Papers by chris Rodopoulos
Based on the principles of the Fatigue Damage Map, the effect of the stress ratio, R, on the boun... more Based on the principles of the Fatigue Damage Map, the effect of the stress ratio, R, on the boundaries of short crack growth is investigated. The analysis reveals that the tendency of the material to short crack growth is governed by the relation between the fatigue limit, σFL, and the cyclic yield stress, σcy. Materials with low values of w=σFL/σcy loaded at high values of R exhibit negligible amount of growth irregularities, allowing therefore the accurate representation by a Paris-Erdogan power law.
The world averaged values of the electroweak and strong couplings and the lower limits on the pro... more The world averaged values of the electroweak and strong couplings and the lower limits on the proton lifetime are used for consistency checks of Grand Unied Theories (GUT). It is conrmed that new physics outside the Standard Model (SM) is required to obtain unication of the electroweak and strong forces. Such new physics could come from the minimal supersymmetric extension of the SM, which provides unication consistent with the present limits on the proton lifetime, but non-supersymmetric models based on additional split multiplets show similar unication properties. The unication condition strongly restricts the number of GUT's, but cannot distinguish between them. Only future experiments will be able to do so.
International Journal of Structural Integrity
Purpose The purpose of this paper is to demonstrate the effect of accelerated environmental loadi... more Purpose The purpose of this paper is to demonstrate the effect of accelerated environmental loading, i.e. humidity, solar radiation, wet/dry cycling, CO2 concentration and temperature on specimens being initially protected using 4 commercially available coating systems and to evaluate their degradation considering the results. Design/methodology/approach For the purpose of the study, an accelerated environmental loading was performed in a highly sophisticated chamber able to replicate weather patterns representing the 8 characteristic climate zones of Australia. Findings The results in terms of degradation patterns can provide a qualitative classification leading to the development of a Dynamic Protection Index Factor (DPIF) which can be used as direct input in life cycle cost analysis appraisal. Originality/value This paper is considered to be very important, since the degradation results of different environmental conditions constiture a major problem for structures life inspectio...
Theoretical and Applied Fracture Mechanics, Feb 1, 2009
This paper examines cracking in D6ac and 4340 steel along with Mil Annealed and STOA Ti-6Al-4V an... more This paper examines cracking in D6ac and 4340 steel along with Mil Annealed and STOA Ti-6Al-4V and finds that the data implies that in the Paris Region (Region II) of the crack growth curve there is only a minimal R ratio dependency. Presented is a theoretical basis for explaining this behaviour and suggest alternative ways for characterising crack growth prediction through the use of the Generalised Frost-Dugdale crack growth law. The Fatigue Damage Map method is then used to explain the physics behind this behaviour.
Theoretical and Applied Fracture Mechanics, Jun 1, 2006
Using only readily available material properties and the concept of the fatigue damage map the wo... more Using only readily available material properties and the concept of the fatigue damage map the work attends to develop a methodology able to predict crack tip propagation rates characterising each of the fatigue stages, namely crack arrest, microstructurally and physically short crack (Stage I), long crack growth (Stage II) and Stage III growth. Crack tip propagation rates are predicted through the combination of an Elasto-Plastic crack tip opening displacement model and the crack blunting theory. The methodology provides a theoretical framework for a 3D version of the fatigue damage map for damage tolerance design. In addition, the work attends to explain a number of fundamental problems starting from crack tip propagation discrepancies, found in the short cracking stage, as well as to provide an insight towards the effect of grain size on the fatigue limit/threshold stress intensity factor.
For many years the corrosion resistance of aluminium alloys used in aeronautical components have ... more For many years the corrosion resistance of aluminium alloys used in aeronautical components have been examined at room temperature. Yet, the great majority of military aircraft, especially those operating from aircraft carriers experienced significant heat input commonly named deck deflection heat. From data collected from the US Navy, the actual temperature at the lower wing can reach temperatures in excess of 100 degrees C. At these temperatures the protection provided by the clad film is critically lowered with significant effects to the structural integrity of the aircraft. Testing performed at elevated temperatures has shown that the rate of clad reduction is 5 times faster at 80 degrees than at 20. Solution to the problem has been sought through the use of Ultrasonic Impact treatment. The technology enables the nanocrystalisation of the surface to a depth of 30 microns. Corrosion tests at different elevated temperatures without the use of clad film has shown that surface nanocrystalisation can provide improvement over 300% in the creation of pitting, general corrosion and exfoliation damage.
Page 1. Problems of Fracture Mechanics and Fatigue A Solution Guide Edited by EE Gdoutos CA Rodop... more Page 1. Problems of Fracture Mechanics and Fatigue A Solution Guide Edited by EE Gdoutos CA Rodopoulos JR Yates Klimer Academic Publishers Page 2. Page 3. List of Contributors Afaghi-Khatibi, A., Department of Mechanical and Manufacturing Engineering. ...
Summary The present investigation has been made as part of an ongoing study into the effects of C... more Summary The present investigation has been made as part of an ongoing study into the effects of CSP. Aluminium alloy 2024 T351 is commonly used within the aerospace industry, and is routinely shot peened as part of the manufacturing process. To determine the effects of CSP on the corrosion fatigue behaviour of this alloy, a series of tests were performed. Initially, corrosion fatigue tests were conducted on both unpeened and peened specimens. Electrochemical testing was then undertaken, firstly, to investigate if the shot peening ...
The concept of the Fatigue Damage Map (FDM) is used to establish the domains of different crack g... more The concept of the Fatigue Damage Map (FDM) is used to establish the domains of different crack growth regimes, namely, crack arrest, short crack growth, steady-state crack growth and Stage III crack growth, general yielding and toughness failure. In this work the concept of the FDM is extended to incorporate the effects of fretting fatigue. This is achieved by introducing an equivalent crack length to account for the multi-axiality of the loading and the orientation of the crack plane. In addition, a micromechanical notch sensitivity model is introduced to account for the wear damage.
Fracture of Nano and Engineering Materials and Structures, 2006
ABSTRACT The practise of identifying corrosion damage, air-blasting to remove loose material, gri... more ABSTRACT The practise of identifying corrosion damage, air-blasting to remove loose material, grinding to remove corrosion, shot peening to increase the fatigue properties and finally back assembly onto the aircraft for many years has governed aircraft operators under the term “find and fix”. This empirical practise inevitably causes thickness and hence load bearing reduction while can locally overstress components. To avoid that a rule of thumb is implemented making sure that no more than 10% of the initial thickness of the material has been lost. Otherwise, the component should be replaced. It is not difficult to understand that such practise primarily lies within the expertise of the person performing the repair as well as the geometric complexity of the damage. If the corrosion damage is situated at a location which is difficult to grind or, and to peen then most certainly the quality of the repair will vary. The problem can have significant implication under cyclic loading considering that the residual stresses induced by shot peening will undergo continuous redistribution as part of their relaxation process, while irregular thicknesses can transform the design philosophy used for that component from safe life to fatigue damage tolerance. Herein, such repairs can start fatigue cracks following local stress raisers, due to stiffness loss especially when close to stiffeners or by redistributing shear strains when close to joints. The Ultrasonic Impact Treatments process is employing continuous ultrasonic vibrations at the ultrasonic transducer output end strengthened with hard materials (carbide-containing alloys, artificial diamonds etc.) and being in direct and generally continuous contact with the treated surface. During impact the near surface of the material experiences high strain rates as well as heating. The first is responsible for plastically deforming the material.
Solid Mechanics and its Applications, 2008
ABSTRACT The work continuous with the Fatigue Damage Map Method (FDMM) that attempts to unify the... more ABSTRACT The work continuous with the Fatigue Damage Map Method (FDMM) that attempts to unify the propagation rates with the concept of the effective plastic strain. Reference is made to the local strain characterizing the crack tip modified to include the variation of flow resistance as a function of crack length. Comparison with experimental data of multiscale crack growth rates is provided.
Fracture of Nano and Engineering Materials and Structures, 2006
ABSTRACT Short or Stage I crack growth represents a unique case where the Paris-Erdogan Linear El... more ABSTRACT Short or Stage I crack growth represents a unique case where the Paris-Erdogan Linear Elastic Fracture Mechanics model fails to predict crack growth and hence fatigue life. The propagation rate of short cracks has been found in numerous works and for a variety of materials to be significantly higher than that predicted by the aforementioned model [1],[2]. Yet, there is a strong relation between the material and the extent of short cracking. In general, aluminium alloys exhibit a much larger short cracking potential to high strength steels. In addition, stress ratio has also been found to play an important role on such phenomenon [3]. In brief, the extent of short cracking has been found to decrease with the stress ratio and even disappearing after a particular value [4]. In a number of papers Rodopoulos and co-workers argued that the phenomenon depends on the ratio between the fatigue limit and the cyclic yield stress [5], as shown in Figure.1.
Recent Advances in Experimental Mechanics, 2004
ABSTRACT
Recent Advances in Composite Materials, 2003
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Papers by chris Rodopoulos