Unitized aircraft structures have the potential to be more efficient than current aircraft structures. The Electron Beam Freeform Fabrication (EBF3) process can be used to manufacture unitized aircraft structures. The structural efficiency of blade stiffened panels made with EBF3 was compared to panels made by integrally machining from thick plate. The panels were tested under two load cases in a combined compression-shear load test fixture. One load case tested the panels' responses to a higher compressive load than the shear load. The second load case tested the panels' responses to an equal compressive and shear load. Finite element analysis was performed to compare with the experimental results. The EBF3 panels failed at a 18.5% lower buckling load than the machined panels when loaded mostly in compression but at an almost two times higher buckling load than the machined panels when the shear matched the compressive load. The finite element analysis was in good agreement with the experimental results prior to buckling. The results demonstrate that the EBF3 process has the capabilities of manufacturing stiffened panels that behave similarly to machined panels prior to buckling. Once the EBF3 panels buckled, the buckled shape of the EBF3 panels was different from the machined panels, generally buckling in the opposite direction of what was observed with the machined panels. This was also expected based on the finite element analysis. The different post-buckling response between the two manufacturing techniques was attributed to the residual stress and associated distortion induced during the EBF3 manufacturing process. / Master of Science

Rapid prototyping systems have advanced significantly with respect to material capabilities, fabrication speed, and surface quality. However, build jobs are still manually activated one at a time. The result is non-productive machine time whenever an operator is not at hand to make a job changeover. A low-cost auxiliary system, named Continuous Layered Manufacturing (CLM), has been developed to automatically load and unload the FDM 1600 rapid prototyping system (Stratasys, Inc.). The modifications made to the FDM 1600 system are minimal. The door to the FDM 1600 build chamber is removed, and the .SML build files that are used to drive the FDM 1600 are modified at both ends to facilitate synchronized operation between the two systems. The CLM system is capable of running three consecutive build jobs without operator intervention. As long as an operator removes finished build jobs, and adds new build trays before at most every three build jobs, the FDM can operate near indefinitely. The impact of the CLM system on the productivity of the FDM 1600 rapid prototyping system is demonstrated by the expected reduction from the customary eight weeks down to a future three and one-half weeks required to complete the typical forty build jobs during a semester in the course ME 4644 Introduction to Rapid Prototyping at Virginia Tech. / Master of Science

Constrained negative stiffness elements in volume concentrations (1% to 2%) embedded within viscoelastic materials have been shown to provide greater energy absorption than conventional materials [Lakes et al., Nature (London) 410, 565–567 (2001)]. This class of composite materials, called meta-materials, could be utilized in a variety of applications including noise reduction, anechoic coatings and transducer backings. The mechanism underlying the meta-material's behavior relies on the ability of the negative stiffness element to locally deform the viscoelastic material, dissipating energy in the process. The work presented here focuses specifically on the design of the negative stiffness elements, which take the form of buckled beams. By constraining the beam in an unstable, S-shaped configuration, the strain energy density of the beam will be at a maximum and the beam will accordingly display negative stiffness. To date, physical realization of these structures has been limited due to geometries that are difficult to construct and refine with conventional manufacturing materials and methods. By utilizing the geometric freedoms allowed by the Selective Laser Sintering (SLS) machines, these structures can be built and tuned for specific dynamic properties. The objective of this research was to investigate the dynamic behavior of SLS-constructed meso-scale negative stiffness elements with the future intention of miniaturizing the elements to create highly absorptive meta-materials. This objective was accomplished first through the development and analysis of a mathematical model of the buckled beam system. A characterization of the Nylon 11 material was performed to obtain the material properties for the parts that were created using SLS. Applying the mathematical model and material properties, a tuned meso-scale negative stiffness structure was fabricated. Transmissibility tests of the meso-scale structure revealed that the constrained negative stiffness system was able to achieve overall higher damping and vibration isolation than an unconstrained system. Quasistatic behavior of the system indicated that these elements would be ideal for implementation within meta-materials. Based on the results of the meso-scale system, a method to test a representative volume element for a negative stiffness meta-material was developed for future completion. / text

The goal of this dissertation is to develop a model relating LENSâ„¢ process parameters to deposited thickness, incorporating the effect of substrate heating. A design review was carried out, adapting the technique of functional decomposition borrowed from axiomatic design. The review revealed that coupling between the laser path and laser power caused substrate heating. The material delivery mechanism was modeled and verified using experimental data. It was used in the derivation of the average deposition model which predicted deposition based on build parameters, but did not incorporate substrate heating. The average deposition model appeared capable of predicting deposited thickness for single line, 1- layer and 2-layer builds, performing best for the 1- layer builds which were built under essentially isothermal conditions. This model was extended to incorporate the effect of substrate heating, estimated using an energy partition approach. The energy used for substrate heating was modeled as a series of timed heating events from an instantaneous point heat source along the path of the laser. The result was called the spatial deposition model, and was verified using the same set of experimental data. The model appeared capable of predicting deposited thickness for single line, 1- layer and 2- layer builds and was able to predict the characteristic temperature rise near the borders as the laser reversed direction.

This dissertation presents information gathered and analyzed through an electronic internet-based Delphi Survey process. The purpose of this study is to identify a consensus of factors that might forecast the future effects of Rapid Prototyping (RP) technology on engineering design education when used for the purpose of overcoming the limitations of 2D representation of 3D space. The identification of consensus was developed from the collection of opinions from a panel of experts in RP technology. Early adopters of emerging technologies can reduce risk through careful research, but decisions must often be made before significant quantitative data are available. Expert subjective judgment may be a valuable source of information for making decisions. RP is just one of the tools used in engineering design education for visualization. This research should help to guide faculty members in making decisions regarding the use of RP technology in the curriculum. The one consensus reached by the panel is that 3D CAD will replace 2D CAD as the default modeling tool in most product-design related curricula within 5 years. The general conclusion of the study is that the appropriate use of the technology in the curriculum is largely situational.

The focus of this dissertation is on the development of a solid freeform fabrication (SFF) process for the design and manufacture of porous biodegradable orthopaedic implants from calcium polyphosphate (CPP). Porous CPP structures are used as bone substitutes for regenerating bone defects and/or as substrates in formation of so-called “biphasic” implants for repair of damaged osteochondral tissues. The CPP implants can be utilized in the treatment of many musculoskeletal diseases, osteochondral defects, and bone tumours while replacement of the defect site is required. In this study, the fabrication of CPP structures was developed through a powder-based SFF technique known as adhesive bonding 3D-printing. SFF is an advanced alternative to the “conventional” fabrication method consisting of gravity sintering of CPP pre-forms followed by machining to final form, as SFF enables rapid manufacturing of complex-shaped bio-structures with controlled internal architecture. To address the physical and structural properties of the porous SFF-made components, they were characterized using scanning electron microscopy, micro-CT scanning and mercury intrusion porosimetry. Specific surface area and permeability of the porous structures were also determined. Additionally, the chemical properties (crystallinity) of the specimens were identified by X-ray diffraction. The mechanical properties of the crystalline CPP material were also measured by micro- and nano-indentation. Moreover, the porous structures were tested by uniaxial and diametral mechanical compression to determine the compressive and tensile strengths, respectively. Furthermore, the effect of the stacked-layer orientation on the mechanical properties of the SFF-made constructs was investigated through the production of samples with horizontal or vertical stacked-layers. The properties of the SFF-made samples were compared with those of the conventionally-made CPP constructs. The SFF-made implants showed drastically higher compressive mechanical strength compared to the conventionally-formed samples with identical porosity. It was also shown that the orientation of the stacked-layer has substantial influence on the mechanical strengths. Moreover, this thesis examined the ability of in vitro forming of cartilaginous tissue on the SFF-made substrates where the chondrocytes cellular response to the CPP implants was evaluated histologically and biochemically. In addition, an initial in vivo assessment of the CPP structures as bone substitutes was conducted using a rabbit medial femoral site model. Significant amount of new-bone was formed within the CPP porous constructs during the 6-week implantation period demonstrating appropriate biological response of SFF-made CPP structures for bone substitute applications. Another accomplishment of this thesis was the development of a mathematical model which predicts the compact density of powder layers spread by a counter-rotating roller in the SFF technique. The results may be used in the control of the apparent density of the final implant. The potential of the developed SFF method as an efficient and reproducible technique for the production of porous CPP structures for use in orthopaedics and musculoskeletal tissue regenerative applications was concluded.

Rapid prototyping (RP) is a set of fabrication technologies that are used to produce accurate parts directly from computer aided drawing (CAD) data. These technologies are unique in a way that they use an additive fabrication approach in which a three dimensional (3D) object is directly produced. In this thesis study, a RP application with a modular architecture is designed and implemented to satisfy the possible requirements of future rapid prototyping studies. After a functional classification, the developed RP software is divided into View, RP and Slice Modules. In the RP module, the process parameter selection and optimal build orientation determination steps are carried out. In the Slice Module, slicing and tool path generation steps are performed. View Module is used to visualize the inputs and outputs of the RP software. To provide 3D visualization support for View Module, a fully independent, open for development, high level 3D modeling environment and graphics library called Graphics Framework is developed. The resulting RP application is benchmarked with the RP software packages in the market according to their memory usage and process time. As a result of this benchmark, it is observed that the developed RP software has presented an equivalent performance with the other commercial RP applications and has proved its success.

The focus of this dissertation is on the development of a solid freeform fabrication (SFF) process for the design and manufacture of porous biodegradable orthopaedic implants from calcium polyphosphate (CPP). Porous CPP structures are used as bone substitutes for regenerating bone defects and/or as substrates in formation of so-called “biphasic” implants for repair of damaged osteochondral tissues. The CPP implants can be utilized in the treatment of many musculoskeletal diseases, osteochondral defects, and bone tumours while replacement of the defect site is required. In this study, the fabrication of CPP structures was developed through a powder-based SFF technique known as adhesive bonding 3D-printing. SFF is an advanced alternative to the “conventional” fabrication method consisting of gravity sintering of CPP pre-forms followed by machining to final form, as SFF enables rapid manufacturing of complex-shaped bio-structures with controlled internal architecture. To address the physical and structural properties of the porous SFF-made components, they were characterized using scanning electron microscopy, micro-CT scanning and mercury intrusion porosimetry. Specific surface area and permeability of the porous structures were also determined. Additionally, the chemical properties (crystallinity) of the specimens were identified by X-ray diffraction. The mechanical properties of the crystalline CPP material were also measured by micro- and nano-indentation. Moreover, the porous structures were tested by uniaxial and diametral mechanical compression to determine the compressive and tensile strengths, respectively. Furthermore, the effect of the stacked-layer orientation on the mechanical properties of the SFF-made constructs was investigated through the production of samples with horizontal or vertical stacked-layers. The properties of the SFF-made samples were compared with those of the conventionally-made CPP constructs. The SFF-made implants showed drastically higher compressive mechanical strength compared to the conventionally-formed samples with identical porosity. It was also shown that the orientation of the stacked-layer has substantial influence on the mechanical strengths. Moreover, this thesis examined the ability of in vitro forming of cartilaginous tissue on the SFF-made substrates where the chondrocytes cellular response to the CPP implants was evaluated histologically and biochemically. In addition, an initial in vivo assessment of the CPP structures as bone substitutes was conducted using a rabbit medial femoral site model. Significant amount of new-bone was formed within the CPP porous constructs during the 6-week implantation period demonstrating appropriate biological response of SFF-made CPP structures for bone substitute applications. Another accomplishment of this thesis was the development of a mathematical model which predicts the compact density of powder layers spread by a counter-rotating roller in the SFF technique. The results may be used in the control of the apparent density of the final implant. The potential of the developed SFF method as an efficient and reproducible technique for the production of porous CPP structures for use in orthopaedics and musculoskeletal tissue regenerative applications was concluded.

Thesis (M. Tech.) -- Central University of Technology, Free State, 2008 / As the tendency to use sol id freeform fabrication (SFF) technology for the manufacture of end use parts grew, so too did the need for a set of general guidelines that would aid designers with designs aimed specifically for rapid manufacture. Unfortunately, the revolutionary additive nature of SFF technology left certain fundamental principles of conventional design for manufacture and assembly outdated. This implied that whole chapters of theoretical work that had previously been done in this field had to be revised before it could be applied to rapid manufacturing. Furthermore, this additive nature of SFF technology seeded a series of new possibilities and new advantages that could be exploited in the manufacturing domain, and as a result drove design for rapid manufacturing principles even further apart from conventional design for manufacture and assembly philosophy. In this study the impact that rapid manufacture had on the conventional product development process and conventional design for manufacture and assembly guidelines were investigated. This investigation brought to light the inherent strengths and weaknesses of SFF, as well as the design for manufacture and assembly guidelines that became invalid, and consequently lead directly to the characterization of a set of design for rapid manufacture guidelines.

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