Gary E. Georgeson

The Application of X-Ray Computed Tomography to Materials Development

As aerospace components become more complex, their cost increases and nondestructive evaluation of their quality takes on new significance. X-ray computed tomography is a nondestructive evaluation technique that provides quantitative information on material density, constituents, and dimensions. This capability is of considerable economic value to the aerospace manufacturing community, because it allows better control of materials, processes, and product quality. Additionally, data obtained through computed tomography can be used in the modeling of component behavior to help determine whether defects and flaws are grounds for rejection of a part.

X-Ray Computed Tomography for Geometry Acquisition

X-ray computed tomography (CT) uses penetrating radiation measurements from many angles about an object to reconstruct cross sectional images of the object interior [1–2]. The images are two dimensional maps of the X-ray linear attenuation coefficient for small volume elements in the object defined by the effective X-ray beam size. The CT images provide quantitative measures of component feature dimensions and density as related to the linear X-ray attenuation of the material under study.

X-Ray Computed Tomography for Casting Development

Abstract : Computed tomography (CT) has been used to evaluate specific sand casting product examples for technical and economic benefits. The representative results are applicable to other casting technologies as well. CT has been shown to be cost effective in the development of new castings. The areas which would benefit include internal dimensional measurements (eliminating destructive sectioning), specific region inspections, flaw characterization in critical regions (to allow passing or informed repair of castings), and geometric acquisition for CAD/CAM. The quantitative capability of CT allows an engineering evaluation of castings based upon a correlation with performance. This quantitative measurement capability has also been used to measure the benefit of hot isostatic pressing in casting production. CT is also cost effective for engineering design and analysis by providing rapid geometry acquisition for input to computer aided design systems. This is particularly beneficial for components that do not have existing drawings or cannot be adequately defined until they are made for any reason. Presently CT can serve as an engineering aid to casting manufacturing. In order for CT evaluation to become routine in foundry applications, however, casting designers need to call it out as a measurement technique in the original casting design drawings, specifications on the application of CT must be written, contracts must include CT evaluation as a means for accepting casting quality, and lower cost CT systems must be available.... Computed Tomography (CT), Dimensional measurement, Investment casting, Sand casting, porosity, CAD/CAM, Geometry acquisition, Performance prediction, Material allowables.

X-Ray Computed Tomography for Advanced Materials and Processes.

Abstract : Due to demanding requirements imposed on current and future high- performance aerospace structures, advanced materials are being developed for and used in a variety of aircraft/aerospace applications. Production costs for advanced materials are generally higher and the payback will be greater for data leading to faster decision making or improvement in the product. The development and qualification of new materials, joining and manufacturing processes for advanced aircraft/aerospace applications is accelerated by the availability of quantifiable data on design characteristics and their variations. X-ray computed tomography (CT) provides quantitative measurements of material characteristics in terms of the dimensions, density and composition. The sensitivity of CT is dependent upon a number of factors including the test article and the CT system technology employed. The evaluation capability of CT overcomes the limitation o current qualitative inspection techniques to provide an objective measure of material or component condition. The results of studies involving CT testing of various advanced materials, manufacturing processes and joining methods revealed four specific areas in which there is potential for significant economic benefit from CT. These areas are new product development, process control, noninvasive micrography, and material performance prediction.... Computed Tomography (CT), Advanced materials, Composites, Ceramics Metal Matrix Composite (MMC), Ceramic Matrix Composite (CMC), Superplastic Forming (SPF), Process development, Noninvasive micrography.

X-Ray Computed Tomography for Casting Demonstration

Abstract : Computed tomography (CT) has been applied to cast products demonstrating benefits to product development, dimensional measurements and critical region evaluation. The CTAD program has produced data in a number of reports demonstrating the quantitative measurement capability of CT and its advantages for castings. CT is a measurement tool which can enable greater use of casting by assuring quality in complex structural applications. CT allows an engineering evaluation of castings for a number of criteria such as internal defects, porosity content, three-dimensional location of features and, internal and external dimensions. As casting complexity and part value increases, the application of CT increases in cost effectiveness relative to other technologies. For critical regions of a casting, CT can be superior to radiography for detail sensitivity and relatively inexpensive. Educational material is needed to aid engineers in understanding the applicability and benefits of CT to their problems. Example stories have been used by the CTAD program to demonstrate the areas of CT application and cost benefits. Readers of the case study stories are able to extrapolate from the examples to their problems and evaluate the benefits that CT may provide them.... Computed Tomography (CT), Aluminum, Titanium, Casting, Reinforcement, Economics, Nondestructive evaluation, Flaw characterization.

X-Ray CT for Quantitative Casting Material Evaluation

Casting is an economical way to manufacture parts. However, castings are rarely used as primary structure in aircraft because of the large safety factors that are required for design allowables. This conservatism in utilization is due, in part, to the traditional limitations in evaluation technology for castings. The safety factor increases the overall weight of the casting, which defeats the cost and weight savings that castings offer. Significant gains in casting utilization are possible by a combination of control of the casting microstructure and proper nondestructive evaluation (NDE) of the product. The presently applied NDE criteria for accepting castings involves a comparison to a qualitative standard and has very little to do with their ability to provide operational service. Computed tomography is an enabling technology whose measurements can be used to quantify the product quality level and improve the consistency of casting manufacture.

High Resolution Computed Tomography

Abstract : High resolution (greater than 4 line pairs per millimeter) computed tomography (CT) has been studied for its potential use for engineering evaluation of aerospace components. The CT images provide two dimensional maps of material linear x-ray attenuation coefficients for small volume elements, smaller than 0.001 cubic millimeters. These images are similar to micrographic images of polished surfaces from sectioned components, but are achieved nondestructively. For investigating materials where destructive sectioning relieves stresses, changing the internal configuration of features, such as gaps, high resolution CT provides superior diagnostic information for engineering evaluation. The primary benefits of CT are realized in accelerating schedules through faster data acquisition and reducing engineering risk by providing increased information nondestructively. High resolution CT is particularly well suited to assist in failure analysis investigations. Multiple slice or volume reconstruction high resolution CT can provide full three dimensional models. The cost and performance of high resolution CT systems are functions of the component size and ultimate resolution capability. For many common evaluation needs, the capital cost can be as low as a 50 percent cost add-on to a real-time radiographic imaging system. Relative to micrography, CT can be performed in about on-fifth the time, depending on the number of samples.

Correlation of X-Ray CT Measurements to Shear Strength in Pultruded Composite Materials

Pultrusion is an emerging, economical manufacturing process for composite structures. In a pultrusion system, the composite tapes and fabrics are loaded onto a creel, and the materials are fed into a preform (or shaper), along with any fillers that may be needed. If the fiber is not yet preimpregnated with resin, it is run through a resin bath or resin is injected into the die the material is about to enter. The composite is pulled through the heated die and then cut from the system to produce either a fully or partially cured product. This handleable part is then placed in an autoclave for final cure. A number of variables go into the pultrusion process, including the type of fibers, the resin matrix material, pull rate and cure temperature. Destructive testing, such as shear testing of small sections, is the normal method for assessing the quality of the pultrusion manufacturing product. During manufacture, this cannot be performed on the actual product to be used but only on near neighbor test coupons. This can be time consuming, costly, and part of the product is destroyed.