Some works fulfilled by using FEM analysis
Numerical simulation of the interface bond strength of substrate/coating interfaces based on the Laser Induced Spallation technique. Co-development of the Laser Induced Spallation facility and measurement of the bond strength of planar interfaces between various substrates and thin metallic or ceramic coatings. Development of its numerical simulation based on the simultaneous solution of the Radiation Hydrodynamic equations and Equations of State (EOS). Implementation of the absorption of laser light and the SESAME EOS (obtained from Los Alamos National Laboratory) in the LS-DYNA2D. A number of wave propagation and spallation studies were performed towards this end. (1993-1996).
Development of new medical tools for the early medical prognosis and biotechnological applications - Early Prognosis of Brain Edema Determination of the eigenfrequency spectrum of a fluid-solid interaction system described with viscoelastic constitutive equations representing the skull - brain system. The LLNL-NIKE2D linked with the IMSL Math Libraries as well as the MSC-NASTRAN FEA code were used to provide solution to the complex eigenvalue formulation that results from the FSI system. (1996–1997).
Residual Stress Investigation in Aluminium Ring&Plug and CMCs
Analytical and finite element calculations in order to have a quantitative estimate of the residual stresses in Aluminium Ring and Plug and Ceramic Matrix Composite Round Robin Specimens used as calibrants in the SMT4-CT97-2200 Residual Stress Standard using Neutron Diffraction program. The project was co-ordinated by JRC and aims to resolve measurement problems and bring about harmonisation of test methods across Europe in aerospace, energy and nuclear industries. The FEA work was performed using LLNL-NIKE2D & NIKE3D. (1997-2000)
Picosecond Laser Induced Spallation of thin films and coatings
Extend the use of Laser Induced Spallation Technique for interface strength measurements for sub-micron thick metallic and ceramic coatings. Numerical optimization studies were performed using the modified LS-DYNA2D (cf. previous project – PhD) based on the interaction of picosecond laser light pulses and matter as well as stress wave propagation and fracture of the coating by spalling. Development of software for the post processing of the free surface velocity profile of the coating as measured with a Laser Doppler Interferometer - VISAR. (1997-2000)
Methodology for life prediction and condition assessment for welds of refurbished and new steam cycle plants (BE96-3019) - LICON
Stress analysis and fracture mechanics FEA calculations were performed in P92 pressure vessels based on the unified viscoplasticity and continuum damage mechanics theories. The analysis was performed with ZEBULON and the Bammann’s viscoplastic constitutive equation within LS-NIKE2D was modified to verify the results obtained from ZEBULON. (1997-2000).
Design by Analysis (DBA) for new standards in a nozzle in spherical end with cold-media injection
Stress analysis FEA calculations were performed in a nozzle in order to check if the maximum allowable pressure, determined by Design by Formula (DBF), ensures the design checks against Gross Plastic Deformation (GPD), Progressive Plastic Deformation (PD) and Shakedown (SD) according to Design by Analysis (DBA). The work was part of the DBA-WP3 project aimed at a new European Standard (CEN-TC54) for the calculation and manufacture of pressure equipment. LS-NIKE2D and TOPAZ2D were used for the analysis. (1997-2000).
Structural assessment of gladded vessels under the Network for Evaluating Steel Components (NESC-II)
Round robin stress analysis FEA calculations were performed as part of the structural assessment of shallow crack behaviour in a gladded vessel under pressurised thermal shock (PTS) loading with regard to brittle crack initiation, propagation and arrest. The analysis was performed using ABAQUS, WARP3D and LS-NIKE3D codes. (1997–2000).
Lifetime prediction methodology in Thermal Barrier Coatings (TBCs)
A research effort towards experimental characterisation, numerical verification and lifetime prediction of TBCs. The modelling work performed was in support to experiments and includes: plasma spray deposition process, development of primary (quenching) and secondary (residual) stresses, inverse thermal diffusivity calculations from Laser flash technique in microcracked PS-TBCs, micro-indentation towards elastic modulus determination, vibrational analysis towards damage identification, constitutive modelling of IN738 based on unified viscoplasticity, modelling of failure mechanisms (free edge effects, roughness of the bond-coat/TBC interface, TGO presence). All numerical calculations were performed using the LS-NIKE2D and LS-NIKE3D FEA codes. (1997-2000).
Stress transfer assessment in Continuous Fibre Ceramic Composites (CFCCs)
The influence of interfacial shear stiffness, fiber breakage and interfacial debonding or matrix cracking on stress transfer in SiC/SiC has been studied numerically. (1997-2000)
Numerical optimization of the Sheet Metal Forming process of a doubly curved part of an aircraft leading edge
Under contract from the STORK-Fokker Aerospace Structures, finite element analysis and design were performed towards a proposed optimized path of the grips during the sheet metal stretching of a complicated doubly curved wing panel. The model takes into account phenomena like springback, anisotropic initial and updated yield locus, crystal plasticity and annealing. The work was performed using the LS-DYNA v.960. (2000-2002).
Impact of tensor skin aircraft panels
Develop models to access the impact damage of spherical indentors upon composite tensor skin panels. The project aims to verify previously performed experimental studies with an eye towards optimization of future designs. The work was performed using the LS-DYNA v.960. (2000 – 2002)
GARTEUR Bird Strike Impact - Numerical simulation upon metallic and composite aircraft panels
Modelling of bird strike impact on flat and wing shaped metal and composite panels in the context of the GARTEUR (Group for Aeronautical Research and Technology in EURope). A new methodology combining the concepts of Higher Order Shear Deformation Theories of shell structures and a delamination capable interface are being implemented in the LLNL-DYNA3D FEA code. The sensitivity of the Equation of State for the substitute artificial bird is also evaluated. (2000–2003)
Design of the backup telescopic landing gear of the ROSETTA spacecraft
Under contract for Brandford Eng., and ESA preliminary and detailed analysis was performed for the backup landing gear system of the ROSETTA spacecraft (ESA) towards its rendezvous with the comet Wirtanen. The author was responsible for the final detailed FEA of the impact of the ROSETTA satellite against the comet and the safe cycle determination of the rebound effect until the harpoons are fired and lock the satellite to the comets surface. The work was performed using the LS-DYNA v.960. (2000 – 2003)
Frangability analysis and design of Airport Light Approach Structures
Under contract for the Dutch Civil Aviation Authority (RLD) and a Canadian Company, parametric numerical studies were performed to access the impact damage of light aeroplanes against typical approach lighting structures at airports. The work was performed using the LS-DYNA v.960 and aims to minimize the damage in a typical aircraft wing panel if impacted with the Airport Light Approach Structures such as the ILS towers. (2000 – 2003)
A vehicular heavy duty Composite Bridge made of Glass/Polyester pultruded Box Beams
This work deals with the design, analysis, optimization and construction of a vehicular bridge made of glass reinforced polyester pultruded box beams.
The bridge is of 12 m span and 4m width and represents a one strip-loading lane. The load bearing capacity of the bridge is 300 kN. The composite bridge is consisted by a 3-D truss structure made of two layer one-shot, thick wall FRP longitudinal box elements of hollow square cross section, which are bridged together with box-beams of the same geometry.
A continuous monitoring of the structural integrity of the composite bridge has been applied by using vibration analysis techniques and periodic Acoustic Emission monitoring. The total weight of the composite bridge does not exceed the 135 kN while its expected service life is 50 years. (1999-2002).
Finite Element Analysis of Impact Damage Response of Composite Motorcycle Safety Helmets
The energy absorption during impact provided by a motorcycle safety helmet is always of critical importance in order to protect the rider against head injury during an accident. In this study, a parametric analysis has been performed in order to investigate the effect of the composite shell stiffness and the damage development during impact, on the dynamic response of a composite motorcycle safety helmet. This kind of parametric analysis may be used as a tool during helmet design for minimising testing needs (2002-2004).
The LS-DYNA3D explicit hydrodynamic finite element code was used to analyse a detailed model of the helmet-headform system (composite shell/foam liner/metallic headform) and to simulate its dynamic response during impact. A significant part of the work was focused on the modelling of the mechanical behaviour of the composite materials, including damage and delamination development. The dynamic response of the different helmet-headform systems was judged in terms of the maximum acceleration monitored at the centre of gravity of the headform and the maximum value of Head Injury Criterion (HIC).
It was shown that composite shell systems exhibiting lower shear performance provide additional energy absorbing mechanisms and result to better crashworthiness helmet behaviour. (1999-2001).
A New Design Methodology for High Temperature Structural Components made of Continuous Fiber Ceramic Composites exhibiting thermally induced Anisotropic Damage
Continuous Fiber Ceramic (Matrix) Composites (CFCCs) have found during the last decade numerous industrial applications in a variety of technological areas, where structural components are subjected to high temperature combined with significant mechanical loading.
The present work deals with the application of innovative design methodologies for the development of an industrial gas turbine combustor chamber made of oxide/oxide composite materials.
Oxide/oxide composites offer high-temperature structural stability without the need of any kind of oxidation protection and thus permit the increase of working temperature of the gas turbines, increasing the efficiency of the system and decreasing the need for cooling air and the NOx emissions.
Since, oxide/oxide composites appear degradation of their structural properties as a function of the operating temperature (for temperature higher than 1000o C) and the exposure time, an incremental approach has been introduced for the solution of the problem and each increment represents a thermal exposure stage. The structure has been divided in temperature zones and a mean working temperature was considered for each zone. The data set required for the application of the present design methodology were obtained through an extensive material characterization program based on the measurement of the anisotropic properties of oxide/oxide composites using ultrasonic techniques. ANSYS & NIKE commercially available FEM codes have been used for the solution of the problem and the necessary material constitutive laws have been developed accordingly. (1999-2003).
Numerical simulation of high and low velocity impact upon composite laminates structures
The damage assessment of composite aerospace structures is investigated. A number of delamination prone stacking sequence CFRP plates were examined. The LLNL DYNA3D was used and modified to accommodate three different failure criteria as well as convenient printing (D3HSP) and plotting (D3PLOT) of fiber failure, matrix cracking and delamination. (2004).