REU Projects for Summer 2007
The following are summaries of the research projects conducted during the 2007 Metrology REU, adapted from submissions by REU participants.
A Study of Best Fitting Practices using AFI Generated CAD Models of Basic Shapes
Accordion Fringe Interferometry (AFI) is a new technology being explored in the area of non-contact coordinate measuring. Because the AFI is very new, there has not been much research on standardizing scanning and data fitting procedures for basic shapes. The position of an object during scanning, exposure time of the camera used, reflectivity of the object’s material, sequence of fitting scans and number of scans incorporated into the data fitting process all play an important role in the accuracy of the data collected and the quality of the final CAD model. If the AFI is eventually going to be used for quality control in Industry, it is important to understand how to acquire the most accurate data and how to precisely fit the data together, starting with basic shapes.
This project explores the optimum fitting practices of a triangular prism and an elliptic cylinder. Aspects studied include shape of object being scanned, types of scans used in reference to angle of shape during scanning, number of scans fit together, sequence of scans fit together, capabilities of Polyworks’ best fit option and ultimately the accuracy of the AFI.
Study of Friction, Wear and Characterization during Flat Lapping of 304 Stainless Steel and 1018 Steel
In this research, 1018 Steel and 304 Stainless Steel were examined under a scanning electron microscope (SEM) before and after lapping. The elemental composition change was determined by the Energy-dispersive X-ray spectroscopy (EDS). Increased aluminum and silicon concentrations were found among the metal samples that were lapped with aluminum oxide and silicon carbide abrasives, respectively. Also, the friction and wear models were revised under the new assumption that the abrasive geometry was an ellipse. With this assumption, the coefficients of friction for 1018 Steel and 304 Stainless were successfully found.
Method for Measuring Freeform Objects Using Accordion Fringe Interferometry
Accordion Fringe Interferometry (AFI) is a new development in coordinate metrology. Because this technology is innovative, little has been published on how to optimally use its capabilities. There exists no published general method on how to use the AFI machine’s speed and accuracy to efficiently acquire the coordinates of freeform shapes. The goal of this experiment was to develop a general method for obtaining data for freeform surfaces since this problem’s solution is essential to the development of AFI technology. The AFI machine used in this experiment was an AFI 5000P system from Dimensional Photonics, and the software used was PolyWorks.
Since each freeform shape can be unique and complex, the experiment first focused on planar and cylindrical surfaces. These were individually examined at different orientations to find the positions that provided the most surface points in one shot and gave sufficient data to represent the surface evenly. This data was applied in determining a general method for gathering areas of data and then ultimately stitching multiple images together.
In the proposed general method, the divisions of an object would be determined by the angles of the points’ tangent planes so the least number of shots would have to be taken. Fabric dots were positioned strategically on the overlap areas so the shots could be stitched using PolyWorks. The effects of stitching were touched upon briefly. The proposed method was shown to work on a half-cylinder piece and a skull model, as the objects were captured sufficiently for all surfaces and in a minimal number of shots.
3D Microfabrication Using DLP Technology in Manufacturing
Three-dimensional mask-projection micro stereolithography is an emerging technology in the field of microfabrication. It uses a light source to harden a photosensitive polymer into a desired shape on a micron scale. The process provides fast production times for applications such as rapid prototyping and micro electromechanical systems (MEMS), allowing an easier method for producing fine mechanical elements for use in compact electronic devices. It also provides a new avenue for living tissue research, where hydrophilic scaffolds are built to create a sustainable environment for tissue cells.
The focus of this research project is to design and construct 3-dimensional tissue scaffolds by layered mask projection micro-stereolithography in a photosensitive polymer solution. The system is comprised of a UV light source, a digital micromirror device (DMD), a series of lenses and filters, and a container of liquid polymer and photoinitiator. An ultraviolet light generator projects a concentrated light beam through a lens and filter to collimate it, ensuring uniformity of the UV rays. The UV light is reflected off of the DMD and focused through a lens into the liquid polymer. A computer feeds a user-defined image to the DMD, which acts as a dynamic mask to selectively reflect light onto the sample. The sample solution resin reacts with the light on contact and solidifies in the regions illuminated by the DMD.
To produce truly 3-dimensional microstructures, it is necessary to expose multiple layers of polymer on top of each other. In order to do so, the sample must be lowered the distance of at least one layer thickness between exposures. In this manner, a 3D sample is built from the bottom up.
Damage Detection in SHM Applications with Special Empasis on Highway Bridges
Damage detection is a goal this is strived for by all Structural Health Monitoring (SHM) systems. Knowing the origin of damage on structures depended upon by many populations allows for the preservation of the structure’s integrity or, at the very least, extensive knowledge of the lifespan left in that particular structure. Our research focuses on damage detection specific to highway bridges in two ways. The first methodology is through the measurement of strains to calculate stress. Knowing how the stresses are acting on a particular bridge is critical to damage detection. However, there is no physical instrument that can measure stress; as such, an intermediate step must be carried out. The intermediate step in the case is the calculation of the principal strains. This is accomplished with the use of strain rosettes, which measure the directionality as well as the magnitude of the strains. The next step is to then convert these values to stresses, using multiple mathematical relationships and transformations. There are different types of stresses that act on structures; ultimately, this research is focused on finding the principal stresses on highway bridges. Principal stresses are calculated from the normal stress (acting vertically downwards) as well as the shear stress (acting along the structure), and are an excellent representation of the overall stress acting on a structure. Upon calculation of the principal stresses, the final step is to use the technique of triangulation to pinpoint exactly where the damage on the bridge in question occurred. Experiments were carried out on an I-Girder from a highway bridge. A single strain rosette, along with two linear strain gauges, was placed on the Girder to take data when the loads were applied.
As a secondary quantifier for damage detection, the modal frequencies of the I-Girder were measured using accelerometers. When a structure undergoes damage, its stiffness and natural frequency both change. The accelerometer measures this change in the time domain; the Fourier Transform can convert this data to the frequency domain. Ultimately, this part of the research was thoroughly secondary, and was used primarily as another way to check that the strain rosette was correctly monitoring the damage on the girder.
Characterization of Flat Lapped Metals using Scanning Electron Microscopy
In this paper, the objective is to characterize flat lapped metals and also to determine if chemical reactions could happen between surface of metals and abrasives. Two samples of Aluminum 2024 and 1018 steel are used in the experiment. One sample is lapped with garnet as the abrasive and the other is lapped with white aluminum oxide. Each abrasive is mixed with water to produce slurry.
Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) are used for the analysis of sample surfaces. A Profilometer is also used for characterization of metals. SEM is used to get images of surfaces before and after lapping. EDS is used to determine elements present on the surfaces. These two are used before and after lapping and results are compared. These two instruments are also used to determine the characteristics of metals after lapping.
The results indicate that some kind of activity is occurring on the surfaces but determining what kind of activity is a difficult task. A theory is proposed for chemical reactions that may happen between the surface of metal and abrasive. This theory is then investigated based on results from SEM and EDS. One of the explanations presented is that the abrasives become embedded into the grain boundaries and only oxidation can occur.
The following are summaries of the research projects conducted during the 2007 Metrology REU, adapted from submissions by REU participants.
A Study of Best Fitting Practices using AFI Generated CAD Models of Basic Shapes
Accordion Fringe Interferometry (AFI) is a new technology being explored in the area of non-contact coordinate measuring. Because the AFI is very new, there has not been much research on standardizing scanning and data fitting procedures for basic shapes. The position of an object during scanning, exposure time of the camera used, reflectivity of the object’s material, sequence of fitting scans and number of scans incorporated into the data fitting process all play an important role in the accuracy of the data collected and the quality of the final CAD model. If the AFI is eventually going to be used for quality control in Industry, it is important to understand how to acquire the most accurate data and how to precisely fit the data together, starting with basic shapes.
This project explores the optimum fitting practices of a triangular prism and an elliptic cylinder. Aspects studied include shape of object being scanned, types of scans used in reference to angle of shape during scanning, number of scans fit together, sequence of scans fit together, capabilities of Polyworks’ best fit option and ultimately the accuracy of the AFI.
Study of Friction, Wear and Characterization during Flat Lapping of 304 Stainless Steel and 1018 Steel
In this research, 1018 Steel and 304 Stainless Steel were examined under a scanning electron microscope (SEM) before and after lapping. The elemental composition change was determined by the Energy-dispersive X-ray spectroscopy (EDS). Increased aluminum and silicon concentrations were found among the metal samples that were lapped with aluminum oxide and silicon carbide abrasives, respectively. Also, the friction and wear models were revised under the new assumption that the abrasive geometry was an ellipse. With this assumption, the coefficients of friction for 1018 Steel and 304 Stainless were successfully found.
Method for Measuring Freeform Objects Using Accordion Fringe Interferometry
Accordion Fringe Interferometry (AFI) is a new development in coordinate metrology. Because this technology is innovative, little has been published on how to optimally use its capabilities. There exists no published general method on how to use the AFI machine’s speed and accuracy to efficiently acquire the coordinates of freeform shapes. The goal of this experiment was to develop a general method for obtaining data for freeform surfaces since this problem’s solution is essential to the development of AFI technology. The AFI machine used in this experiment was an AFI 5000P system from Dimensional Photonics, and the software used was PolyWorks.
Since each freeform shape can be unique and complex, the experiment first focused on planar and cylindrical surfaces. These were individually examined at different orientations to find the positions that provided the most surface points in one shot and gave sufficient data to represent the surface evenly. This data was applied in determining a general method for gathering areas of data and then ultimately stitching multiple images together.
In the proposed general method, the divisions of an object would be determined by the angles of the points’ tangent planes so the least number of shots would have to be taken. Fabric dots were positioned strategically on the overlap areas so the shots could be stitched using PolyWorks. The effects of stitching were touched upon briefly. The proposed method was shown to work on a half-cylinder piece and a skull model, as the objects were captured sufficiently for all surfaces and in a minimal number of shots.
3D Microfabrication Using DLP Technology in Manufacturing
Three-dimensional mask-projection micro stereolithography is an emerging technology in the field of microfabrication. It uses a light source to harden a photosensitive polymer into a desired shape on a micron scale. The process provides fast production times for applications such as rapid prototyping and micro electromechanical systems (MEMS), allowing an easier method for producing fine mechanical elements for use in compact electronic devices. It also provides a new avenue for living tissue research, where hydrophilic scaffolds are built to create a sustainable environment for tissue cells.
The focus of this research project is to design and construct 3-dimensional tissue scaffolds by layered mask projection micro-stereolithography in a photosensitive polymer solution. The system is comprised of a UV light source, a digital micromirror device (DMD), a series of lenses and filters, and a container of liquid polymer and photoinitiator. An ultraviolet light generator projects a concentrated light beam through a lens and filter to collimate it, ensuring uniformity of the UV rays. The UV light is reflected off of the DMD and focused through a lens into the liquid polymer. A computer feeds a user-defined image to the DMD, which acts as a dynamic mask to selectively reflect light onto the sample. The sample solution resin reacts with the light on contact and solidifies in the regions illuminated by the DMD.
To produce truly 3-dimensional microstructures, it is necessary to expose multiple layers of polymer on top of each other. In order to do so, the sample must be lowered the distance of at least one layer thickness between exposures. In this manner, a 3D sample is built from the bottom up.
Damage Detection in SHM Applications with Special Empasis on Highway Bridges
Damage detection is a goal this is strived for by all Structural Health Monitoring (SHM) systems. Knowing the origin of damage on structures depended upon by many populations allows for the preservation of the structure’s integrity or, at the very least, extensive knowledge of the lifespan left in that particular structure. Our research focuses on damage detection specific to highway bridges in two ways. The first methodology is through the measurement of strains to calculate stress. Knowing how the stresses are acting on a particular bridge is critical to damage detection. However, there is no physical instrument that can measure stress; as such, an intermediate step must be carried out. The intermediate step in the case is the calculation of the principal strains. This is accomplished with the use of strain rosettes, which measure the directionality as well as the magnitude of the strains. The next step is to then convert these values to stresses, using multiple mathematical relationships and transformations. There are different types of stresses that act on structures; ultimately, this research is focused on finding the principal stresses on highway bridges. Principal stresses are calculated from the normal stress (acting vertically downwards) as well as the shear stress (acting along the structure), and are an excellent representation of the overall stress acting on a structure. Upon calculation of the principal stresses, the final step is to use the technique of triangulation to pinpoint exactly where the damage on the bridge in question occurred. Experiments were carried out on an I-Girder from a highway bridge. A single strain rosette, along with two linear strain gauges, was placed on the Girder to take data when the loads were applied.
As a secondary quantifier for damage detection, the modal frequencies of the I-Girder were measured using accelerometers. When a structure undergoes damage, its stiffness and natural frequency both change. The accelerometer measures this change in the time domain; the Fourier Transform can convert this data to the frequency domain. Ultimately, this part of the research was thoroughly secondary, and was used primarily as another way to check that the strain rosette was correctly monitoring the damage on the girder.
Characterization of Flat Lapped Metals using Scanning Electron Microscopy
In this paper, the objective is to characterize flat lapped metals and also to determine if chemical reactions could happen between surface of metals and abrasives. Two samples of Aluminum 2024 and 1018 steel are used in the experiment. One sample is lapped with garnet as the abrasive and the other is lapped with white aluminum oxide. Each abrasive is mixed with water to produce slurry.
Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) are used for the analysis of sample surfaces. A Profilometer is also used for characterization of metals. SEM is used to get images of surfaces before and after lapping. EDS is used to determine elements present on the surfaces. These two are used before and after lapping and results are compared. These two instruments are also used to determine the characteristics of metals after lapping.
The results indicate that some kind of activity is occurring on the surfaces but determining what kind of activity is a difficult task. A theory is proposed for chemical reactions that may happen between the surface of metal and abrasive. This theory is then investigated based on results from SEM and EDS. One of the explanations presented is that the abrasives become embedded into the grain boundaries and only oxidation can occur.
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