George Haritos

An Analytical Model for the Identification of the Threshold of Stress Intensity Factor Range for Crack Growth

The value of the stress intensity factor (SIF) range threshold for fatigue crack growth (FCG) depends highly on its experimental identification. The identification and application of are not well established as its determination depends on various factors including experimental, numerical, or analytical techniques used. A new analytical model which can fit the raw FCG experimental data is proposed. The analytical model proposed is suitable to fit with high accuracy the experimental data and is capable of estimating the threshold SIF range. The comparison between the threshold SIF range identified with the model proposed and those found in the literature is also discussed. identified is found to be quite accurate and consistent when compared to the literature with a maximum deviation of 5.61%. The accuracy with which the analytical model is able to fit the raw data is also briefly discussed.

Factors Influencing the Performance of Porous Wind Shields

Porosity, porosity distribution, porous shape, porous size, thickness of shield, shield height &width, and shield orientation are the factors that influence the performance of porous wind shields. Among them, porosity is the most important factor in determining the performance of porous shields. However shield height & width have major impacts on the performance of shields. The remaining factors play less significant influences on the performance of the shield, but they remain researching interests to be further studied.

Advanced phase powertrain design attribute and technology value mapping

Purpose – The purpose of this paper is to focus on how the concept design stage of a powertrain system can be improved by using a purely objective driven approach in selecting a final concept design to progress further. This research investigation will examine the development of a novel test-bed to assist in the selection of powertrain technologies during the concept design phase at Ford Motor Company Ltd, serving as the main contribution to knowledge. Design/methodology/approach – The objectives of this research were achieved by carrying out a literature review of external published work related to concept design evaluation methods within product development and value engineering techniques. Empirical studies were conducted with a supporting case study used to test the application of a new test-bed to improve the concept design decision process. Findings – A quantitative new tool “Product Optimisation Value Engineering” (PROVEN) is presented to critically assess new and evolving powertrain technologies a...

Investigation of vehicle ride height and diffuser ramp angle on downforce and efficiency

Diffusers are typically used in motorsport to generate negative lift (downforce). They also reduce aerodynamic drag and so significantly enhance aerodynamic efficiency. The amount of downforce generated is dependent on ride height, diffuser ramp angle and its relative length to that of the vehicle length. This paper details a numerical investigation of the effects of ride height and diffuser ramp angle in order to find an optimum downforce and efficiency for the inverted Ahmed model. A short and long diffuser with ratios of 10% and 35%, respectively, to that of vehicle length are studied. The short diffuser produced lower maximum downforce and efficiency at a lower ride height and lower angle when compared to the longer diffuser. The long diffuser produced highest downforce and the best efficiency with a ramp angle of 25° at ride height ratio of 3.8% when compared to vehicle length. Different ride heights were found to correspond to different diffuser ramp angles to achieve optimum downforce and efficiencies.

Attribute and technology value mapping for conceptual product design phase

The main focus of this paper is how the concept design phase of the product development process can be improved by using an objective data-driven approach in selecting a final concept design to progress further. A quantitative new test-bed ‘Product Optimisation Value Engineering’ (PROVEN) is presented to critically assess new and evolving powertrain technologies at the concept design phase. The new test-bed has the ability to define a technology value map to assess multiple technical options as a function of its attributes, whose precise values can be determined at a given cost. A mathematical model that incorporates a highly adaptable, data-driven and multi-attribute value approach to product specification and conceptual design is developed, novel to the concept design process. This creates a substantially optimised product offering to the market, reducing overall development costs while achieving customer satisfaction.

Spatial Prediction of a Pre-curved Bimetallic Strip Under Combined Loading

This work establishes a way of calculating the free end point position, of a pre-curved bimetallic strip, that is subjected to uniform heating. The prediction of the endpoint of a bimetallic strip is required during the design phase of an electronic control circuit sensor switch that uses a sensing/activating unit containing a bimetallic strip. Bimetallic sensors are normally flat at ambient temperature and at the required sensing temperature the strip bends into a radius of curvature, this then displaces the contact on the end of the strip to make or break an electrical circuit. Although the normal, flat type of bimetallic sensor exists, this work concentrates on a pre-curved bimetallic sensor at ambient temperature. A curved bimetallic strip sensor provides a much larger sensing range and displacement at the free end of the strip, per degree of temperature change, than for a straight bimetallic strip. The greater sensing range is due to the arc length of the bimetallic strip being longer which affords a greater flexibility at the activation point when compared to the chord length of an equivalent straight bimetallic strip. Pre-curved bimetallic test samples were subjected to heating whilst the motion of the free end point of the strip was recorded on a metal plate. As the heat applied to the samples was increased, many temperature points were recorded to generate approximate loci of points. The loci of test points compared well to theoretical curve generated by the derived formulae. Therefore the advantages of this work offers a less critical sensing range, it also benefits from a mechanism which can be designed to be much smaller and take less space in the product compared to a comparable flat bimetallic strips sensor.

Delamination Threshold Load of Composite Laminates under Low-Velocity Impact

A key factor affecting the use of carbon fibre reinforced composite laminates is the low velocity impact damage which may be introduced accidentally during manufacture, operation or maintenance of the component. Among the several barely visible impact damages, interlaminar delamination is the dominant failure mode and may reduce the post-impact compressive strength of the component significantly. This paper focuses on the study of the delamination threshold load (DTL) above which significant increase of delamination and thus large reduction of the residual compressive strength of the component may occur. Instrumented drop weight tests were carried out under various impact energy levels to determine the delamination threshold load. Efforts are directed to the study of the laminate thickness effect on the reliability of the detection of the DTL. The validity of the concept of DTL has been investigated and possible implications on the measurement of the DTL has been discussed. It is demonstrated that DTL exists but its detection requires proper testing conditions.

Modular system for methodological design of body assemblies

The University of Applied Sciences (HAW) Hamburg and the University of Hertfordshire in collaboration with the automotive industry set up a R&D process to optimise the design methods in the “new” parametric associative approach. The objective with the parametric associative design was to develop new methods for task allocation and a more “structured” approach in the organisation of design processes while designing automotive body components. Groups consisting of four to seven students evaluated and developed body assemblies. 22 realistic projects were identified before by automotive companies. Here, important conclusions are presented for the example A-pillar.

Baukastensystem zur systematischen Konstruktion der Baugruppen einer Karosserie

Die HAW Hochschule fur angewandte Wissenschaften Hamburg und die University of Hertfordshire etablierten in Zusammenarbeit mit der Automobilindustrie einen Entwicklungsprozess, um die Konstruktionsmethoden fur die „neue“ parametrisch-assoziative Arbeitsweise zu optimieren. Ziel mit der parametrisch-assoziativen Konstruktion war es, neue Methoden zur Konstruktion der Baugruppen, Verteilung der Aufgabenstellung und Organisation der Konstruktionsprozesse zu untersuchen. Gruppen von jeweils vier bis sieben Studierenden bewerteten und entwickelten Baugruppen der Karosserie. 22 realitatsnahe Projekte waren zuvor von Firmen der Automobil industrie identifiziert worden. Hier werden wichtige Erkenntnisse am Beispiel der A-Saule dargestellt.