• 비파괴검사학회지
• /
• 제36권3호
• /
• pp.175-180
• /
• 2016

Nondestructive evaluation for material health monitoring is important in aerospace industries. Composite laminates are exposed to heat cyclic loading and humid environment depending on flight conditions. Cyclic heat loading and moisture absorption may lead to material degradation such as matrix breaking, debonding, and delamination. In this paper, the moisture absorption ratio was investigated by measuring the Lamb wave velocity. The composite laminates were manufactured and subjected to different thermal aging cycles and moisture absorption. For various conditions of these cycles, not only changes in weight and also ultrasonic wave velocity were measured, and the Lamb wave velocity at various levels of moisture on a carbon-epoxy plate was investigated. Results from the experiment show a linear correlation between moisture absorption ratio and Lamb wave velocity at different thermal fatigue stages. The presented method can be applied as an alternative solution in the online monitoring of composite laminate moisture levels in commercial flights.

• Asian-Australasian Journal of Animal Sciences
• /
• 제5권3호
• /
• pp.469-473
• /
• 1992

Data on the birth weight, 8 week body weight and ewe body weight of an unselected random mating Romney Marsh sheep flock are analyzed to study the influence of various environmental factors. The average birth weight of lambs was 5.06 kg. Sex of lamb, birth type and dam age contributed significant variation in lamb birth weight (p < 0.05). Males were significantly heavier than females (p < 0.05) and singles were significantly heavier than multiples (p < 0.05) at birth. Birth weight of lamb increased with the progress of dams' age. The overall average 8 week body weight of lambs was 20.84 kg. Effect of birth weight, sex, birth type and dam age was significant on 8 week body weight of lamb. Eight week body weight increased with the increase of lamb birth weight (b=1.285 kg). Ewes' body weight taken before tupping was affected by ewes' age, year of performance and their weight at birth. It was concluded that performance data on lamb birth weight, 8 week body weight and ewe body weight should be corrected for the above relevantly significant environmental factors in any genetic calculation in the United Kingdom Romney March sheep.

• 한국신재생에너지학회:학술대회논문집
• /
• 한국신재생에너지학회 2005년도 춘계학술대회
• /
• pp.542-545
• /
• 2005

This paper is concerned wi th the generation of the Lamb waves in a non­ferromagnetic plate by a recently-developed orientation-adjustable patch-type magnetostrictive transducer (OPMT) and the dispersion analysis from the measured Lamb waves. OPMT is capable of adjusting wave-propagation orientation only with a single installation on a plate. The mechanics behind the wave generation and measurement by the magnetostrictive phenomenon, the working principle of OPMT is explained and the actual generation and measurement of the Lamb waves were conducted in a 3 mm-thick aluminum plate. For the accurate analysis of the dispersion characteristics of the measured Lamb waves, a modified version of the short-time Fourier transform, known as the dispersion-based short-time Fourier transform, was employed. The results presented in this work would serve as the underlying research for an advanced non-destructive evaluation based on ultrasonic waves.

• 한국소음진동공학회논문집
• /
• 제15권1호
• /
• pp.53-62
• /
• 2005

This study presents the NDE (non-destructive evaluation) technique for detecting the loosened bolts on joint steel structures on the basis of TOF (time of flight) and amplitudes of Lamb waves. Probabilistic neural network (PNN) technique which is an effective tool for pattern classification problem was applied to the damage estimation using PZT induced Lamb waves. Two kinds of damages were introduced by dominant damages (DD) which mean loosened bolts within the Lamb waves beam width and minor damages (MD) which mean loosened bolts out of the Lamb waves beam width. They were investigated for the establishment of the optimal decision boundaries which divide each damage class's region including the intact class. In this study, the applicability of the probabilistic neural networks was identified through the test results for the damage cases within and out of wave beam path. It has been found that the present methods are very efficient and reasonable in predicting the loosened bolts on the joint steel structures probabilistically.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2004년도 추계학술대회논문집
• /
• pp.625-632
• /
• 2004

This study presents the NDE (non-destructive evaluation) technique for detecting the loosened bolts on joint steel structures on the basis of TOF (time of flight) and amplitudes of Lamb waves. Probabilistic neural network (PNN) technique which is an effective tool for pattern classification problem was applied to the damage estimation using PZT induced Lamb waves. Two kinds of damages were introduced by dominant damages (DD) which mean loosened bolts within the Lamb waves beam width and minor damages (MD) which mean loosened bolts out of the Lamb waves beam width. They were investigated for the establishment of the optimal decision boundaries which divide each damage class's region including the intact class. In this study, the applicability of the probabilistic neural networks was identified through the test results for the damage cases within and out of wave beam path. It has been found that the present methods are very efficient and reasonable in predicting the loosened bolts on the joint steel structures probabilistically.

• 비파괴검사학회지
• /
• 제30권5호
• /
• pp.458-463
• /
• 2010

음향 비선형성은 재료 물성의 미세한 변화에 민감하기 때문에, 이를 측정하는 비선형 초음파 기술은 재료의 열화나 피로를 평가할 수 있는 기법으로 연구되어 왔다. 하지만 벌크파를 이용하는 일반적인 비선형 초음파 기법은 얇은 판재에 적용하는 것에는 여러 한계가 있다. 이와 같은 경우에는 비선형 Lamb 파의 사용을 생각할 수 있지만, Lamb 파는 벌크파와 매우 다른 전파 특성을 가지고 있어 그 비선형 특성에 대한 별도의 연구를 필요로 한다. 이를 위해 본 연구에서는 Lamb 파에서 비선형성에 의해 전파하면서 누적 성장할 수 있는 2차 고조파 모드의 발생 조건을 분석하였으며, 그 결과 네 가지 조건, 즉 (1) phase matching, (2) non-zero power flux, (3) group velocity matching, (4) non-zero out-of-plane displacement 를 제시하였다. 그리고 제시된 조건으로 알루미늄 판재에 대책 실험한 결과 이론 예측과 동일하게 전파 거리에 따라 2차 고조파 성분의 크기와 비선형 파라미터가 증가하였고, Al6061-T6 과 Al1100-H14에서 측정된 상대적인 비선형 파라미터의 비율이 이론적인 비율과 근접함을 보였다.

• 한국축산식품학회지
• /
• 제41권5호
• /
• pp.802-815
• /
• 2021

To investigate the effect of postmortem phases on lamb meat quality, the physicochemical quality, microstructure and water mobility of oyster cut, short loin, knuckle and silverside muscles from Small-Tail Han sheep were evaluated in the pre-rigor, rigor mortis and post-rigor phases. Pre-rigor lamb meat had higher pH and water holding capacity (WHC), whereas lower CIE L^*, b^*, hue angle values than rigor mortis and post-rigor meat (p<0.05). The Warner-Bratzler shear force (WBSF) values were higher in rigor mortis short loin and silverside than their pre-rigor and post-rigor counterparts, pre-rigor short loin had lower WBSF value than its post-rigor counterpart (p<0.05). Muscle fibers shrank laterally and longitudinally during the onset of rigor mortis. Rigor mortis and postrigor lamb meat exhibited wide I-bands, dark A-bands, short sarcomeres and large inter-myofibrillar spaces. The shift of immobilized water to free water and repulsion from the intra-myofibrillar space to the extracellular space result in the increase of water loss in rigor mortis and post-rigor lamb meat. The results of the principal component analysis (PCA) indicated that rigor mortis and post-rigor lamb meat had similar quality properties but different from pre-rigor lamb meat. In conclusion, the lamb meat in the pre-rigor phase had good tenderness, color and WHC. The results of this research could provide some theoretical references for lamb meat production and processing.

• Asian-Australasian Journal of Animal Sciences
• /
• 제28권8호
• /
• pp.1209-1215
• /
• 2015

Since lamb is a commodity, producers cannot control the price of the product they sell. Therefore, managing production costs is a necessity. We explored the study of elasticities as a tool for basing decision-making in sheep production, and aimed at investigating the composition and elasticities of lamb production costs, and their influence on the performance of the activity. A representative sheep production farm, designed in a panel meeting, was the base for calculation of lamb production cost. We then performed studies of: i) costs composition, and ii) cost elasticities for prices of inputs and for zootechnical indicators. Variable costs represented 64.15% of total cost, while 21.66% were represented by operational fixed costs, and 14.19% by the income of the factors. As for elasticities to input prices, the opportunity cost of land was the item to which production cost was more sensitive: a 1% increase in its price would cause a 0.2666% increase in lamb cost. Meanwhile, the impact of increasing any technical indicator was significantly higher than the impact of rising input prices. A 1% increase in weight at slaughter, for example, would reduce total cost in 0.91%. The greatest obstacle to economic viability of sheep production under the observed conditions is low technical efficiency. Increased production costs are more related to deficient zootechnical indexes than to high expenses.

• 대한기계학회논문집A
• /
• 제40권11호
• /
• pp.919-925
• /
• 2016

본 연구에서는 비선형 체적파 혼합 기법의 선행연구를 토대로 램파 기법에 적용하여 램파 혼합 기법에 대한 연구를 수행하였다. 램파 혼합 기법의 타당성을 증명하기 위해 결함이 없는 시편과 부식에 의해 발생된 표면 결함이 있는 시편에 대해 실험을 진행하였다. 실험 대조군으로는 램파의 지배적인 면내변위와 면외변위를 가지는 모드 및 주파수로 선정하였다. 그 결과 램파 혼합 기법으로도 결함 검출이 가능하였고, 기존의 램파 기법의 경향성과 유사하게 나타났다. 그리고 이론과 동일한 지배적인 변위와 모드가 발생된 것을 확인 할 수 있었다. 그러나 결함 검출 성능은 측정 방법 및 단순 모드 선정에 따라 결정되는 것이 아니라 변위 비율에 따라 결정된다.

• 한국항공우주학회지
• /
• 제34권6호
• /
• pp.29-34
• /
• 2006

본 연구는 두께변화가 있는 복합소재 평판을 전파하는 램파의 전파특성을 실험을 통하여 살펴보았다. 상용 항공우주구조물에는 두께변화가 존재하는 부품이 많이 사용되고 있고 구조변화에 의해 두께가 변할 수도 있기 때문에 구조건전성 모니터링을 위하여 램파를 사용하고자 한다면, 이러한 구조물에 대한 램파의 특성을 면밀히 분석해 볼 필요가 있다. 본 연구는 얇은 두께의 PZT를 구조물 표면에 부착하여 실험을 수행하였다. 두께변화가 있는 전파경로를 선택하여 측정된 신호의 전파속도 및 주파수 분석 결과를 이상적 전파조건과 비교를 통하여 두께변화가 존재하는 영역에서 전파특성의 변화가 이루어지는 과정 중에 전이영역이 발생함을 제시하였다.