on rails over time and built to be used in tandem with multibody simulations of vehicle dynamics. However, most of the models are not directly comparable with each other since they are based on different physical models even though they shall predict the same RCF damage at the end.This article studies different approaches to quantifying RCF and puts forward a measure for the degree of agreement between them. The methodological framework studies various steps in the RCF quantification procedure within the context of one another, identifies the ‘primary quantification step’ in each approach and compares results of the fatigue analyses. In addition to this, two quantities—‘similarity’ and ‘correlation’—have been put forward to give an indication of mutual agreement between models.Four widely used surface-based and sub-surface-based fatigue quantification approaches with varying complexities have been studied. Different operational cases corresponding to a metro vehicle operation in Austria have been considered for this study. Results showed that the best possible quantity to compare is the normalized damage increment per loading cycle coming from different approaches. Amongst the methods studied, approaches that included the load distribution step on the contact patch showed higher similarity and correlation in their results.While the different approaches might qualitatively agree on whether contact cases are ‘damaging’ due to RCF, they might not quantitatively correlate with the trends observed for damage increment values.

Fatigue Life Analysis of Coiled Tubing in Deep Well Jet Plugging Removal

The coiled tubing plugging has become the main means of plugging in gas Wells in Xinjiang. These Wells are deep and have high pressure, which can easily affect the fatigue life of the operating coiled tubing. In order to improve the life of coiled tubing in high-pressure gas Wells, this paper studies the plugging conditions of coiled tubing in high-pressure ultra-deep Wells. Firstly, the cross section deformation of coiled tubing under high internal pressure is analyzed. Secondly, the factors influencing the fatigue life of coiled tubing and the influence of surface damage on the fatigue life of coiled tubing were studied. Finally, the mechanism of furrow damage caused by coiled tubing and the main measures to reduce furrow damage are analyzed. The following suggestions are made to improve the life of coiled tubing: select the right material and the right size coiled tubing;Use appropriate measures to prevent premature coiled tubing failure and reduce operating costs.

Towards a unified classification of wear

Since the beginning of the systematic study of wear,many classification schemes have been devised.However,though covering the whole field in sum,they stay only loosely connected to each other and do not build a complete general picture.To this end,here we try to combine and integrate existing approaches into a general simple scheme unifying known wear types into a consistent system.The suggested scheme is based on three classifying criterions answering the questions“why”,“how”and“where”and defining a 3-D space filled with the known wear types.The system can be used in teaching to introduce students to such complex phenomena as wear and also in engineering practice to guide wear mitigation initiatives.

Examination on the wear process of polyformaldehyde gears under dry and lubricated conditions

This study presents the results of detailed wear process examination on polyformaldehyde gears under both dry and lubricated conditions.A multi-purpose durability test rig was employed to study the wear performance of polyformaldehyde gear pairs.The wear behaviors of polyformaldehyde gears under dry and oil-lubricated operating conditions were characterized via measurements of gear tooth surface micro-topography and tooth profile deviation.Under the dry running condition,a hump and a gully appear on the tooth surface in the pitch line area of the driving gear and the driven wheel,respectively.The largest amount of wear was observed around the tooth root of the driving gear.However,the gear tooth wear pattern with lubrication is different from that under the dry running condition.

Mechanical Analysis and Strength Checking of Current Collector Failure in the Winding Process of Lithium-Ion Batteries

The current collector fracture failure of lithium-ion batteries(LIBs)occurs during its winding production process frequently,and the consequent damages are usually large,but little research has been conducted on this phenomenon.This work stems from the difficulty and obstacles in the winding process of actual production of LIBs.The fracture failure of the current collectors is easily caused by the evolution and mutation of the mechanical behavior during the winding process,resulting in safety hazards and poor efficiency.The purpose of this work is to reveal the evolution and distribution mechanism of circumferential strain of the current collectors on the fracture failure under the constraint of winding process.Experimental tests,finite element calculations and theoretical model are used to study the evolution and distribution of circumferential strain.The dynamic evolution process of circumferential strain is tested accurately,and the mechanism of fracture failure of current collectors is revealed.The criterion for current collector strength is proposed based on the results of strain analysis and SEM observation.