Michael R. Lovell

Predicting springback in sheet metal forming: an explicit to implicit sequential solution procedure

The springback properties of sheet metals make the design of forming dies extremely difficult. In this work a coupled explicit to implicit finite element procedure is outlined for predicting springback deformations in sheet metal forming processes. The explicit method is initially utilized to analyze the contact based forming operation of a production stamping process. Then, an implicit solution is performed to simulate the springback that develops in a blank after the forming pressure has been removed. Using this simultaneous solution technique on an actual automotive component, numerically predicted springback deformations are found to be within 1% of production values. The results of the numerical investigation indicate that the coupled finite element procedure described herein can be utilized to significantly reduce the number of die prototype designs that are currently required in sheet metal stamping operations.

Influence of boric acid additive size on green lubricant performance

As the industrial community moves towards green manufacturing processes, there is an increased demand for multi-functional, environmentally friendly lubricants with enhanced tribological performance. In the present investigation, green (environmentally benign) lubricant combinations were prepared by homogeneously mixing nano- (20 nm), sub-micrometre- (600 nm average size) and micrometre-scale (4 μm average size) boric acid powder additives with canola oil in a vortex generator. As a basis for comparison, lubricants of base canola oil and canola oil mixed with MoS2 powder (ranging from 0.5 to 10 μm) were also prepared. Friction and wear experiments were carried out on the prepared lubricants using a pin-on-disc apparatus under ambient conditions. Based on the experiments, the nanoscale (20 nm) particle boric acid additive lubricants significantly outperformed all of the other lubricants with respect to frictional and wear performance. In fact, the nanoscale boric acid powder-based lubricants exhibited a wear rate more than an order of magnitude lower than the MoS2 and larger sized boric acid additive-based lubricants. It was also discovered that the oil mixed with a combination of sub-micrometre- and micrometre-scale boric acid powder additives exhibited better friction and wear performance than the canola oil mixed with sub-micrometre- or micrometre-scale boric acid additives alone.

Formulation and processing of novel conductive solution inks in continuous inkjet printing of 3-D electric circuits

One of the greatest challenges for the inkjet printing electrical circuits is formulation and processing of conductive inks. In the present investigation, two different formulations of particle-free conductive solutions are introduced that are low in cost, easy to deposit, and possess good electrical properties. A novel aqueous solution consisting of silver nitrate and additives is initially described. This solution demonstrates excellent adherence to glass and polymers and has an electrical resistivity only 2.9 times that of bulk silver after curing. A metallo-organic decomposition (MOD) ink is subsequently introduced. This ink produces a close-packed silver crystal microstructure after low-temperature thermolysis and subsequent high-temperature annealing. The electrical conductance of the final consolidated trace produced with the MOD ink is very close to bulk silver. In addition, the traces produced with the MOD material exhibit excellent wear and fracture resistance. When utilized in a specialized continuous inkjet (CIJ) printing technology system, both particle-free solution inks are able to produce conductive traces in three dimensions. The importance of three-dimensional (3-D) printing of conductive traces is finally discussed in relation to the broad range of applications in the freeform fabrication industry.

Mechanism of in vivo DNA transport into cells by electroporation: electrophoresis across the plasma membrane may not be involved

Recently, in vivo gene transfer with electroporation (electro‐gene transfer) has emerged as a leading technology for developing nonviral gene therapies and nucleic acid vaccines. The widely hypothesized mechanism is that electroporation induces structural defects in the membrane and provides an electrophoretic force to facilitate DNA crossing the permeabilized membrane. In this study, we have designed a device and experiments to test the hypothesis.

A JKR?DMT transition solution for adhesive rough surface contact

Utilizing Maugis–Dugdale transition theory and a procedure demonstrated by Fuller and Tabor, a solution is given for adhesive rough surface contact. The resulting solution includes adhesive forces of asperities that are in intimate contact and asperities that are not in contact but within the range of adhesion. This work further illustrates that adhesive overload can significantly increase frictional forces.

Investigation of the morphology of internal defects in cross wedge rolling

Abstract Since internal defects in the cross wedge rolling (CWR) process can weaken the integrity of the final product and may ultimately lead to catastrophic failure, it is necessary to investigate the mechanisms of their generation and growth. Using a specially designed CWR experimental apparatus, experiments were performed at more than 50 different operating conditions. The cross-sectional profiles of the workpiece specimens were examined and compared at each condition. Based on the experiments, the influence of three primary parameters in CWR process—the forming angle α , the stretching angle β , and the area reduction Δ A were determined. From the experimental results, the morphology of void generation and growth in CWR is ascertained and discussed. Through the definition of a non-dimensional deformation coefficient e , a method for predicting the likelihood of void formation is also established and discussed with respect to optimizing CWR tooling design.

Analysis of stress in cross wedge rolling with application to failure

In the present investigation, a previously developed three-dimensional finite-element model for the cross-wedge rolling (CWR) process has been used to characterize the workpiece material stress and deformation behavior. Particular attention has been paid to the center and mid-radius points of the billet where internal defects (i.e. internal cracks and porous voids) often occur. Several failure criteria in the solid mechanics theory are summarized. The effect of three important CWR parameters, namely the forming angle, the area reduction, and the friction coefficient, on the field variables has been investigated, including the first principal stresses, maximum shear stresses, etc. A total of 14 rolling conditions are analyzed for the billet material aluminum alloy 1100. After initially verifying the numerical results, several tendencies for the CWR process, as related to failure, are ascertained and discussed.

A finite element analysis of the frictional forces between a cylindrical bearing element and MoS2 coated and uncoated surfaces

Abstract Most precision positioning mechanisms and tracking systems contain instrument ball bearings that operate at ultra-low-speeds. Successful operation of these highly sensitive systems largely depends upon the ability to predict their bearing friction behavior. Until recently, very little research has been performed to understand the ultra-low-speed friction in coated bearings. Herein lies the scope of this paper: to develop a realistic finite element model which determines fundamental tribological friction relationships in coated bearings which are directly applicable to enhancing the control of precision systems. A brief review of the general friction response of bearings operating at ultra-low-speeds and the principles by which thin solid films reduce friction is given. As all of the work presented in this paper exclusively utilizes molybdenum disulfide as a solid lubricant film, the crystallographic structure, material properties and attributes of MoS 2 are discussed. A two-dimensional finite element model was developed to realistically characterize the friction experienced by a rolling element (i.e. a cylinder) confined between two parallel plates (representing bearing races). Experimental tests of a similar nature but with ball bearings were performed by the authors in a specially designed apparatus that allowed speeds as low as 0.001 deg −1 . Friction force results are presented for coated surfaces under several normal loads per unit length with steel and ceramic rolling elements. Using the results, general trends for the frictional behavior of coated bearing surfaces are established.

Tribology for Scientists and Engineers

Fundamentals of Engineering Surfaces.- Friction and Wear.- Contact Mechanics.- Experimental Methods in Tribology.- Interface Temperature of Sliding Surfaces.- Tribology of Metals and Alloys.- Tribology of Ceramics and Ceramic Matrix Composites.- Tribology of Metal Matrix Composites.- Coatings Tribology.- Fundamentals of Lubrication.- Self-Lubricating Behaviour of Graphite Reinforced Composites.- Particle Tribology.- Tribology of Solid Lubricants.- Tribology of Green Lubricants.- Nano Tribology.- Surface Probe Techniques.- Biotribology and Human Tribology.- Green and Biomimetic Tribology.- Fundamentals of Linking Tribology and Corrosion for Medical Applications.- Wear of Biomedical Implants.- Tribology in Metal Cutting.- Tribo-chemistry and Tribo-corrosion.- Tribology in Chemical-Mechanical Planarization.- Tribology in Metal Forming.- Tribology in Machine Components.- Macroscale Applications in Tribology.- Microscale Applications in Tribology.

Boundary element method analysis of temperature fields in coated cutting tools

Abstract Two general boundary element techniques are developed for determining the temperature fields in materials containing thin coatings. The first method utilizes a two-dimensional multi-domain approach that is accurate over a wide range of coating thicknesses. The second technique, which is based on a more computationally efficient single-layer approximation, is geared towards applications where the coating thickness is very small. After initially being verified with two simplified test cases, both methods are used to determine the temperature fields of coated and uncoated metal cutting tool inserts. Through generation of results for different coating materials (TiN, TiC, and Al 2 O 3 ) and by comparison with actual experimental data, the accuracy and applicability of the single-domain approximation and multiple-domain methods are discussed as related to machining processes.