David Cebon

Selection strategies for materials and processes

Abstract Engineering design draws on tens of thousands of materials and on many hundreds of processes to shape, join and finish them. One aspect of optimized design of a product or system is that of selecting, from this vast menu, the materials and processes that best meet the needs of the design, maximizing its performance and minimizing its cost. The problem, still incompletely solved, is that of matching material and process attributes to design requirements. Some of these attributes can be expressed as numbers, like density or thermal conductivity; some are Boolean, such as the ability to be recycled; some, like resistance to corrosion, can be expressed only as a ranking (poor, adequate, good, for instance); and some can only be captured in text and images. Achieving the match with design requirements involves four basic steps. (1) A method for translating design requirements into a specification for material and process. (2) A procedure for screening out those that cannot meet the specification, leaving a subset of the original menu. (3) A scheme for ranking the surviving materials and process, identifying those that have the greatest potential. (4) A way of searching for supporting information about the top-ranked candidates, giving as much background information about their strengths, weaknesses, history of use and future potential as possible. In this paper we review the strategies that have evolved to deal with this problem, the progress that has been made and the challenges that remain.

Active Roll Control of Single Unit Heavy Road Vehicles

Summary Strategies are investigated for controlling active anti-roll systems in single unit heavy road vehicles, so as to maximise roll stability. The achievable roll stability improvements that can be obtained by applying active anti-roll torques to truck suspensions are discussed. Active roll control strategies are developed, based on linear quadratic controllers. It is shown that an effective controller can be designed using the LQG approach, combined with the loop transfer recovery method to ensure adequate stability margins. A roll controller is designed for a torsionally flexible single unit vehicle, and the vehicle response to steady-state and transient cornering manoeuvres is simulated. It is concluded that roll stability can be improved by between 26% and 46% depending on the manoeuvre. Handling stability is also improved significantly.

Dynamic interaction between heavy vehicles and highway bridges

Abstract This paper discusses the importance of dynamic interaction (coupling) between heavy vehicles and highway bridges. A new method for calculating the dynamic response of bridges to dynamic wheel loads is presented, and used to investigate a simply-supported bridge traversed by a single degree of freedom vehicle model. Six non-dimensional parameters of the bridge-vehicle system are varied to assess the amount of interaction between the vehicle and the bridge. Guidelines are presented to ascertain when dynamic interaction is important and when it can be ignored.

Truck suspension design to minimize road damage

The objective of the work described in this paper is to establish guidelines for the design of passive suspensions that cause minimum road damage. An efficient procedure for calculating a realistic measure of road damage (the 95th percentile aggregate fourth power force) in the frequency domain is derived. Simple models of truck vibration are then used to examine the influence of suspension parameters on this road damage criterion and to select optimal values. It is found that to minimize road damage a suspension should have stiffness about one fifth of current air suspensions and damping up to twice that typically provided. The use of an anti-roll bar allows a high roll-over threshold without increasing road damage. It is thought that optimization in the pitch-plane should exclude correlation between the axles, to ensure that the optimized suspension parameters are robust to payload and speed changes. A three-dimensional ‘whole-vehicle’ model of an air suspended articulated vehicle is validated against measured tyre force histories. Optimizing the suspension stiffness and damping results in a 5.8 per cent reduction in road damage by the whole vehicle (averaged over three speeds). This compares with a 40 per cent reduction if the dynamic components of the tyre forces are eliminated completely.

Vehicle-Generated Road Damage: A Review

SUMMARY The literature concerned with road damage caused by heavy commercial vehicles is reviewed. The main types of vehicle-generated road damage are described and the methods that can be used to analyse them are presented. Attention is given to the principal features of the response of road surfaces to vehicle loads and mathematical models that have been developed to predict road response. Also discussed are those vehicle features which, to a first approximation, can be studied without consideration of the dynamics of the vehicle, including axle and tyre configurations, tyre contact conditions and static load sharing in axle group suspensions. The main emphasis of the paper is on the dynamic tyre forces generated by heavy vehicles: their principal characteristics, their simulation and measurement, the effects of suspension design on the forces and the methods that can be used to estimate their influence on road damage. Some critical research needs are identified.

Biocompatibility: Meeting a Key Functional Requirement of Next-Generation Medical Devices

The array of polymeric, biologic, metallic, and ceramic biomaterials will be reviewed with respect to their biocompatibility, which has traditionally been viewed as a requirement to develop a safe medical device. With the emergence of combination products, a paradigm shift is occurring that now requires biocompatibility to be designed into the device. In fact, next-generation medical devices will require enhanced biocompatibility by using, for example, pharmacological agents, bioactive coatings, nanotextures, or hybrid systems containing cells that control biologic interactions to have desirable biologic outcomes. The concept of biocompatibility is moving from a “do no harm” mission (i.e., nontoxic, nonantigenic, nonmutagenic, etc.) to one of doing “good,” that is, encouraging positive healing responses. These new devices will promote the formation of normal healthy tissue as well as the integration of the device into adjacent tissue. In some contexts, biocompatibility can become a disruptive technology that can change therapeutic paradigms (e.g., drug-coated stents). New database tools to access biocompatibility data of the materials of construction in existing medical devices will facilitate the use of existing and new biomaterials for new medical device designs.

EXPERIMENTAL STUDY OF PURE BITUMENS IN TENSION, COMPRESSION, AND SHEAR

Two nominally identical pure bitumens, commonly employed for pavement construction in the United Kingdom, were tested in uniaxial tension, compression, and shear, over a wide range of temperatures, stresses, and strain rates. The bitumens were found to exhibit linear viscous behavior at low stress levels, and power-law creeping behavior at higher stress levels. The temperature dependence was found to follow the Arrhenius relationship at temperatures immediately above the glass transition and the Williams, Landel, and Ferry (WLF) equation at higher temperatures. Below the glass transition temperature, the Eyring plasticity model was found to hold. Constitutive models that reflect the physical mechanisms of steady state and transient deformation are proposed. The fracture properties of the bitumens are also discussed.

Force Control of a Semi-Active Damper

SUMMARY Two strategies are investigated for controlling a semi-active damper to track a prescribed force demand signal: (i) ‘open loop’ control, using a model of the damping force versus velocity characteristics; and (ii) force feedback (closed loop) control. The damping characteristics and switching transients of a prototype damper were measured, and used to develop a mathematical model of the dynamics of the damper. The two control strategies were investigated using an idealised (constant velocity) test. Their performance was also simulated and measured under realistic operating conditions using the Hardware-in-the-Loop testing method. Open loop damper control was generally found to give superior performance to force feedback control, due to its smaller phase lag at high frequencies.

Performance of a Semi-Active Damper for Heavy Vehicles

This paper describes the development, modeling, and testing of a prototype, continuously variable semi-active damper for heavy vehicles. A simple proportional valve is used to generate the variable damping coefficient and the detrimental effects of the oil flow forces acting on the valve spool are studied. The force tracking performance of the damper is then examined under simple input conditions. The compliance of the hydraulic fluid is found to have a strong influence on the response of the damper. The performance of the prototype damper is investigated under realistic operating conditions using a Hardware-in-the-Loop (HiL) test rig, with a single wheel station vehicle model. The prototype damper displays a time lag of approximately 20 ms between the demanded and achieved damping force. The semi-active suspension is found to be most effective in reducing the vehicle body motion relative to the performance of an optimum passive suspension.

Improving roll stability of articulated heavy vehicles using active semi-trailer steering

This paper discusses an optimal linear quadratic control algorithm to improve the roll stability of a tractor semi-trailer using active semi-trailer steering. The controller minimises a combination of the path-tracking deviation of the trailer rear end relative to the path of the hitch point (5th wheel) and the lateral acceleration of trailer centre of gravity (CoG). First a linear vehicle model of tractor semi-trailer is constructed. Then a ‘virtual driver’ model for trailer steering control is introduced to minimise the path-tracking deviation of trailer rear end. The lateral acceleration of trailer CoG is included as a second objective of the optimal controller so as to improve roll stability. A Kalman filter with linear vehicle model is used to estimate unknown vehicle states, needed by the controller. Simulation results show that optimal control of semi-trailer steering could improve the roll stability significantly during transient manoeuvres while keeping the path-tracking deviation of trailer rear end within an acceptable range.