Analysis Of Residual Strain And Stress Distributions In High Speed Milled Specimens Using An Indentation Method (original) (raw)
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Evaluation of Residual Stresses Induced by High Speed Milling Using an Indentation Method
Modern Mechanical Engineering, 2012
In this work, a recently developed method based on the change of distance between collinear indents is used to evaluate different states of residual stress, which were generated in samples of AA 6082-T6 and AA 7075-T6 aluminium alloys milled at high speed. One of the advantages of this method, which needs a universal measuring machine, is not requiring neither the use of specific equipment nor highly skilled operators. Also, by integrating an indentation device to the mentioned machine, the absolute error of measurement can be reduced. In results obtained in samples subjected to different cutting conditions it is observed a correlation between the stress values and the depth of cut, showing the AA 6082-T6 alloy higher susceptibility to be stressed. Furthermore, the high sensitivity of the method allowed detecting very small differences in the values reached by different normal components in the zones corresponding to climb and conventional cutting. It is important to note that these differences were similar for both evaluated alloys. Finally, the directions associated with the principal components of residual stress, where maximum local plastic stretching occurs, were found to be strongly dependent on the rolling direction prior to machining.
Experimental Mechanics, 2009
An improved method of indent pairs is utilised to determine residual stresses in high speed milling specimens of AA 6082-T6 and AA 7075-T6 aluminium alloys. To carry out the measurement procedure, this approach does not need specific equipment but only requires a universal measuring machine and an oven. An indentation device is incorporated to the measuring machine, which allows reducing the absolute error of measurement to just ±0.9 MPa. The geometry of the tool and cutting parameters are selected to evaluate the sensitivity of the method. The residual stress distributions generated by high speed milling are exhaustively evaluated taking into account orthogonal components of cutting speed and tangential force, which are parallel and perpendicular to feed direction.
Study of Residual Stresses from Two Machining Protocols Using an Indentation Method
International Journal of Mechanical Engineering and Applications, 2013
Although high-speed machining offers a number of advantages over conventional machining, it is possible that the residual stress distributions generated by the former can affect the service life of the processed components. In this paper, a newly developed micro-indent method is used to evaluate different residual stress states, which were introduced in samples of AA 7075-T6 aluminum alloy milled at low and high-speed. Different surfaces were generated by varying the cutting speed in one order of magnitude, from 100 m/min to 1000 m/min. Two machining protocols, which consist of using different machine tools, were evaluated. The results show that it is possible to generate and to evaluate very small residual stresses. Finally, the values and levels obtained for normal components were analyzed in function of mechanical and thermal effects that generated the residual stresses.
Journal of Materials Processing Technology, 2015
Deformation machining is a combination of thin structure machining and single point incremental forming/bending. It enables the creation of monolithic structures with complex geometries in one setup, employing conventional manufacturing techniques. Previously, such components would either be assembled or manufactured using complex dies and machinery. Residual stresses generated during the machining and forming has direct implications on the product life cycle and properties. It is essential to understand the process effects on the residual stress distribution. In the present work, an experimental study of surface residual stress for deformation machining (bending and stretching mode) has been performed. The nano indentation technique has been employed to examine the residual stresses. The experimental results have shown the generation of compressive surface residual stresses during machining and tensile surface residual stresses during forming (bending and stretching) operations. Significant variation in the surface residual stresses with varying machining and forming parameters has been observed.
European Journal of Mechanics A-solids, 2011
The local mechanical properties of a weld zone, in a 6061-T6 aluminium alloy subjected to the modified indirect electric arc technique have been studied. The mechanical properties of the base metal, the weld metal and the heat affected zone were determined by means of usual and instrumented indentation testing, as well as micro-traction testing. To analyse the heat input effect resulting from the welding process, the evolution of the weld zone size was evaluated by means of classical indentation under a constant applied load. The results were presented using a Vickers hardness map representation. This allows monitoring exact hardness variation while leading to the identification of the different zones of the welded joint. Instrumented indentation testing was carried out to determine the local mechanical properties, such as the yield stress, the bulk modulus and the strain-hardening exponent. Obtained results are compared to those derived from tensile tests conducted on micro-specimen cuts taken from the weld zone. It was observed that yield stress values are directly comparable for indentation and micro-traction experiments. As for the elastic properties, no comparison was possible since the bulk modulus is measured by indentation, whereas it is the Young's modulus by tensile test. The microtraction testing seems to be more sensitive to represent the work hardening of a material since the corresponding exponent is found to be constant by instrumented indentation.
Monolithic aluminium alloy parts are highly required in aeronautical industry, but they show significant geometrical distortion after the machining process. This work investigated the distortion attributed by the initial residual stress of raw material and the machining induced residual stress during the milling process, as well as explored the effects of the machining toolpath strategy. Single-/multi-pocket parts were milled from 7050-T7451 aluminium blocks with different initial residual stress, and an element deletion method was developed for numerical study to simulate different sequences of material removal. It was revealed that the toolpath parallel to the long side of block caused more distortion on the side surfaces of final part. The value of distortion was positively correlated to the magnitude of initial residual stress of raw material. The simulation results indicated that the distortion attributed by machining induced residual stress accounted for about 15% of final dis...
Indentation Size Effect of Heat Treated Aluminum Alloy
Acta Metallurgica Slovaca, 2019
The aim of the submitted work is to study the influence of applied loads ranging from 0.09807 N to 0.9807 N on measured values of micro-hardness of heat treated aluminum alloy 6082. The influence of applied load on a measured value of micro-hardness was evaluated by Meyer’s index n, PSR method and by Analysis of Variance (ANOVA). The influence of the load on the measured value of micro-hardness is statistically significant and the relationship between the applied load and micro-hardness manifests the moderate reverse ISE. As the temperature of the solution treatment rises, the YS/UTS ratio and also Meyer’s index n, measured and “true hardness“ increase. On the other hand, its effect on the plastic properties of the alloy is ambiguous.
International Journal of Materials, Mechanics and Manufacturing, 2015
The aim of this research was to investigate the residual stresses in an aluminum alloy Al-6061 workpiece after machining. The sensitivity of residual stresses to cutting speed and feed rate was determined using finite element method. Tensile residual stresses at the surface of components are generally undesirable as they contribute to fatigue failure, quench cracking and stress-corrosion cracking. A two dimensional model of machining was developed using commercially available finite element software, Abaqus, to simulate orthogonal cutting of Al-6061 alloy. Numerical simulations of orthogonal cutting of the workpiece were carried out at various preselected combinations of feed rate and cutting speed. The simulation results showed that residual stresses were insensitive to changes in cutting speed, however, residual stresses were clearly affected by the change in feed rate.
Computational Materials Science, 2010
Aluminium alloys for the aerospace industry are often clad by roll-bonded aluminium to improve corrosion resistance. The clad layer is of the order of 100 lm in thickness and it is difficult to determine the mechanical properties of this layer by conventional mechanical testing techniques. Nanoindentation is ideally suited to determining the elastic and plastic properties of such layers and here we report on a combined approach using experimental nanoindentation and finite element analysis to extract yield stress and strain hardening exponent for an Al-clad system. The approach used was calibrated against results for an Al 2024-T351 alloy, where conventional mechanical testing data was available. For the Al 2024-T351, a forward analysis was used for extraction of load-displacement curves at different indentation depths with the help of elastic-plastic properties obtained from tensile testing. For a $100 lm clad layer of pure aluminium on Al 2024-T351, reverse analysis was used for extraction of elastic-plastic properties from a single indentation test. A yield stress of 110-120 MPa and a value of 0.075-0.1 for the work hardening exponent was obtained for the Al cladding. Nanoindentation properties including maximum load of indentation, contact depth, area of contact and pile-up obtained from the forward and reverse analyses showed excellent agreement with the experimental results.