On the scattering of longitudinal elastic waves from axisymmetric defects in coated pipes

This is the post-print version of the final paper published in Journal of Sound and Vibration. The published article is available from the link below. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. Copyright @ 2013 Elsevier B.V.Viscoelastic coatings are widely used to protect pipelines from their surrounding environment. These coatings are known to attenuate ultrasonic waves guided along the pipe walls, which may limit the range of a pulse/echo based inspection technique that seeks to detect defects in a pipeline. This article aims to investigate the attenuation of longitudinal modes in a coated pipe by comparing predicted and measured values for the reflection coefficient of an axisymmetric defect in a pipe coated with bitumen. This extends recent work undertaken by the authors for torsional modes, and also provides an independent investigation into the validity of those values proposed by the authors for the shear properties of bitumen, based on a comparison between prediction and experiment for torsional modes. Predictions are generated using a numerical mode matching approach for axially uniform defects, and a hybrid finite element based method for non-uniform defects. Values for the shear and longitudinal properties of bitumen are investigated and it is shown that the shear properties of the viscoelastic material play a dominant role in the propagation of longitudinal modes in a coated pipeline. Moreover, by using the shear values obtained from experiments on torsional modes, it is shown that good agreement between prediction and measurement for uniform and non-uniform defects may also be obtained for the longitudinal L(0,2) mode. This provides further validation for the shear bulk acoustic properties proposed for bitumen in the low ultrasonic frequency range, although in order to apply this methodology in general it is demonstrated that one must measure independently the reflection coefficient of both the torsional T(0,1) and the longitudinal L(0,2) mode before arriving at values for the shear properties of a viscoelastic material

Finite Size and Speciment Thickness Influence in Acousto-Ultrasonic NDE

Acousto-ultrasonics (AU) uses a pair of transducers to characterize distributed damage in composite plates. A transducer placed normal to the surface creates resonances which propagate as plate waves. Once the receiving transducer picks up the signal, simple analysis techniques, such as the zeroth or first moment of the power spectrum, are applied to create a Stress Wave Factor (SWF). The SWF is then used to quantify the damage state of the composite once the system has been properly trained

Analisa Pengaruh Temperatur Tempering pada Perlakuan Panas Terhadap Perubahan Struktur Mikro dan Sifat Mekanik Coupler Yoke Rotary (AAR-M201 Grade E)

Salah satu bagian penting dari konstruksi komponen kereta api yaitu coupler yoke rotary yang digunakan sebagai penyambung gerbong kereta api. Kegagalan yang sering terjadi adalah ketika coupler yoke rotary sesudah diberikan perlakuan panas, sifat mekanisnya tidak memenuhi standar, sehingga perlu dilakukan proses perlakuan panas lain yaitu hardening dan tempering. Tujuan penelitian ini adalah menganalisa pengaruh temperatur tempering terhadap perubahan struktur mikro dan sifat mekanik baja AAR M201 Grade E. Hasil penelitian menunjukkan bahwa struktur mikro pada baja AAR-M201 Grade E, hasil dari proses tempering pada temperatur 250oC adalah upper bainit. Proses tempering pada temperatur 300oC menghasilkan upper bainit yang lebih kasar. Proses tempering pada temperatur 350oC menghasilkan upper bainit disertai ferit dan perlit. Peningkatan temperatur tempering mengakibatkan struktur menjadi semakin kasar dan perubahan fasa. Perlakuan hardening selama 3 jam disertai tempering pada temperature 350oC selama 1 jam paling mendekati spesifikasi dari sifat mekanik pada baja AAR-M201 Grade E dengan nilai kekuatan luluh 854,53 MPa, kekuatan maksimum 979,16 MPa, persen elongasi 4,13%, dan reduksi area 8,33%. Peningkatan temperatur tempering menurunkan kekuatan luluh, kekuatan maksimum, dan kekerasan serta meningkatkan keuletan dan energi impak. ============================================================================================================== One of the important parts train construction is couple yoke rotary used for connection of railway carriages. Failure that often occurs after couple yoke rotary got normalizing process and it does tensile test, result from mechanical properties is not meet the standard so that need to do another heat treatment process, that is hardening and tempering. The purpose of this research are analysis of temperature variation of tempering for microstructure transformation of the AAR-M201Grade E steel and analysis of temperature variation of tempering for mechanical properties of the AAR-M201Grade E steel. The result of this research for tempering at 250oC is upper bainit microstructure. The result for tempering at 300oC is upper bainit microstructure with coarse grain. The result for tempering at 350oC are upper bainit, ferrite, and pearlite microstructure. Increasing of tempering temperature make coarse microstructure and transformation phase. Temperature tempering influence mechanical properties of the AAR-M201 Grade E steel. Increasing of tempering temperature decrease yield strength, tensile strength, and hardness, it also increase ductility and impact energy

Generation of guided waves in hollow cylinders by wedge and comb type transducers

It was shown by Denos C. Gazis in 19591 that in linearly elastic hollow circular cylinders there exists an infinite number of “normal modes”, each of which has its own propagation characteristics such as phase and group velocity as well as their own displacement and stress distributions throughout the cross section of the cylinder. It was also shown that, even for a given mode, these characteristics changed with changing frequency. In general, when such a cylinder is loaded by external forces, all of the modes of the structure will be excited in varying strengths determined by the characteristics of the applied loading. From a nondestructive evaluation (NDE) point of view, however, there are some modes which, due to their unique characteristics, are more sensitive to the quantities being measured or the defects being sought. It would be advantageous, therefore, to modify the applied loading so as to excite with appreciable amplitude only those modes which are found to be sensitive to the quantity being measured. In order to do this however, the relationship between the applied loading and the amplitudes of the generated modes must be understood. In this paper, the general problem of determining the amplitudes with which each propagating mode is generated due to the application of specific types of separable, time harmonic loading is investigated. (The more general problem of non-separable loading can be found in a recent paper2). The general results for separable loading are then specialized to two types of transducers commonly used in NDE to determine how the parameters of these two types of sources affect the amplitudes of the generated modes

UPAYA GURU DALAM MENINGKATKAN MINAT BELAJAR MATEMATIKA SISWA KELAS V SD SELAMA PEMBELAJARAN DARING

Perubahan sistem pembelajaran ini salah satunya mempengaruhi minat belajar siswa, khususnya pada pelajaran matematika. Minat belajar siswa tidak bisa dipaksakan tetapi dapat dirangsang dengan bantuan guru. Tujuan penelitian ini untuk 1) mendeskripsikan pelaksanaan pembelajaran matematika selama pembelajaran daring. 2) mendeskripsikan upaya yang dilakukan guru dalam meningkatkan minat belajar matematika selama pembelajaran daring. 3) mengetahui faktor pendukung dan penghambat guru dalam meningkatkan minat belajar matematika selama pembelajaran daring. Penelitian ini menggunakan pendekatan kualitatif dengan metode deskriptif. Teknik pengumpulan data menggunakan observasi, wawancara dan dokumentasi. Data yang terkumpul, kemudian dianalisis dengan teknik triangulasi data. Hasil dari penelitian ini adalah 1) pelaksanaan pembelajaran matematika selama pembelajaran daring memiliki tiga tahap yaitu: perencanaan pembelajaran, proses pembelajaran dan evaluasi pembelajaran. 2) upaya guru dalam meningkatkan minat belajar matematika selama pembelajaran daring yaitu: menjelaskan tujuan pembelajaran terlebih dahulu, memberikan motivasi kepada siswa, memberikan bimbingan belajar, menggunakan metode dan media yang bervariasi, dan memberikan Reward. 2) faktor pendukung guru dalam meningkatkan minat belajar matematika selama pembelajaran daring yaitu orang tua dan fasilitas, sedangkan faktor penghambat guru dalam meningkatkan minat belajar matematika selama pembelajaran daring yaitu pembagian waktu, jaringan internet dan gadget

Utility of Lamb Waves for Near Surface Crack Detection

Ultrasonic waves have a long history in detection of surface breaking cracks. Attempts are being made to use guided waves as a defect detection tool in aging skin structures in aircrafts and in the power generation industries as these waves offer a great advantage over conventional bulks waves. Guided waves can be excited at one position and allowed to propagate considerable distances before attenuating. Depending on the configuration employed for defect detection, reflected or received waveforms give information regarding the integrity of the structure along the line of sight. This description makes the technique look rather simple. Particularly, NDT utilizing Lamb waves is more complex due to the existence of two or more modes at any given frequency. Success was reported by several authors on defect detection using Lamb waves. Brief or no explanation was given on the reasons behind the choice of specific excitation frequencies and incident angles. The emphasis was solely on the defect detection aspects

Pengaruh Brand Equity terhadap Purchase decision pada Produk Laptop Merek Acer di Kota Payakumbuh

Tujuan dari penelitian ini adalah untuk mengetahui pengaruh Brand Equity terhadap Purchase Decision pada produk laptop merek Acer di Kota Payakumbuh. Jenis penelitian dalam penelitian ini adalah Explanatory Research. Data penelitian ini dikumpulkan melalui kuesioner dengan responden nya adalahkonsumen yang menggunakan laptop merek Acer di Kota Payakumbuh. Ukuran sampel pada penelitian berjumlah 120 responden. Teknik sampel yang digunakan adalah Purposive Sampling (Judgement Sampling). Teknik analisis data yang digunakan datam penelitian ini menggunakan Analisis Regresi Linear Berganda. Pengolahan data dalam penelitian ini menggunakan software SPSS versi 22. Hasil dari penelitian menemukan bahwa adanya pengaruh signifikan Brand Awareness dan Brand Loyalty terhadap Purchase Decision, serta menemukan bahwa adanya pengaruh yang tidak signifikan Perceived Quality dan Brand Association terhadap Purchase Decision. Kata Kunci :, Brand Association, Brand Awareness, Brand Loyalty, Perceived Qualit

INVENTARISASI JENIS-JENIS BURUNG DI HUTAN KALAWEIT SUPAYANG, SOLOK, SUMATERA BARAT

Hutan Kalaweit Supayang merupakan kawasan hutan konservasi yang dikelola oleh Yayasan Kalaweit Indonesia dan digunakan sebagai area konservasi satwa liar. Kawasan seluas 317 ha ini berada di perbukitan dengan ketinggian 600-1.050 mdpl, mempunyai vegetasi yang cukup baik, jauh dari pemukiman sehingga menjadikan kawasan ini berpotensi memiliki jenis-jenis burung yang beragam. Penelitian tentang Inventarisasi Jenis-jenis Burung di Hutan Kalaweit Supayang, Solok, telah dilakukan selama 20 hari pengamatan dari bulan Agustus sampai Oktober 2018 dengan menggunakan metode survey dan observasi langsung menggunakan teknik daftar jenis 20 burung (MacKinnon). Hasil penelitian telah mencatat sebanyak 73 jenis burung yang termasuk kedalam 54 genera, 30 famili dan 8 ordo. 13 jenis burung berstatus mendekati terancam punah (Neart Threatened), satu jenis berstatus Rentan (Vulnerable) dan satu jenis berstatus terancam punah (Endangered) menurut IUCN Redlist, sepuluh jenis tercantum dalam Appendix II CITES dan 23 jenis dilindungi oleh perundang-undangan Republik Indonesia. Sedangkan lima jenis endemik untuk wilayah Republik Indonesia (Sumatera, Jawa, dan Bali), dan empat jenis adalah pengunjung musim dingin. Hasil yang diperoleh terbilang banyak, hampir sebanding dengan jenis burung yang ditemukan di Gunung Tandikat, yaitu 88 jenis

Ultrasonic Guided Waves for Lap Splice Joint Inspection in Aging Aircraft

The integrity and reliability of adhesive joints in structural applications has long been a critical issue. Failure of these bonds during service could be catastrophic. In particular, the aviation industry due to its progressively aging fleet calls for a reliable non-destructive testing technique to characterize the bond quality. Several NDE techniques were developed each with its own advantages and disadvantages. [1–2] Utilization of ultrasonic guided waves offer a reliable and time efficient method. [3] Following several laboratory studies this technique was tested on a service damaged aircraft at Sandia National Laboratories in Albuquerque, NM. A Double Spring Hopping Probe (DSHP) was developed and tested on this test bed. A protocol for the inspection of lap splices and tear strap was established. The concepts of utilization of wave structure in mode selection, angle and frequency tuning for optimal use of the Lamb type guided waves are addressed. Highlights of our recent work on aging aircraft inspection are presented in this paper. The work expands on our earlier presentations. [4