L. Brasche

Nonlinear Acoustics, a Technique to Determine Microstructural Changes in Materials

An important aspect of nondestructive evaluation is materials characterization, in particular, detection of changes in the microstructure, affecting the mechanical properties. The goal of this project is to correlate the mechanical properties of high strength alloys with nonlinear acoustical properties of the materials. Many high strength alloys are precipitation hardened, and therefore, their mechanical properties are dependent on microstructural changes during thermal aging. Since the precipitates are formed by diffusion a property sensitive to the precipitation changes is the electrical resistivity. Standard ultrasonic techniques, on the other hand, have been unreliable in microstructural characterization, since in these alloys linear acoustic properties (e.g. sound velocity, attenuation) change by no more than 1%. Literature indicates however that nonlinear acoustical properties change by roughly 50% [1]. From this evidence it appears a nonlinear acoustic technique would be an additional method to examine microstructural changes in precipitation hardened materials.

Monitoring Fatigue Damage Accumulation with Rayleigh Wave Harmonic Generation Measurements

The use of nonlinear acoustics, and in particular harmonic generation, continues to gain interest as a means to characterize microstructural changes in engineering materials as a result of processing and in‐service conditions. Typical measurements involve the propagation of a monochromatic longitudinal wave toneburst through the bulk of a sample in a through‐transmission arrangement. This arrangement is not well suited for field applications, where two sided access is limited and parallel surfaces are rare. Harmonic generation measurements to monitor fatigue damage in acro engine alloys subject to fatigue will be presented. The use of Rayleigh waves has allowed one sided access and accommodates a small amount of surface curvature while restricting the probing wave to the surface where fatigue damage is typically initiated. Early results using uncalibrated receiving transducers on Ni‐based alloys demonstrate a sensitivity to damage accumulation in low cycle fatigue, where damage is spread over the sample s...

Sensitivity analysis of simulations for magnetic particle inspection using the finite-element method

In this article, we report a sensitivity analysis of numerical simulations of MPI for defects with various sizes using the finite element analysis (FEM).

Model‐Assisted Probability of Detection Validation for Immersion Ultrasonic Application

Model assisted probability of detection (MAPOD) is a method of calculating probability of detection versus flaws size curves which utilize physics‐based models to reduce the time, cost, and complexity of POD studies with respect to those conducted by purely empirical approaches. An approach to utilizing models combined with empirical data in calculating POD curves based on immersion ultrasonics as the example case is described. Before MAPOD calculations can be performed, the applicable physics‐based model must be validated to accuracy consistent with the desired accuracy of the resulting POD curve. In this case, the Thompson‐Gray ultrasonic measurement model was used. For the purposes of validating the MAPOD approach, a specimen was configured that would allow empirical data to be collected that would serve the dual purpose of providing input to the MAPOD calculation as well as providing input to empirical POD calculations (MIL‐HDBK‐1823). Validation of the MAPOD approach consisted of directly comparing t...

Analytical approach for fast computation of magnetic flux leakage due to surface defects

In this work, a fast analytical expression for the magnetic flux leakage due to a surface defect rotated at arbitrary angle to the external applied magnetic field was developed. The analytical results were compared with the numerical results (based on finite element method) and showed excellent agreement. The current work represents an important advancement in the development of fast algorithms for the simulation of magnetic flux leakage for magnetic non-destructive inspection such as magnetic flux leakage (MFL) or magnetic particle inspection (MPI).

Correlation of mechanical properties with non-destructive evaluation measurements in AlLi alloys

Abstract Selected mechanical, electrical and other physical properties were measured for both an Al-2.2wt.%Li binary alloy and aluminum alloy Al 2090, a commercial alloy, to determine the feasibility of a non-destructive evaluation (NDE) of the mechanical properties of AlLi alloys. A series of thermal aging processes was performed to produce a broad range of precipitate states and morphologies which strongly affect the mechanical properties of these alloys. Correlations between mechanical properties, obtained in uniaxial tension, and quantities measured by using NDE techniques are reported. The mechanical properties included yield stress and ultimate tensile strength. The NDE measurements included the Vickers hardness, electrical conductivity, eddy current response, and acoustic velocity and attenuation. The observed relationships between the mechanical property values and the NDE data are discussed. The detection of the T 1 phase by the combined use of eddy current (or d.c. conductivity) and hardness measurements is of particular interest.

Nondestructive Characterization and Bond Strength of Solid-Solid Bonds

With increasing demand in industry to produce solid-solid bonds, the need for their quantitative characterization, particularly with respect to their strength, becomes more urgent. In the present paper, restricted to diffusion bonds in metallic systems, we define strength as the ultimate engineering stress achieved in a uniaxial tensile test at slow strain rate. It is assumed that the reduction of strength is basically determined by a lack of metallic bonding over a fraction of the total area to be bonded, with metallically bonded areas being separated by crack-shaped voids. In the present paper, these voids are considered to contain a vacuum or, at most, a low pressure gas. In principle, they could be filled with some form of a solid contaminant (oxide, e.g.) which increases the complexity of the analysis[1]. Furthermore, the present paper concentrates on a situation where self-diffusion, necessary to achieve bonding, is the only metallurgical effect considered. Any phase transformations, precipitate reactions and grain growth during the bonding process are ignored. In addition, the materials on either side of the bond are identical.

Development of Modeling and Simulation for Magnetic Particle Inspection Using Finite Elements

Magnetic particle inspection (MPI) is a widely used inspection method for aerospace applications with inspection development essentially limited to empirical knowledge and experience‐based approaches. Better quantitative understanding of the MPI technique and factors that affect its sensitivity and reliability would contribute not only to reductions in inspection design cost and time but also improvement of analysis of experimental data. We employed a finite element method (FEM) for numerical calculation because this is known to be suitable for complicated geometric objects such as the part shapes encountered in aviation components and defects of concern. Magnetic particles are usually soft magnetic materials and sensitive to the magnetic field distribution around them. They are easily attracted toward a high magnetic field gradient. Selection of magnetic field source, which produces a magnetic field gradient large enough to detect a small defect in the sample, is an important factor in magnetic particle ...

Review of progress in magnetic particle inspection

Magnetic particle inspection (MPI) has been widely utilized for decades, and sees considerable use in the aerospace industry with a majority of the steel parts being inspected with MPI at some point in the lifecycle. Typical aircraft locations inspected are landing gear, engine components, attachment hardware, and doors. In spite of its numerous applications the method remains poorly understood, and there are many aspects of that method which would benefit from in-depth study. This shortcoming is due to the fact that MPI combines the complicated nature of electromagnetics, metallurgical material effects, fluid-particle motion dynamics, and physiological human factors into a single inspection. To promote understanding of the intricate method issues that affect sensitivity, or to assist with the revision of industry specifications and standards, research studies will be prioritized through the guidance of a panel of industry experts, using an approach which has worked successfully in the past to guide fluor...

POD OF ULTRASONIC DETECTION OF SYNTHETIC HARD ALPHA INCLUSIONS IN TITANIUM AIRCRAFT ENGINE FORGINGS

The probability of detection (POD) of inspection techniques is a key input to estimating the lives of structural components such as aircraft engines. This paper describes work conducted as a part of the development of POD curves for the ultrasonic detection of synthetic hard alpha (SHA) inclusions in titanium aircraft engine forgings. The sample upon which the POD curves are to be based contains four types of right circular SHAs that have been embedded in a representative titanium forging, as well as a number of flat bottomed holes (FBHs). The SHAs were of two sizes, ♯3 and ♯5, with each size including seeds with nominal nitrogen concentrations of both 3 and 17 wt. %. The FBHs included sizes of ♯1, ♯3, and ♯5. This discreteness of the data poses a number of challenges to standard processes for determining POD. For example, at each concentration of nitrogen, there are only two sizes, with 10 inspection opportunities each. Fully empirical, standard methodologies such as a versus a provide less than an idea...