In the chemical transport field, such as petro-chemicals or food processing, there is a need to quantify the spatially varying temperature and phase state of the material within a cylindrical vessel, such as a pipeline, using non-invasive techniques. Using ultrasonic signals, which vary in time-of-flight, intensity, and wave characteristics based on the temperature and phase of a material, an automated technique is presented which can provide a non-axisymmetric map of the phase and temperature inside a cylindrical vessel within a single plane using exclusively information from the through-transmission wave and the external temperature profile. This research demonstrates the approach using an amorphous wax, due to its stable nature and ability to be reheated many times without changing the properties of the wax. Due to its amorphous nature, the wax transitions from a solid to a low-viscosity fluid over a range of temperatures. This behavior is similar to that of a thermoplastic and a slurry experiencing curing. As the spatial temperature within a container of wax increases the time of flight for an ultrasonic signal will change. Results presented indicate the ability of the investigated technique to map the temperature and phase change of the wax based solely on the ultrasonic signals and knowledge of the external temperature on the outer edge of the vessel.
Additively manufactured (AM) components often exhibit significant discontinuities and indications without a clear understanding of how they might affect the mechanical properties of a part during qualification and service. This uncertainty is unacceptable for the design and manufacturing of most aerospace components. Current research in both mechanical testing and nondestructive evaluation involves developing methods for characterizing and inspecting AM components as the use of such materials continues to rise. Although several AM manufacturing methods have been developed in recent decades, this paper focuses on AM production-ready processes for a direct metal laser sintering (DMLS) powder bed fusion machine and will provide background on Sandia National Laboratories' research efforts in this area. Tensile bar samples manufactured using the DMLS powder bed fusion method were inspected in this study, and the results of ultrasonic spectroscopy for assessing internal flaws will be presented. A combination of material property evaluation, microstructural characterization, and nondestructive inspection techniques will also be described. The results obtained from these material evaluation methods assist in determining inspection limits and methods for qualifying AM materials.
Measures of energy input and spatial energy distribution during laser powder bed fusion additive manufacturing have significant implications for the build quality of parts, specifically relating to formation of internal defects during processing. In this study, scanning electron microscopy was leveraged to investigate the effects of these distributions on the mechanical performance of parts manufactured using laser powder bed fusion as seen through the fracture surfaces resulting from uniaxial tensile testing. Variation in spatial energy density is shown to manifest in differences in defect morphology and mechanical properties. Computed tomography and scanning electron microscopy inspections revealed significant evidence of porosity acting as failure mechanisms in printed parts. These results establish an improved understanding of the effects of spatial energy distributions in laser powder bed fusion on mechanical performance.
At present, there are many methods to identify the temperature and phase of a material using invasive techniques. However, most current methods require physical contact or implicit methods utilizing light reflectance of the specimen. This work presents a nondestructive inspection method using ultrasonic wave technology that circumvents these disadvantages to identify phase change regions and infer the temperature state of a material. In the present study an experiment is performed to monitor the time of flight within a wax as it undergoes melting and the subsequent cooling. Results presented in this work show a clear relationship between a material's speed of sound and its temperature. The phase change transition of the material is clear from the time of flight results, and in the case of the investigated material, this change in the material state occurs over a range of temperatures. The range of temperatures over which the wax material melts is readily identified by speed of sound represented as a function of material temperature. The melt temperature, obtained acoustically, is validated using Differential Scanning Calorimetry (DSC), which uses shifts in heat flow rates to identify phase transition temperature ranges. The investigated ultrasonic NDE method has direct applications in many industries, including oil and gas, food and beverage, and polymer composites, in addition to many implications for future capabilities of nondestructive inspection of multi-phase materials.
Ultrasound techniques are capable of monitoring changes in the time-of-flight as a material is exposed to different thermal environments. The focus of the present study is to identify the phase of a material via ultrasound compression wave measurements in a through transmission experimental setup as the material is heated from a solid to a liquid and then allowed to re-solidify. The present work seeks to expand upon the authors' previous research, which proved this through transmission phase monitoring technique was possible, by considering different experimental geometries. The relationship between geometry, the measured speed of sound, and the temperature profile is presented. The use of different volumes helps in establishing a baseline understanding of which aspects of the experiment are geometry dependent and which are independent. The present study also investigates the relationship between the heating rate observed in the experiment and the measured speed of sound. The trends identified between the experimental geometry, heat rate and ultrasound wave speed measurement assist in providing a baseline understanding of the applicability of this technique to various industries, including the polymer industry and the oil industry.