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In this paper, the tool wear mechanism in low-frequency vibration-assisted drilling (LF-VAD) of carbon fiber reinforced polymer (CFRP)/Ti6Al4V stacks has been proposed using variably machining parameters. Based on the kinematics analysis, the effect of vibration amplitude on the chip formation, uncut chip thickness, chip radian, and axial velocity was presented. Subsequently, the effect of LF-VAD on the cutting temperature, tool wear, delamination, and geometrical accuracy was presented for different vibration amplitude. The LF-VAD with the utilization of minimum quantity lubricant (MQL) resulted in a successful drilling process of 50 holes, with a 63 % reduction of the cutting temperature. For the rake face, LF-VAD reduced the adhered height of Ti6Al4V by 80 % at low cutting speed and reduced the crater depth by 33 % at the high cutting speed. On the other hand, LF-VAD reduced the flank wear land by 53 %. Furthermore, LF-VAD showed a significant enhancement on the CFRP delamination, geometrical accuracy, and burr formation.

The use of lightweight material such as CFRP/Ti6Al4V in stacked structures in the aerospace industry is associated with improved physical and mechanical characteristics. The drilling process of nonuniform structures plays a significant role prior to the assembly operation. However, this drilling process is typically associated with unacceptable CFRP delamination, hole accuracy, and high tool wear. These machining difficulties are attributed to high thermal load and poor chip evacuation mechanism. Low-frequency vibration-assisted drilling (LF-VAD) is an advanced manufacturing technique where the dynamic change of the uncut chip thickness is used to manipulate the cutting energy. An efficient chip evacuation mechanism was achieved through axial tool oscillation. This study investigates the effect of vibration-assisted drilling machining parameters on tool wear mechanisms. The paper also presents the effect of tool wear progression on drilled hole quality. Hole quality is described by CFRP entry and exit delamination and hole accuracy. The results showed a significant reduction in the thrust force, cutting torque, cutting temperature, and flank wear-land.

Recent trends aim at efficient and sustainable cooling strategies for machining hard-to-cut materials. This research is concerned with combining cryogenic cooling and minimum quantity lubrication to benefit from their respective cooling and lubrication capabilities. Fundamental understanding of the flow characteristics of the two jets, their interaction, and relative position was carried out using experimentally validated CFD and FE modelling of the cutting zone. The performance of the optimized hybrid system was evaluated experimentally and compared to flood, high pressure and cryogenic cooling in machining of Ti-alloys. Results showed an improvement in tool life when using the optimized hybrid cooling technique.

Carbon fiber-reinforced polymers (CFRP) are widely used in the aerospace industry. A new generation of aircraft is being built using CFRP for up to 50% of their total weight, to achieve higher performance. Exit delamination and surface integrity are significant challenges reported during conventional drilling. Exit delamination influences the mechanical properties of machined parts and, consequently, reduces fatigue life. Vibration-assisted drilling (VAD) has much potential to overcome these challenges. This study is aimed at investigating exit delamination and geometrical accuracy during VAD at both low- and high-frequency ranges. The kinematics of VAD are used to investigate the relationship between the input parameters (cutting speed, feed, vibration frequency, and amplitude) and the uncut chip thickness. Exit delamination and geometrical accuracy are then evaluated in terms of mechanical and thermal load. The results show a 31% reduction in cutting temperature, as well as a significant enhancement in exit delamination, by using the VAD technology.

The heat transfer from rotating workpieces in dry and laser-assisted machining turning operations has significant effect on the part temperature field and consequently the cutting forces, microstru...

Fretting fatigue and wear problems have major economical and safety impact on the nuclear industry. This keynote paper provides examples of the fretting problems encountered in nuclear power stations and an overview of the methodologies used to assess their root cause, their potential effect on the integrity of structural components and the future damage projection for risk management. The limitations of existing models that are commonly used to predict fretting wear rate are discussed. A system approach to the fretting wear/fatigue problem allowed us to significantly improve the capability of predicting fretting damage through the recognition of the problem nonlinearity, and the effect of self-induced changes. The application of linear elastic fracture mechanics principles for predicting the fretting wear and fretting fatigue strength is demonstrated. The paper underlines the critical roles of the following two factors. First, the validation of the above mentioned methodologies, through experimental investigation of the long-term fretting wear and fatigue behavior of structural components under realistic operating conditions. Second, the qualification of in -situ measurements of fretting wear damage using nondestructive evaluation NDE and inspection methods.

Zirconium alloys are highly desirable in nuclear applications due to their transparency to thermal energy neutrons and for their high corrosion resistance. The main objective of this study is to investigate the fretting wear mechanism of Zr–2.5%Nb alloy. The experimental work was carried out in air at 265 °C, using a specially designed fretting wear tribometer. The transfer of material, the change in the wear volume and the maximum wear depth with the number of cycles were measured through 3D mapping of the topography of the fretted surface. SEM and Fourier Transform Infrared Interferometry methods were used to examine the microspall pits and to measure the distribution of the thickness of oxide layer in the fretting region. For relatively small slip amplitude, the results showed that the fretting wear mechanism is initially dominated by adhesion and abrasion actions and then by delamination and surface fatigue. The time variation of the wear losses was shown to be cyclic until a steady state value is reached. At high slip amplitudes, however, abrasion and delamination are the only dominant wear mechanisms. The volumetric wear losses were found to decrease monotonically with the number of cycles. A novel approach was introduced, whereby the thermal and electrical contact resistances of the fretting interface are simultaneously measured. The results demonstrated the potential use of this non-intrusive approach for real-time monitoring of the fretting wear mechanism.

Proper design and reliable operation of nuclear power generating plants require accurate prediction of fretting wear failure criteria, which include the volumetric wear losses, the maximum wear depth and minimum root radius of the scar. A unique three-axis fretting wear test facility was developed to simulate the in-plane and out-of-plane dynamic characteristics of the bearing pad/pressure tube tribo-system. The fretting wear of Zr–2.5% Nb alloy at 265 °C was investigated. The results showed that the specific wear rate coefficient decreases with the increase of work rate, and is not constant as it is commonly assumed. The increase in the maximum wear depth with the accumulated wear energy was shown to be approximated by a second-order polynomial function. The correlation between the maximum wear depth hmax and the minimum root radius Rr, has been established, an aspect that has never been investigated before. Examination of the fret scars showed that they can be classified into three types. When the ratio hmax/ R r was correlated to hmax, the data are contained within a well-defined bell-shaped envelope, which resembles the normal distribution curve.

A fracture mechanics model has been developed to estimate the fretting fatigue strength and the service life of structural components. Integrated in this model is a contact problem solver that is automated to deal with the geometric and material nonlinearities of the problem. A three-dimensional interface element was developed to model the constitutive laws of the interface. The results demonstrated the capability of the model to predict the conditions under which small fretting-induced fatigue cracks are arrested. The model was validated by predicting the S-N curves produced experimentally for Inconel 600 at high temperature. The prediction of the fretting fatigue limit was found to be in excellent agreement with the experimental results.