The trend in aircraft design is to produce greener airplanes through lighter structures and/or structures with extended life and reduced maintenance. Bonded crack retarders (BCR) are one of the solutions towards that objective. BCR are reinforcing straps bonded to the structure in order to improve the fatigue and damage tolerance properties of the assembly. The aim of this study was to demonstrate that the BCR hybrid technology – beneficial for upper wing cover – could also be applied to lower wing covers. The project also focused on evaluating BCR most important parameters. The fatigue life improvement obtained from BCR was evaluated through a series of coupons and skin-stringer assemblies tested under constant and variable amplitude loading. While the coupon tests demonstrated a life improvement of only 17% under constant amplitude loading, the variable amplitude load tests performed on the skin-stringer assembly demonstrated increased fatigue lives with a factor of 5 and reduced crack growth rates with a factor of 5 to 6. A finite element calculation tool was developed in order to conduct a parametric analysis of BCR geometry through the evaluation of the substrate stress intensity factor in the case of fatigue loading. The main difficulty was to include the interacting mechanism of the substrate lead crack and the disbond of the adhesive layer. The novelty of the approach was to incorporate the fatigue delamination calculation in order to evaluate the fatigue disbond propagation with crack growth. This was embedded in a 3D finite element design tool ReSLIC (Reinforced Structures Life Improvement Calculation). A necessary step to the development of ReSLIC was the analysis of fatigue properties of the adhesive system in order to provide input data for fatigue delamination calculations. To that end, a series of fatigue tests were performed in pure Mode I, pure Mode II and mixed mode with ratios of 25%, 50% and 75% of mode II ... [cont.].

A ênfase deste t rabalho está vol tada à utilização da simulação computacional dentro do contexto do processo de desenvolvimento de produto. Foi utilizado o método dos elementos finitos para simular o teste de bancada que é realizado para val idar a resistência mecânica e a capacidade de absorção de energia de estruturas de proteção contra capotamento (EPCC) de t ratores agrícolas. Foi feita uma proposta de design de uma cabina para t ratores estreitos e a parti r dela foi executado o teste vi rtual para a sua validação. A simulação foi fei ta considerando as característ icas não lineares dos materiais, uma vez que a deformação atinge o regime plástico dos mesmos. Como a cabina é uma est rutura soldada relativamente complexa, foram feitas idealizações para se reduzi r o tempo computacional. De posse dos resultados vi rtuais, foi possível prever as regiões mais e menos solici tadas da estrutura sem a necessidade de real izar o teste real, propondo assim alterações de design e de materiais da cabina para tornar a absorção da energia de deformação mais eficiente. / The emphasis of this work is focused on the use of computer simulation within the context of product development. The finite element method was used to simulate the real test that is conducted to validate the st rength and energy absorption capacity of rollover protective st ructures (ROPS) of agricul tural tractors. From a design proposal of a cab to a narrow tractor, the test was performed to validate it . The simulation was made by adopt ing the nonlinear characteristics of the materials, since the deformation reaches the plastic regime. As the cab is a welded structure relatively complex, idealizations were made to reduce the computational time. With the results vi rtual , it was possible to predict the most and least requested regions of the st ructure without the need to run the real test, proposing design and material changes to make the absorption of strain energy more efficiently.

A ênfase deste t rabalho está vol tada à utilização da simulação computacional dentro do contexto do processo de desenvolvimento de produto. Foi utilizado o método dos elementos finitos para simular o teste de bancada que é realizado para val idar a resistência mecânica e a capacidade de absorção de energia de estruturas de proteção contra capotamento (EPCC) de t ratores agrícolas. Foi feita uma proposta de design de uma cabina para t ratores estreitos e a parti r dela foi executado o teste vi rtual para a sua validação. A simulação foi fei ta considerando as característ icas não lineares dos materiais, uma vez que a deformação atinge o regime plástico dos mesmos. Como a cabina é uma est rutura soldada relativamente complexa, foram feitas idealizações para se reduzi r o tempo computacional. De posse dos resultados vi rtuais, foi possível prever as regiões mais e menos solici tadas da estrutura sem a necessidade de real izar o teste real, propondo assim alterações de design e de materiais da cabina para tornar a absorção da energia de deformação mais eficiente. / The emphasis of this work is focused on the use of computer simulation within the context of product development. The finite element method was used to simulate the real test that is conducted to validate the st rength and energy absorption capacity of rollover protective st ructures (ROPS) of agricul tural tractors. From a design proposal of a cab to a narrow tractor, the test was performed to validate it . The simulation was made by adopt ing the nonlinear characteristics of the materials, since the deformation reaches the plastic regime. As the cab is a welded structure relatively complex, idealizations were made to reduce the computational time. With the results vi rtual , it was possible to predict the most and least requested regions of the st ructure without the need to run the real test, proposing design and material changes to make the absorption of strain energy more efficiently.

A ênfase deste t rabalho está vol tada à utilização da simulação computacional dentro do contexto do processo de desenvolvimento de produto. Foi utilizado o método dos elementos finitos para simular o teste de bancada que é realizado para val idar a resistência mecânica e a capacidade de absorção de energia de estruturas de proteção contra capotamento (EPCC) de t ratores agrícolas. Foi feita uma proposta de design de uma cabina para t ratores estreitos e a parti r dela foi executado o teste vi rtual para a sua validação. A simulação foi fei ta considerando as característ icas não lineares dos materiais, uma vez que a deformação atinge o regime plástico dos mesmos. Como a cabina é uma est rutura soldada relativamente complexa, foram feitas idealizações para se reduzi r o tempo computacional. De posse dos resultados vi rtuais, foi possível prever as regiões mais e menos solici tadas da estrutura sem a necessidade de real izar o teste real, propondo assim alterações de design e de materiais da cabina para tornar a absorção da energia de deformação mais eficiente. / The emphasis of this work is focused on the use of computer simulation within the context of product development. The finite element method was used to simulate the real test that is conducted to validate the st rength and energy absorption capacity of rollover protective st ructures (ROPS) of agricul tural tractors. From a design proposal of a cab to a narrow tractor, the test was performed to validate it . The simulation was made by adopt ing the nonlinear characteristics of the materials, since the deformation reaches the plastic regime. As the cab is a welded structure relatively complex, idealizations were made to reduce the computational time. With the results vi rtual , it was possible to predict the most and least requested regions of the st ructure without the need to run the real test, proposing design and material changes to make the absorption of strain energy more efficiently.

This thesis proposes a novel air flow sensor based on PZT material which is used to measure air velocity in an experimental tunnel or indoor ventilation. The work focuses on designing and verifying the sensor model through finite element analysis (FEA) simulation using COMSOL Multiphysics software. This thesis is devoted to developing a sensor model with a focus on a low-velocity range up to 2 m/s and high sensitivity. The design of the sensor should be robust and reliable for different flow patterns, temperature, and atmospheric pressure variation. The sensor model consists of a fixed cylinder which connects with a bilayer cantilever made of PZT and PDMS material. The laminar flow from the sensor inlet is transformed into the turbulent flow when passing by the fixed cylinder. This structure of bilayer cantilever is designed to generate self-induced oscillation on PZT to overcome the charge leakage over the sensor impedance. Resonance optimization of the sensor structure is investigated to obtain better SNR and performance by adjusting the dimension of the cantilever. From the conducted simulation results, the relationship between the dominant frequency of output voltage generated by PZT and air velocity can be described linearly. In conclusion, it is shown that proposed sensor has a sensitivity of 0.1 m/s and a range of 0.2 to 2 m/s.

A novel insulating cross-arm (ICA) has been developed for new and existing overhead transmission lines of up to 400 kV. The cross-arm consists of four insulating members, end fittings, field grading devices and a nose connection for the attachment of the conductor. The two main structural elements of the assembly have a unique non-cylindrical geometry which gives them improved mechanical characteristics compared to conventional overhead line insulators. The profile for the compression insulator has been designed. After examining six profile variations, it was determined that the lateral orientation which would give the best performance would be with the flat face of the core facing upwards and tilted by 6o. Using the results obtained from performing flashover tests on a conventional 145 kV insulator, the elevation angle for the compression insulator was set to 6o. The dimensions of the compression insulator were calculated based on the assumption that the ICA would be used to uprate an OHL with L3 towers from 275 kV to 400 kV. The optimal insulator profile was determined to be an alternating profile with three different shed sizes, an arcing distance of 3083 mm and a creepage distance of 12470 mm. Electric field grading devices for the ICA were designed. For the LV end, a grading device resembling a ring which follows the general shape of the cross-section of the insulator was designed. For the HV end, an iterative process yielded two designs. First, the ‘butterfly’ grading device was a unibody piece of cast aluminium for all four ICA members. FEA simulations and tests in the laboratory showed that it could effectively control the electric field at voltages of up to 132 kV. The design was patented and the device was used on six cross-arms installed on a live line in Scotland in August 2013. Second, the ‘M-W’ grading device, was a solution made out of four components for managing the field at voltages of up to 400 kV. The device was designed to be easy to install and service, easy and cheap to manufacture and to have minimal visual impact. The compression insulator and the cross-arm assembly were subjected to a multitude of tests adapted from international standards and the Technical Specifications of National Grid. The performed tests aimed to test the electrical characteristics of the cross-arm and the quality of the materials and manufacturing process of the compression insulator. All of the tests were completed successfully except from the corona extinction test for which the appropriate equipment was not available at the time. Two trials were commissioned to examine how the cross-arm performs in a service-like environment. The snow and ice accretion patterns recorded at the mechanical trial site were used for optimising the profile of the compression insulator. The results after a year of continuous monitoring of leakage current and weather conditions at the live trial site showed that there were humidity and visibility thresholds, above 93% for the former and below 400 m for the latter, which increased the average leakage current by 15% on the tension insulators and by 20% on the compression insulators. It was found that when the longitudinal axis of the cross-arm was perpendicular to the weather the leakage current was higher because more of its surface was exposed. The performance of the novel compression insulators was found to be as good as that of the industry standard tension insulators, reaffirming the potency of the design. Finally, on-site observations showed that the ‘butterfly’ grading device could not effectively manage the electric field on the cross-arm at 400 kV, confirming the results of the FEA simulations and testing.

The present research focuses on analyzing the possibility of implementing three dimensional woven composite (3DWC) materials in hip implants. The integration of 3DWCs in hip implants has the possibility to both extend the life-time and improve patient outcomes; by spatially varying mechanical properties to meet both biological needs as well as required mechanical loading. In this study, the bulk material properties of 3DWCs were varied based on woven composite architecture and determined using physics based models, which reflect the realistic geometries of fibers in compaction and preform. The multi-digital chain method combined with Extended Finite Elemental Analysis (XFEA) are adopted in this micro-analysis for composite design. Four different woven architectures with a combination of different existing biocompatible fiber and resins are considered in this study. The main objective is to assess the mechanical response of these biocompatible materials in the design of 3D woven architectures and determine their ability to match the required modulus at different regions of a hip implant. Results obtained show 3DWCs are viable candidates for this application. Multiple architectures and materials chosen, were able to achieve the desired mechanical response. Additional studies can use these results as a starting point and framework for further mechanical and biological testing.

No description available.

<div>Due to reduced pain, shortened hospital stay and recovery, minimally invasive surgery (MIS) is becoming more and more popular in healthcare systems. MIS requires some devices for the motion and force transformation from outside to the inside of the body of a patient, and the strangled cables play a significant role in developing the instrumentations to serve for such purposes. However, current design and selection of a strangled cable is mostly intuitive that depend greatly on designers’ experiences and availability of experimental data, which leads to non-optimized designs and longer design cycles. In this thesis, both of analytical modelling and numerical simulation are proposed to build the relation of applied torque and deflection of part, so that a strangled cable with a given configuration can be characterized in term of its load-deflection relation. The defined relation has its great significance and application potential in the design optimization and precise controls of medical devices for MISs.Besides the various patterns of strangled cables, a Helical hollow strand (HHS®) tube is a special type of strangled cables with single- or multiple- layer configurations., In each layer, each of the helical wires touches its two neighboring helical wires, and it has a coreless hollow at the center. Its primary application is to carry a torsional load in a twisting mode. As an extreme, there is a possibility that all helical wires touch each other, and this forms a statically indeterminate contact obstacle in design analysis. Numerical simulation would predict that contacts occur simultaneously at all possible contacting points under the circumference that the strand is fixed at one end against rotation. In addition, the friction at contacts will affect the torsional deformation; therefore, these contacts must be taken into consideration in the development of analytical and numerical simulation models.This thesis reports the results of the investigation on the characteristics of Helical hollow strand tube (HHS®), more specifically, the relation of torsional deflection and the applied torque over a tube in the clockwise (CW) direction. The numerical simulation approach to predict the torsional deflection of HHS with various design parameters and configurations is emphasized. </div><div><br></div>

Indiana University-Purdue University Indianapolis (IUPUI) / Additively manufactured (AM) metals have been increasingly fabricated for structural applications. However, a major hurdle preventing their extensive application is lack of understanding of their mechanical properties. To address this issue, the objective of this research is to develop a computational model to simulate the creep behavior of nickel alloy 718 manufactured using the laser powder bed fusion (L-PBF) additive manufacturing process. A finite element (FE) model with a subroutine is created for simulating the creep mechanism for 3D printed nickel alloy 718 components. A continuum damage mechanics (CDM) approach is employed by implementing a user defined subroutine formulated to accurately capture the creep mechanisms. Using a calibration code, the material constants are determined. The secondary creep and damage constants are derived using the parameter fitting on the experimental data found in literature. The developed FE model is capable to predict the creep deformation, damage evolution, and creep-rupture life. Creep damage and rupture is simulated as defined by the CDM theory. The predicted results from the CDM model compare well with experimental data, which are collected from literature for L-PBF manufactured nickel alloy 718 of creep deformation and creep rupture, at different levels of temperature and stress. Using the multi-regime Liu-Murakami (L-M) and Kachanov-Rabotnov (K-R) isotropic creep damage formulation, creep deformation and rupture tests of both the secondary and tertiary creep behaviors are modeled. A single element FE model is used to validate the model constants. The model shows good agreement with the traditionally wrought manufactured 316 stainless steel and nickel alloy 718 experimental data collected from the literature. Moreover, a full-scale axisymmetric FE model is used to simulate the creep test and the capacity of the model to predict necking, creep damage, and creep-rupture life for L-PBF manufactured nickel alloy 718. The model predictions are then compared to the experimental creep data, with satisfactory agreement. In summary, the model developed in this work can reliably predict the creep behavior for 3D printed metals under uniaxial tensile and high temperature conditions.