Hyeon Cho

Development of an intelligent system for ultrasonic flaw classification in weldments

Abstract Even though ultrasonic pattern recognition is considered as the most effective and promising approach to flaw classification in weldments, its application to the realistic field inspection is still very limited due to the crucial barriers in cost, time and reliability. To reduce such barriers, previously we have proposed an intelligent system approach that consisted of the following four ingredients: (1) a PC-based ultrasonic testing (PC-UT) system; (2) an effective invariant ultrasonic flaw classification algorithm; (3) an intelligent flaw classification software; and (4) a database with abundant experimental flaw signals. In the present work, for performing the ultrasonic flaw classification in weldments in a real-time fashion in many real word situations, we develop an intelligent system, which is called the ‘Intelligent Ultrasonic Evaluation System (IUES)’ by the integration of the above four ingredients into a single, unified system. In addition, for the improvement of classification accuracy of flaws, especially slag inclusions, we expand the feature set by adding new informative features, and demonstrate the enhanced performance of the IUES with flaw signals in the database constructed previously. And then, to take care of the increased redundancy in the feature set due to the addition of features, we also propose two efficient schemes for feature selection: the forward selection with trial and error, and the forward selection with criteria of the error probability and the linear correlation coefficients of individual features.

Short-circuit dispatch: accelerating virtual machine interpreters on embedded processors

Interpreters are widely used to implement high-level language virtual machines (VMs), especially on resource-constrained embedded platforms. Many scripting languages employ interpreter-based VMs for their advantages over native code compilers, such as portability, smaller resource footprint, and compact codes. For efficient interpretation a script (program) is first compiled into an intermediate representation, or bytecodes. The canonical interpreter then runs an infinite loop that fetches, decodes, and executes one bytecode at a time. This bytecode dispatch loop is a well-known source of inefficiency, typically featuring a large jump table with a hard-to-predict indirect jump. Most existing techniques to optimize this loop focus on reducing the misprediction rate of this indirect jump in both hardware and software. However, these techniques are much less effective on embedded processors with shallow pipelines and low IPCs. Instead, we tackle another source of inefficiency more prominent on embedded platforms - redundant computation in the dispatch loop. To this end, we propose Short-Circuit Dispatch (SCD), a low cost architectural extension that enables fast, hardware-based bytecode dispatch with fewer instructions. The key idea of SCD is to overlay the software-created bytecode jump table on a branch target buffer (BTB). Once a bytecode is fetched, the BTB is looked up using the bytecode, instead of PC, as key. If it hits, the interpreter directly jumps to the target address retrieved from the BTB, otherwise, it goes through the original dispatch path. This effectively eliminates redundant computation in the dispatcher code for decode, bound check, and target address calculation, thus significantly reducing total instruction count. Our simulation results demonstrate that SCD achieves geomean speedups of 19.9% and 14.1% for two production-grade script interpreters for Lua and JavaScript, respectively. Moreover, our fully synthesizable RTL design based on a RISC-V embedded processor shows that SCD improves the EDP of the Lua interpreter by 24.2%, while increasing the chip area by only 0.72% at a 40nm technology node.

Typed Architectures: Architectural Support for Lightweight Scripting

Dynamic scripting languages are becoming more and more widely adopted not only for fast prototyping but also for developing production-grade applications. They provide high-productivity programming environments featuring high levels of abstraction with powerful built-in functions, automatic memory management, object-oriented programming paradigm and dynamic typing. However, their flexible, dynamic type systems easily become the source of inefficiency in terms of instruction count, memory footprint, and energy consumption. This overhead makes it challenging to deploy these high-productivity programming technologies on emerging single-board computers for IoT applications. Addressing this challenge, this paper introduces Typed Architectures, a high-efficiency, low-cost execution substrate for dynamic scripting languages, where each data variable retains high-level type information at an ISA level. Typed Architectures calculate and check the dynamic type of each variable implicitly in hardware, rather than explicitly in software, hence significantly reducing instruction count for dynamic type checking. Besides, Typed Architectures introduce polymorphic instructions (e.g., xadd), which are bound to the correct native instruction at runtime within the pipeline (e.g., add or fadd) to efficiently implement polymorphic operators. Finally, Typed Architectures provide hardware support for flexible yet efficient type tag extraction and insertion, capturing common data layout patterns of tag-value pairs. Our evaluation using a fully synthesizable RISC-V RTL design on FPGA shows that Typed Architectures achieve geomean speedups of 11.2% and 9.9% with maximum speedups of 32.6% and 43.5% for two production-grade scripting engines for JavaScript and Lua, respectively. Moreover, Typed Architectures improve the energy-delay product (EDP) by 19.3% for JavaScript and 16.5% for Lua with an area overhead of 1.6% at a 40nm technology node.

Feasibility on Ultrasonic Velocity using Contact and Non‐Contact Nondestructive Techniques for Carbon/Carbon Composites

Advanced materials are to be required to have specific functions associated with extremely environments. One of them is carbon/carbon(C/C) composite material, which has obvious advantages over conventional materials. The C/Cs have become to be utilized as parts of aerospace applications and its low density, high thermal conductivity and excellent mechanical properties at elevated temperatures make it an ideal material for aircraft brake disks. Because of permeation of coupling medium such as water, it is desirable to perform contact‐less nondestructive evaluation to assess material properties and part homogeneity. In this work, a C/C composite material was characterized with non‐contact and contact ultrasonic methods using a scanner with automatic‐data acquisition function. Also through transmission mode was performed because of the main limitation for air‐coupled transducers, which is the acoustic impedance mismatch between most materials and air. Especially ultrasonic images and velocities for C/C compo...

Ultrasonic Measurement of Gap Size in an Epoxy Layer between a Steel Sheet and Fiber Reinforced Plastics

Detection and sizing of empty gaps caused by missing adhesive are of great importance for quality assurance of multi-layer structures with a thin epoxy adhesive layer. This paper describes an approach and instrumentation for sizing empty gaps existed in adhesive layer between a thin steel sheet and fiber reinforced plastics by the combination of higher-frequency pulse-echo measurement and lower-frequency resonance spectroscopy of ultrasound. In this approach, the ultrasonic reflection from the interface between the steel sheet and the epoxy adhesive is measured with a high-frequency pulse-echo setup in order to identify contact disbanding and missing adhesive. Then, the steel sheet is excited to resonance by low-frequency ultrasound, and the gap size underneath the measuring location is estimated from the resonance responses. For practical application in industry an automated testing system has been developed where the proposed approach is implemented. The performance of the proposed approach has been verified by actual measurement of gap sizes from the cross-sections of cut specimens using an optical microscope.

An Ultrasonic Nondestructive Method for Evaluating Carbon/Carbon Composites

In this work, especially carbon/carbon (C/C) composites are one of the few materials that are suitable for structural applications at high temperature environments. Characterization and integrity of carbon/carbon(C/C) composite materials should be evaluated because of its inhomogeneity and composite. A C/C composite material was nondestructively characterized and a technique was developed to measure ultrasonic velocity in C/C composites using automated data acquisition software. We have proposed a peak‐delay measurement method based on the pulse overlap measurement method. Also through transmission mode was performed to compare ultrasonic velocity with the above peak‐delay measurement method in an immersion tank. The variation of ultrasonic velocity was measured and found to be consistent with those in a large C/C composite manufactured by chemical vapor infiltration (CVI) method. These results were compared with that obtained by dry‐coupling ultrasonics. A peak‐delay measurement method well corresponded ...

Inspecting Carbon Matrix Composites with Airborne/Conventional Ultrasound

Carbon/phenolic composite (CPC) materials have obvious advantages over conventional materials, which are consisting of carbon fibers embedded in a carbon matrix. The CPCs have become to be utilized as parts of aerospace applications and its low density, high thermal conductivity and excellent mechanical properties at elevated temperatures make it an ideal material for aircraft brake disks. Because of permeation of coupling medium such as water, it is desirable to perform contact-less nondestructive evaluation to assess material properties and part homogeneity. In this work, a C/P(Carbon/phenolic) composite material was characterized with non-contact and contact ultrasonic methods using automated acquisition scanner. Also through transmission mode was performed because of the main limitation for air-coupled transducers, which is the acoustic impedance mismatch between most materials and air. Especially ultrasonic images and velocities for C/C(Carbon/Carbon) composite disk brake was measured and found to be consistent to some degree with the non-contact and contact ultrasonic measurement methods. Low frequency throughtransmission scans based on both amplitude and time-of-flight of the ultrasonic pulse were used for mapping out the material property inhomogeneity. Measured results were compared with those obtained by the motorized system with using dry-coupling ultrasonics and through transmission method in immersion. Finally, results using a proposed peak-delay measurement method well corresponded to ultrasonic velocities of the pulse overlap method.

Ultrasonic Inspection of Carbon/ Phenolic Composites Using a Peak-Delay Measurement Method

Carbon/phenolic composite (CPC) materials are unique which consist of carbon fibers embedded in a carbon matrix. The CPCs are originally developed for aerospace applications and its low density, high thermal conductivity and excellent mechanical properties at elevated temperatures make it an ideal material for aircraft brake disks. The properties of the CPC are dependent on the manufacturing methods used for production and fiber arrangement. It is desirable to perform nondestructive evaluation to assess material properties and part homogeneity in order to ensure product quality and structural integrity of CPC brake disks. In this work, a CPC material was nondestructively characterized and a technique was developed to measure ultrasonic velocity in C/P composites using automated data acquisition software. Also a motorized system was adopted to measure ultrasonic velocity on the point of CPC materials under the same coupling conditions. Manual results were compared with those obtained by the motorized system with using drycoupling ultrasonics and through transmission method in immersion. A peak-delay measurement method well corresponded to ultrasonic velocities of the pulse overlap method and throughtransmission mode and C-scan image signal based on peak-to-peak amplitude.

ULTRASONIC CHARACTERIZATION OF CARBON/CARBON COMPOSITES BASED ON A PEAK-DELAY MEASUREMENT METHOD

In this work, a C/C composite material was nondestructively characterized and a technique was developed to measure ultrasonic velocity in C/C composites using automated data acquisition software. We have proposed a peak-delay measurement method based on the pulse overlap measurement method. Also through transmission mode was performed to compare ultrasonic velocity with the above peak-delay measurement method in an immersion tank. The variation of ultrasonic velocity was measured and found to be consistent with those in a large C/C composite. These results were compared with that obtained by dry-coupling ultrasonics. For mapping out the material property inhomogeneity, through-transmission scans were used based on both amplitude and time-of-flight of the ultrasonic pulse. A peak-delay measurement method well corresponded to the ultrasonic velocities of the pulse overlap method and through-transmission mode and C-scan image signal.

A Study on Ultrasonic Evaluation of Material Homogeneity in Wood

In this work, a wood material was nondestructively characterized and a technique was developed to measure ultrasonic velocity in wood using automated data acquisition software. It is desirable to perform nondestructive evaluation (NDE) to assess material properties and absorption of wood because wood is a natural composite and often inhomogeneity. Several ultrasonic techniques were applied to wood for the evaluation of variations material properties. The variation of ultrasonic velocity was measured and found to be somewhat consistent with those in infiltrated area in the course of nature absorption. Low frequency (1MHz) through‐transmission scans based on both amplitude and time‐of‐flight of the ultrasonic pulse were used for mapping out the material property inhomogeneity. These results were compared with those obtained by dry‐coupling ultrasonics. A good correlation was found between ultrasonic velocity (a pulse overlap and peak‐delay measurement method) and C‐scan image signal based on peak‐to‐peak am...