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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Development of a Method for Predictively Simulating Penetration of a Low Speed Impactor into a Weak Cohesionless Soil

Arrington, Dusty Ray 03 October 2013 (has links)
Since the horrific attacks on September 11th 2001, the United States government and research community have been focused on how to better protect US assets across the Globe. This push for safety led the research community to develop “F2656-07 Standard Test Method for Vehicle Crash Testing of Perimeter Barriers” in 2007 which standardized the method of validating a perimeter security barrier’s ability to withstand an impact from an attacking vehicle. Many of these security barriers rely on weak cohesionless soils to stop attacking vehicles. Designers currently rely heavily on hand calculations and engineering judgment when sizing these installations. This simplified analysis is generally used because of the complex nature of these soils under impact. These soils could be simulated in advanced finite element simulations; however, traditional modeling techniques will not allow for the simulation of these complex behaviors. Due to the complex nature of these simulations, new modeling techniques need to be evaluated and their use needed to be perfected. From this, a new method for creating a predictive simulation of a low speed impactor into a weak cohesionless soil was generated. This paper presents the development of a method by which a predictive simulation was created using only standard soil tests parameters. This paper also presents measured data from physical impact tests utilized to validate the method by which the simulation was generated. Next, the paper gives a detailed comparison of the results of the physical testing and the simulated impacts. The paper finally gives a summary of where the method is successful and where it needs improvement. The resulting methodology developed in this paper defines a reasonable process for creating a predictive simulation of a rigid impactor penetrating weak cohesionless sands. This finding is validated by a reasonable correlation between the measured and simulated impact penetrations. This paper also highlights the high variability of measured penetrations when testing with these soil materials.
2

Finite Element Analysis Of A Test Specimen For Strength Of A Co-polymer Layer At A Bone-implant Interface

Chhabra, Nitin 01 January 2004 (has links)
The aim of this work is to evaluate the mechanical strength of a co-polymer of 2-hydroxyethylmethacrylate (HEMA) and methylmethacrylate (MMA), so that it can be applied as an interfacial layer between bone cement and steel implants to improve their performance and life. Finite element (FE) analysis techniques are used to assess the behavior of the interface layer under static and dynamic loading conditions. The material property of the co-polymer is a function of its composition and water saturation. The factors affecting the strength of the bone-implant interface are many. Implant interfacial fracture can lead to decreased stability. Fatigue life is a very important process in failure. The results obtained from static and dynamic analyses show that increasing the percentage of HEMA improves the strength of the interface by reducing the stiffness of the implant, absorbing more energy and by reducing the interfacial stress peaks and making the stress distribution more nearly uniform.
3

Comparative assessment of implicit and explicit finite element solution schemes for static and dynamic civilian aircraft seat certification (CS25.561 and CS25.562)

Gulavani, Omkar Vitthal 03 1900 (has links)
Due to the competitive nature of airline industry and the desire to minimise aircraft weight, there is a continual drive to develop lightweight, reliable and more comfortable seating solutions, in particular, a new generation slim economy seat. The key design challenge is to maximise the “living space” for the passenger, with strict adherence to the ‘Crash Safety Regulations’. Cranfield University is addressing the needs of airliners, seat manufactures and safety regulating bodies by designing a completely novel seat structure coined as “Sleep Seat”. A generous angle of recline (40 degree), movement of “Seat Pan” along the gradient, fixed outer shell of the backrest, and a unique single “Forward Beam” design distinguishes “Sleep Seat” form current generation seats. It is an ultra-lightweight design weighing 8kg (typical seat weight is 11kg). It has to sustain the static (CS 25.561) and dynamic (CS25.562) “Emergency landing” loads as specified by “Certification Specifications (CS). Apart from maintaining structural integrity; a seat-structure must not deform, which would impede evacuation, should absorb energy so that the loads transferred to Occupants are within human tolerance limits and should always maintain survivable space around the Occupant. All these parameters, which increase a life-expectancy in a ‘survivable’ crash, can be estimated using either experimental testing or virtual simulation tools such as “Finite Element Analysis (FEA). Design of the “Sleep Seat” is still in its conceptual phase and therefore experimental testing for all the design iterations involved is unrealistic, given a measure of the costs and timescales involved. Therefore focus of research is to develop practical and robust FE methodologies to assess static and dynamic performances of a seat-structure so as to compare different design concepts based on their strength, seat interface loads (a limit defined by strength of aircraft-floor), maximum deformations and cross-sectional forces ... [cont.].
4

Comparative assessment of implicit and explicit finite element solution schemes for static and dynamic civilian aircraft seat certification (CS25.561 and CS25.562)

Gulavani, Omkar Vitthal January 2013 (has links)
Due to the competitive nature of airline industry and the desire to minimise aircraft weight, there is a continual drive to develop lightweight, reliable and more comfortable seating solutions, in particular, a new generation slim economy seat. The key design challenge is to maximise the “living space” for the passenger, with strict adherence to the ‘Crash Safety Regulations’. Cranfield University is addressing the needs of airliners, seat manufactures and safety regulating bodies by designing a completely novel seat structure coined as “Sleep Seat”. A generous angle of recline (40 degree), movement of “Seat Pan” along the gradient, fixed outer shell of the backrest, and a unique single “Forward Beam” design distinguishes “Sleep Seat” form current generation seats. It is an ultra-lightweight design weighing 8kg (typical seat weight is 11kg). It has to sustain the static (CS 25.561) and dynamic (CS25.562) “Emergency landing” loads as specified by “Certification Specifications (CS). Apart from maintaining structural integrity; a seat-structure must not deform, which would impede evacuation, should absorb energy so that the loads transferred to Occupants are within human tolerance limits and should always maintain survivable space around the Occupant. All these parameters, which increase a life-expectancy in a ‘survivable’ crash, can be estimated using either experimental testing or virtual simulation tools such as “Finite Element Analysis (FEA). Design of the “Sleep Seat” is still in its conceptual phase and therefore experimental testing for all the design iterations involved is unrealistic, given a measure of the costs and timescales involved. Therefore focus of research is to develop practical and robust FE methodologies to assess static and dynamic performances of a seat-structure so as to compare different design concepts based on their strength, seat interface loads (a limit defined by strength of aircraft-floor), maximum deformations and cross-sectional forces ... [cont.].
5

Design and Development of an Energy Absorbing Seat and Ballistic Fabric Material Model to Reduce Crew Injury Caused by Acceleration From Mine/IED Blast

Nilakantan, Gaurav 02 October 2006 (has links)
No description available.

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