Cooling and Crack Suppression of Bone Material Drilling Based on Microtextured Bit Modeled on Dung Beetle

In recent years, the number of patients with orthopedic diseases such as cervical spondylosis has increased, resulting in an increase in the demand for orthopedic surgery. However, thermal necrosis and bone cracks caused by surgery severely restrict the development and progression of orthopedic surgery. For the material of cutting tool processing bone in bone surgery of drilling high temperature lead to cell death, easy to produce the problem such as crack cause secondary damage effects to restore, in this paper, a bionic drill was designed based on the micro-structure of the dung beetle’s head and back. The microstructure configuration parameters were optimized by numerical analysis, and making use of the optical fiber laser marking machine preparation of bionic bit; through drilling test, the mathematical model of drilling temperature and crack generation based on micro-structure characteristic parameters was established by infrared thermal imaging technology and acoustic emission signal technology, and the cooling mechanism and crack suppression strategy were studied. The experimental results show that when the speed is 60 m/min, the cooling effects of the bionic bit T1 and T2 are 15.31% and 19.78%, respectively, and both kinds of bits show obvious crack suppression effect. The research in this paper provides a new idea for precision and efficient machining of bone materials, and the research results will help to improve the design and manufacturing technology and theoretical research level in the field of bone drilling tools

Heat transfer correlation for flow boiling in small to micro tubes

This article is available open access under a Creative Commons license (http://creativecommons.org/licenses/by-nc-nd/3.0/) Copyright © 2013 The Authors. Published by Elsevier Ltd. All rights reserved.There is a large discrepancy in the open literature about the comparative performance of the existing macro and microscale heat transfer models and correlations when applied to small/micro flow boiling systems. This paper presents a detailed comparison of the flow boiling heat transfer coefficient for R134a in stainless steel micro tubes with 21 macro and microscale correlations and models. The experimental database that was used in the comparison includes the data for 1.1 and 0.52 mm diameter tubes, mass flux range of 100–500 kg/m2 s and system pressure range 6–10 bar obtained in the course of this study. The effect of the evaporator heated length on the comparative performance of the correlations and models was investigated using three different lengths of the 1.1 mm diameter tube (L = 150, 300 and 450 mm). This comparative study demonstrated that none of the assessed models and correlations could predict the experimental data with a reasonable accuracy. Also, the predictability of most correlations becomes worse as the heated length increases. This may contribute in explaining the discrepancy in the comparative performance of the correlations from one study to another. A new correlation is proposed in the present study based on the superposition model of Chen. The database used in developing the correlation consists of 5152 data points including the current experimental data and data obtained previously with the same test rig, fluid and methodology for tubes of diameter 4.26, 2.88, 2.01 mm. The new correlation predicted 92% of the data within the ±30% error bands with a MAE value of 14.3%

Fatigue crack propagation in Al-Li alloy 8090 : environmental effects

Fatigue crack propagation behaviour in Al-Li alloy 8090 plate were studied in four main testing environments: a relatively inert environment - desiccated air; and three freely corroding aqueous environments consisting of distilled water, 0.6 M NaCl and 1 M AlCl₃. It was found that the major role of the aqueous environments in the T-L orientation crack growth behaviour of the Al-Li alloy plate was to promote S-L splitting (delamination) at grain boundaries, with a subsequent effect on the stress state at the crack tip. The splitting preceded the main crack advance, and helped to keep the crack in the same macroscopic crack plane and restricted the fracture surface roughness, and consequently reduced crack closure effects. In contrast, the absence of the splitting effects in desiccated air, combined with the planar deformation features and the strong crystallographic texture of the Al-Li alloy plate, led to out-of-plane cracking and ridge formation in the mid-thickness of the specimen. This resulted in severe crack growth retardation and a crack growth rate plateau at ΔK values above ∼ 3 MPa.m[sub ½]. Analyses of the observations led to the conclusion that the S-L splitting phenomenon is associated with both localized anodic dissolution processes and hydrogen embrittlement effects. The effect of changing the loading frequency was not obvious, except in the dry air environment where decreasing the frequency from ∼80 to ∼0.5 Hz led to the disappearance of the crack growth rate plateau. The fatigue cracking resistance of the Al-Li alloy plate is superior in the dry air environment and slightly better or equivalent in the aqueous environments when compared to a conventional crack-tolerant Al-alloy plate, 2024-T35 1. The effects of a re-aging treatment on fatigue cracking in the S-L orientation of the Al-Li plate were also studied. The presence of aqueous environments also accelerated crack propagation in the S-L orientation, and crack propagation is faster in the S-L orientation than in the T-L orientation. The re-aging treatment was effective in increasing the short-transverse fracture toughness and also improved the intergranular corrosion resistance of the material. However, the re-aging treatment did not improve the corrosion fatigue crack propagation resistance.Applied Science, Faculty ofMaterials Engineering, Department ofGraduat