• Modelling of the dynamic tool-chip interface in metal cutting

      Qi, Hong Sheng; Mills, B. (2003)
      The formation of tribo-layers during machining is very common phenomena, especially when machining `free machining¿ steels. Several kinds of tribo-layers formed in metal cutting processes have been reported, layers of inclusions from the workpiece, oxide layers due to chemical reaction, plastic deformation layers, material transfer layers (MTLs) or built-up layers (BULs). A new tool¿chip contact model is proposed to explain the tribo-layer phenomena, which considers the nature of the shear strain rate distribution in the secondary deformation zone. A shear strain rate distribution in this zone having a shape similar to that found in the preliminary zone is proposed. A cutting interface (CI) is defined and this interface is at different location to the material boundary of tool and chip (MBTC). This difference is a key factor in the formation of the tribo-layer in the secondary deformation zone. This model can be used in improving tool wear prediction and the estimation of tool life.
    • A new paradigm for disc-pad interface models in friction brake system

      Qiu, L.; Qi, Hong Sheng; Wood, Alastair S. (2015)
      In this paper a 2D coupled thermal-stress finite element model is established and used to predict thermal phenomena at the disc-pad interface of a disc brake system. The importance of certain critical settings and parameters for the 2D FE model has been identified (such as, a limited degree of freedom for a brake pad in place of accepted practice that considers uniform contact), here a non-uniform pressure distribution resulting from friction bending moment effects due to the introduction of a pivot point. These parameters affect the distributions of both interface temperature and pressure. The simulation results show that when the interface conductance h is 10^6 W/m^2K or higher, the interface temperature distribution is no longer sensitive to friction bending moment effects. However, when h is 30000 W/m^2K or lower, the interface temperature distribution and heat partition ratio are significantly affected by the setting used for the rotational degree of freedom of the pad. The simulation results provide a useful reference for a better design of a disc brake system for different applications.
    • A numerical and experimental study on the factors that influence heat partitioning in disc brakes

      Loizou, Andreas; Qi, Hong Sheng; Day, Andrew J. (Scientific Society of Mechanical Engineering (GTE), 2010-06)
      To investigate the heat partition on a vehicle disc brake, a small scale test rig with one contact interface was used. This allowed the disc/pad contact temperatures to be measured with fast-response foil thermocouples and a rubbing thermocouple. Based on the experimental conditions a 3D symmetric disc brake FE model has been created. Frictional heat generation was modelled using the ABAQUS finite element analysis software. The interface tribo-layer which affects heat partitioning was modelled using an equivalent thermal conductance value obtained from the authors¿ previous work. A 10 second drag braking was simulated and the history and distribution of temperature, heat flux multiplied by the nodal contact area, heat flux leaving the surface and contact pressure was recorded. Test rig and FE model temperatures were compared to evaluate the two methods. Results show that heat partitioning varies in space and time, and at the same time contact interface temperatures do not match. It is affected by the instantaneous contact pressure distribution, which tends to be higher on the pad leading edge at the inner radius side. They are also affected by the thermal contact resistance at the components contact interface.
    • Numerical Investigation of Conjugate Natural Convection Heat Transfer from Discrete Heat Sources in Rectangular Enclosure

      Gdhaidh, Farouq A.S.; Hussain, Khalid; Qi, Hong Sheng (2014)
      The coupling between natural convection and conduction within rectangular enclosure was investigated numerically. Three separate heat sources flush mounted on a vertical wall and an isoflux condition was applied at the back of heat sources. Continuity, momentum and energy conservation equations were solved by using control volume formulation and the coupling of velocity and pressure was treated by using the “SIMPLE” algorithm. The modified Rayleigh number and the substrate/fluid thermal conductivity ratio were used in the range 𝑹𝒂𝒍𝒛∗=𝟏𝟎^𝟒−𝟏𝟎^𝟕 and 𝑹𝒔=𝟏𝟎−𝟏𝟎𝟎𝟎 respectively. The investigation was extended to compare results of FC-77 with Air and also for high values of 𝑹𝒔>𝟏𝟎𝟎𝟎. The results illustrated that, when the modified Rayleigh number increases, dimensionless heat flux and local Nusselt number increases for both fluids. Opposite behaviour for the thermal spreading in the substrate and the dimensionless temperature 𝜽, they were decreased when 𝑹𝒂𝒍𝒛∗ is increased. Also with increasing the substrate/fluid thermal conductivity ratio for a given value of the modified Rayleigh number the thermal spreading in the substrate increased which is the reason of the decrease in the maximum temperature value. The present study concluded that, for high values of 𝑹𝒔>𝟏𝟓𝟎𝟎, the effect of the substrate is negligible.
    • A numerical investigation of hot spotting origin of ventilated disc brakes

      Tang, Jinghan; Bryant, David; Qi, Hong Sheng (2015)
      Hot spots are high thermal gradients on the disc surface during brake events which can cause the undesired phenomena of thermal judder and drone. The origin of hot spotting has been presented by various theories such as Thermo elastic instability (TEI) and progressive waviness distortions (PWD). However, majority of the numerical models based on these theories mainly concentrated on solid disc rather than ventilated disc which is the most commonly used nowadays. According to the experimental work done by the authors, disc geometry factors such as vents and pins also have correlations with hot spot distribution; these phenomena are difficult to be predicted analytically. Thus a convenient 2D asymmetric finite element simulation has been performed in order to obtain the correlations observed in experiments. Further parameter studies investigated factors such as uneven initial temperature, vents, pins and pad length. The results have been correlated with the experimental data and demonstrate the contribution of geometric factors in the generation of hot spots and hot judder.
    • Numerical Study of Conjugate Natural Convection from Discrete Heat Sources.

      Gdhaidh, Farouq A.S.; Hussain, Khalid; Qi, Hong Sheng (2015)
      The coupling between natural convection and conduction within rectangular enclosure was investigated numerically. Three separate heat sources were flush mounted on a vertical wall and an isoflux condition was applied at the back of heat sources. The governing equations were solved using control volume formulation. A modified Rayleigh number and a substrate/fluid thermal conductivity ratio were used in the range 10^4 −10^7 and 10−10^3 respectively. The investigation was extended to examine high thermal conductivity ratio values. The results illustrated that, when Rayleigh number increased the dimensionless heat flux and local Nusselt number increased and the boundary layers along hot, cold and horizontal walls were reduced significantly. An opposite behaviour for the thermal spreading in the substrate and the dimensionless temperature, were decreased for higher Rayleigh number. Moreover, the thermal spreading in the substrate increased for higher substrate conductivity, which affected the temperature level. However the effect of the substrate is negligible when the thermal conductivity ratio higher than 1,500.
    • Numerical Study of Conjugate Natural Convection Heat Transfer Using One Phase Liquid Cooling

      Gdhaidh, Farouq A.S.; Hussain, Khalid; Qi, Hong Sheng (2014)
      A numerical study in 3-D is performed using water as a cooling fluid to investigate the one phase natural convection heat transfer within enclosure. A heat source representing a computer CPU mounted on one vertical wall of a rectangular enclosure is simulated while a heat sink is installed on the opposite vertical wall of the enclosure. The air flow inside the computer compartment is created by using an exhaust fan, and the flow is assumed to be turbulent. The applied power considered ranges from 15 40 W. In order to determine the thermal behaviour of the cooling system, the effect of the heat input and the dimension of the enclosure are investigated. The results illustrate that as the size of the enclosure increase the chip temperature declined. However the drop in the temperature is very small when the width increased more than 50 mm. When the enclosure was filled with water the temperature was reduced by 38%. Also the cooling system maintains the maximum chip temperature at 71.5 C when the heat input of 40 W was assumed and this is within the current recommended computer electronic chips temperature of no more than 85 degrees C.
    • Simplified three-dimensional finite element hot-spotting modelling of a pin-mounted vented brake disc: an investigation of hot-spotting determinants

      Tang, Jinghan; Bryant, David; Qi, Hong Sheng; Whiteside, Benjamin R.; Babenko, Maksims (2018-06)
      Hot spotting is a thermal localisation phenomenon in which multiple hot regions form on a brake disc surface during high energy and/or high speed braking events. As an undesired problem, hot spots can result in high order brake judder, audible drone and thermal cracking. This paper presents a finite element model for hot spot modelling which introduces the classical axisymmetric assumptions to the brake pad in 3D by scaling the material properties combined with a subroutine to simulate the heat generation instead of modelling the rotation of the brake pad. The results from the initial feasibility models showed significant improvement in computing efficiency with acceptable accuracy when compared to a traditional FE model without such simplifications. This method was then applied to the 3D simulation of hot spotting on a realistic ventilated brake disc/pad pair and the results showed good correlation with experiments. In order to improve the understanding of the hot spotting mechanism, parametric studies were performed including the effects of solid and ventilated disc geometry, rotational speed and energy, pins, disc run-out, and brake pad length. Based on the analysis of the results, it was identified that the vents and pins affected the hot spot distribution. Speed was shown to be more important on the hot spot generation time and distribution than either the pressure or total energy input. Brake disc run-out was shown to affect the magnitude of both hot spot temperature and height due to the non-linear relationship between local deformation, contact pressure and heat generation. Finally, increasing the brake pad length generated fewer hot spots but the temperature of each hot spot increased.
    • Simulation Model of Maritime Inventory Routing Problem with Particular Application to Cement Distribution

      Wirdianto, E.; Qi, Hong Sheng; Khan, M. Khurshid (2011)
      Simulation is undoubtedly a very useful tool for modelling a system specifically in the presence of stochastic elements and complex interactions between the system entities. In this paper, a simulation model to support decision making in ship scheduling for Maritime Inventory Routing Problem (MIRP) with particular application to cement distribution is presented. The system under study is a combined discrete and continuous system, where a heterogeneous fleet of ships with various sizes and types of contracts transport bulk cement products from production facility (Central Supply, CS) of a cement company to its packing plants (Distribution Centres, DCs). The simulation model in this study has been designed and developed thoroughly to emulate the complexity of the real system of the MIRP. The simulation model has demonstrated the capability to provide support for decision making in ship scheduling of the heterogeneous shipping fleet in the following forms: (a) real time states of inventory levels at CS and DCs and (b) ships’ routing. In addition, one of the main strength of this simulation model is its flexibility. It can be easily expanded or adjusted to different size of system entities for example number of CSs, DCs, berths, vessels, and products.
    • Systematic Digitized Treatment of Engineering Line-Diagrams

      Sui, T.Z.; Qi, Hong Sheng; Qi, Q.; Wang, L.; Sun, J.W. (2015-05)
      In engineering design, there are many functional relationships which are difficult to express into a simple and exact mathematical formula. Instead they are documented within a form of line graphs (or plot charts or curve diagrams) in engineering handbooks or text books. Because the information in such a form cannot be used directly in the modern computer aided design (CAD) process, it is necessary to find a way to numerically represent the information. In this paper, a data processing system for numerical representation of line graphs in mechanical design is developed, which incorporates the process cycle from the initial data acquisition to the final output of required information. As well as containing the capability for curve fitting through Cubic spline and Neural network techniques, the system also adapts a novel methodology for use in this application: Grey Models. Grey theory have been used in various applications, normally involved with time-series data, and have the characteristic of being able to handle sparse data sets and data forecasting. Two case studies were then utilized to investigate the feasibility of Grey models for curve fitting. Furthermore, comparisons with the other two established techniques show that the accuracy was better than the Cubic spline function method, but slightly less accurate than the Neural network method. These results are highly encouraging and future work to fully investigate the capability of Grey theory, as well as exploiting its sparse data handling capabilities is recommended.
    • Two-dimensional finite element analysis investigation of the heat partition ratio of a friction brake

      Qiu, L.; Qi, Hong Sheng; Wood, Alastair S. (2018-12)
      A 2D coupled temperature-displacement FE model is developed for a pad-disc brake system based on a restricted rotational pad boundary condition. The evolution of pressure, heat flux, and temperature along the contact interface during braking applications is analysed with the FE model. Results indicate that different rotational pad boundary conditions significantly impact the interface pressure distribution, which in turn affects interface temperature and heat flux distributions, and suggest that a particular pad rotation condition is most appropriate for accurately modelling friction braking processes. The importance of the thermal contact conductance in the analysis of heat transfer in friction braking is established, and it is confirmed that the heat partition ratio is not uniformly distributed along the interface under normal and high interface thermal conductance conditions.