• Title/Summary/Keyword: failure modes

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MICROTENSILE BOND STRENGTH OF SELF-ETCHING AND SELF-ADHESIVE RESIN CEMENTS TO DENTIN AND INDIRECT COMPOSITE RESIN (간접 복합레진 합착 시 자가부식형과 자가접착형 레진시멘트의 상아질에 대한 미세인장 결합강도)

  • Park, Jae-Gu;Cho, Young-Gon;Kim, Il-Sin
    • Restorative Dentistry and Endodontics
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    • v.35 no.2
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    • pp.106-115
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    • 2010
  • The purpose of this study was to evaluate the microtensile bond strength (${\mu}TBS$), failure modes and bonding interfaces of self-etching and three self-adhesive resin cements to dentin and indirect composite resin. Cylindrical composite blocks (Tescera, Bisco Inc.) were luted with resin cements (PA: Panavia F 2.0, Kuraray Medical Inc., RE: RelyX Unicem Clicker, 3M ESPE., MA: Maxem, Kerr Co., BI: BisCem, Bisco Inc.) on the prepared occlusal dentin surfaces of 20 extracted molars. After storage in distilled water for 24 h, $1.0\;mm\;{\times}\;1.0\;mm$ composite-dentin beams were prepared. ${\mu}TBS$ was tested at a cross-head speed of 0.5 mm/min. Data were analyzed with one-way ANOVA and Tukey's HSD test. Dentin sides of all fractured specimens and interfaces of resin cements-dentin or resin cements-composite were examined at FESEM (Field Emission-Scanning Electron Microscope). In conclusion, PA and RE showed higher bond strength and closer adaptation than MA and BI when indirect composite blocks were luted to dentin using a self-etching and three self-adhesive resin cements.

Vibration Characteristics of a Wire-Bonding Ultrasonic Horn (와이어 본딩용 초음파 혼의 진동 특성)

  • Kim, Young Woo;Yim, Vit;Han, Daewoong;Lee, Seung-Yop
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.38 no.2
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    • pp.227-233
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    • 2014
  • This study investigates the vibration characteristics of a wire-bonding piezoelectric transducer and ultrasonic horn for high-speed and precise welding. A ring-type piezoelectric stack actuator is excited at 136 kHz to vibrate a conical-type horn and capillary system. The nodal lines and amplification ratio of the ultrasonic horn are obtained using a theoretical analysis and FEM simulation. The vibration modes and frequencies close to the driving frequency are identified to evaluate the bonding performance of the current wire-bonder system. The FEM and experimental results show that the current wire-bonder system uses the bending mode of 136 kHz as the principal motion for bonding and that the transverse vibration of the capillary causes the bonding failure. Because the major longitudinal mode exists at 119 kHz, it is recommended that the design of the current wire-bonding system be modified to use the major longitudinal mode at the excitation frequency and to minimize the transverse vibration of capillary in order to improve the bonding performance.

Behavior of RC Beam Strengthened with Advanced Lifting Hole Anchorage System (개선된 인양홀을 이용한 정착장치로 보강된 RC 보의 거동)

  • Oh, Min-Ho;Kim, Tae-Wan;Park, Sun-Kyu
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.14 no.3
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    • pp.91-99
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    • 2010
  • In order to strengthen RC structures, various strengthening methods have been used. Particularly, external tendon strengthening method is very popular method to strengthen damaged structures in terms of efficiency, ease, economics. In this study, improved anchorage elements using the lifting hole were proposed to strengthen PSC or RC girder without any damage. Two types of anchorage elements were proposed and these elements were applied on six RC beams. Also, three types of existing anchorage elements were applied on three RC beams. Otherwise, any anchorage element was not applied on one RC beam to used as a control beam. To analyse behavior of these elements, static load tests were carried out. Test variables were anchorage shapes, prestressing level on the steel bar and tendon profiles. Deflections, strains and modes of failure were recorded to examine the strengthening effects of the beams. Ductility index and tendon stress were analyzed by comparing cracking load, yielding load and ultimate load. As a result, proposed anchorage elements using lifting hole were superior to existing anchorage elements in terms of strengthening effect and furthermore, they showed ductile behavior based on energy method.

Damage and vibrations of nuclear power plant buildings subjected to aircraft crash part I: Model test

  • Li, Z.R.;Li, Z.C.;Dong, Z.F.;Huang, T.;Lu, Y.G.;Rong, J.L.;Wu, H.
    • Nuclear Engineering and Technology
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    • v.53 no.9
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    • pp.3068-3084
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    • 2021
  • Investigations of large commercial aircraft impact effect on nuclear power plant (NPP) buildings have been drawing extensive attentions, particularly after the 9/11 event, and this paper aims to experimentally assess the damage and vibrations of NPP buildings subjected to aircraft crash. In present Part I, two shots of reduce-scaled model test of aircraft impacting on NPP building were carried out. Firstly, the 1:15 aircraft model (weighs 135 kg) and RC NPP model (weighs about 70 t) are designed and prepared. Then, based on the large rocket sled loading test platform, the aircraft models were accelerated to impact perpendicularly on the two sides of NPP model, i.e., containment and auxiliary buildings, with a velocity of about 170 m/s. The strain-time histories of rebars within the impact area and acceleration-time histories of each floor of NPP model are derived from the pre-arranged twenty-one strain gauges and twenty tri-axial accelerometers, and the whole impact processes were recorded by three high-speed cameras. The local penetration and perforation failure modes occurred respectively in the collision scenarios of containment and auxiliary buildings, and some suggestions for the NPP design are given. The maximum acceleration in the 1:15 scaled tests is 1785.73 g, and thus the corresponding maximum resultant acceleration in a prototype impact might be about 119 g, which poses a potential threat to the nuclear equipment. Furthermore, it was found that the nonlinear decrease of vibrations along the height was well reflected by the variations of both the maximum resultant vibrations and Cumulative Absolute Velocity (CAV). The present experimental work on the damage and dynamic responses of NPP structure under aircraft impact is firstly presented, which could provide a benchmark basis for further safety assessments of prototype NPP structure as well as inner systems and components against aircraft crash.

Axial Compression of Stub Columns for Concrete-filled Square Steel Tubes (일축 압축력을 받는 콘크리트충전 각형강관 단주의 구조적 거동)

  • Yoo, Yeong-Chan
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.22 no.2
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    • pp.617-624
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    • 2021
  • Concrete-filled steel tubular columns can improve the strength and deformation capacity of structures, thereby enabling the development of efficient structures. The Korean design standard (KDS41) regarding concrete-filled steel tubular structures, established by the architectural institute of Korea in 2005, was revised in 2009 and 2016. The objective was to understand the compressive strengths and deformation capacity of stub columns for concrete-filled square steel tubes under uniaxial compression and validate the KDS41's standard code for necessary corrections. Experiments were conducted on 26 specimens with parameters, such as the width-thickness ratio of cold-formed square tubes. The following values of the stub columns for concrete-filled square steel tubes were obtained: compressive strengths, relationship between the axial load and axial displacement, and failure modes. An analysis of these results enabled an understanding of the concrete-filled effect and the influence of the wide-thickness ratio. The compressive strengths of filled concrete saw a 9% increase compared to a state of uniaxial stress, which must be noted in a future edition of KDS41. After benchmarking the results regarding square steel tubes generated by cold forming to the guidelines provided by the KDS41, the KDS41's value of 2.26 for the limiting width-to-thickness ratio for the compact section was found to be inflated. With a safety concern, this paper proposes a more conservative value of 1.35.

Investigating the effects of non-persistent cracks' parameters on the rock fragmentation mechanism underneath the U shape cutters using experimental tests and numerical simulations with PFC2D

  • Fu, Jinwei;Haeri, Hadi;Sarfarazi, Vahab;Abad, Sh. Mohamadi Bolban;Marji, Mohammad Fatehi;Saeedi, Gholamreza;Yu, Yibing
    • Structural Engineering and Mechanics
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    • v.83 no.4
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    • pp.495-513
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    • 2022
  • This paper aims to study the fracture mechanism of rocks under the 'u'shape cutters considering the effects of crack (pre-existing crack) distances, crack spacing and crack inclination angles. The effects of loading rates on the rock fragmentation underneath these cutters have been also studied. For this purpose, nine experimental samples with dimensions of 5 cm×10 cm×10 cm consisting of the non-persistent cracks were prepared. The first three specimens' sets had one non-persistent crack (pre-existing crack) with a length of 2 cm and angularity of 0°, 45°, and 90°. The spacing between the crack and the "u" shape cutter was 2 cm. The second three specimens" set had one non-persistent crack with a length of 2 cm and angularity of 0°, 45°, and 90° but the spacing between pre-existing crack and the "u" shape cutter was 4 cm. The third three specimens'set has two non-persistent cracks with lengths of 2 cm and angularity of 0°, 45° and 90°. The spacing between the upper crack and the "u" shape cutter was 2 cm and the spacing between the lower crack and the upper crack was 2 cm. The samples were tested under a loading rate of 0.005 mm/s. concurrent with the experimental investigation. The numerical simulations were performed on the modeled samples with non-persistent cracks using PFC2D. These models were tested under three different loading rates of 0.005 mm/s, 0.01 mm/sec and 0.02 mm/sec. These results show that the crack number, crack spacing, crack angularity, and loading rate has important effects on the crack growth mechanism in the rocks underneath the "u" shape cutters. In addition, the failure modes and the fracture patterns in the experimental tests and numerical simulations are similar to one another showing the validity and accuracy of the current study.

Effect on Shear Strength of Ceramic Surface Treatment Materials and Three Resin Cements to IPS Empress 2 (표면 처리재와 레진 시멘트가 IPS Empress 2의 전단결합강도에 미치는 영향)

  • Yae, Sun-Hae;Lee, Kyubok;Lee, Cheong-Hee
    • Journal of Dental Rehabilitation and Applied Science
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    • v.18 no.3
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    • pp.157-170
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    • 2002
  • The purpose of this study is to analyze the shear bond strength according to kinds of surface treatment agents and resin cements after acid etching of IPS Empress 2. For this purpose, test groups were classified into silane-treated bonding groups, silica-coated group and Targis link applied group. Then, nine bonding groups in total, each three groups per kind, were prepared by using three kinds of resin cements-Panavia F, Variolink II and Rely-X ARC, and thirty test specimens per group were prepared. To examine any changes in the oral environment, the shear bond strength of each test specimen was measured after dipping test for 24 hours and for five weeks, respectively, in distilled water at $37^{\circ}C$ and performing heat cycle 10,000 times in total, each 2,000 times per week, during a five weeks of dipping, under the condition similar to the oral environment. The bond failure modes were also observed by means of a scanning electron microscope. The results are summarized as follows 1. Statically significant differences between the surface conditioning materials were observed. The shear strength of the silane treatment was the highest of all three types of surface treatments(p<0.001). 2. Shear strengths varied significantly for different types of resin luting agents. But bond strength of Targis link surface treatments were not significantly different(p<0.05). 3. No significant difference of bonding strengths was found between storage time conditions(24 hours and 5 weeks). Only group II, IV, VII, IX were significantly different(p<0.05). 4. After thermocycling, the shear bond strengths of all groups were significantly decreased (p<0.05). Group III, V, VI were no significantly different. 5. On the SEM observation of fractured surfaces, all groups were shown complex failure.

Physical Properties and Detachment Characteristics of Persimmon Fruit (감 과실(果實)의 물리성(物理性)및 이탈특성(離脫特性))

  • Kim, Tae Han
    • Current Research on Agriculture and Life Sciences
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    • v.3
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    • pp.62-69
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    • 1985
  • In order to develop the mechanical fruit harvest system the detachment force, type and torque investigated and analyse as several loading modes were applied on the fruit-stem of the persimmon fruit. A proving ring with strain gauges was used for the experiment. The following conclusions were drawn from the results : The mode of withdrawl of the stem from the calyx appeared highly as the persimmon fruit matured. The mode of failure at the junction of the stem and calyx which was desirable mode for mechanical fruit harvest increased as the angular displacement of the fruit with respect to the stem axis increased from zero to ninety degrees. However the mode of failure of the fruiting branch decreased for the same degree of angle pull as above. The range of detachment force of the persimmon fruit was from 13 to 5 kg. The detachment force decreased from 47 to 8 % as the fruit matured. Also, the force decreased from 31 to 24 % for the same maturity levels as the angular displacement of the fruit with respect to the stem axis increased from zero to ninety degrees. The range of detachment force to weight ratio(F/W) of the fruit was from 130 to 54 approximately. The detachment force to weight ratio (F/W) decreased from 36 to 8 % as the fruit matured. Also, the ratio (F/W) decreased from 49 to 33 % for the same maturity levels as the same degree of angle pull as above. In order to remove fruit from tree the desirable force applied to the stem is approximately from 1,280 to 530 kg. Also, the desirable torque to remove the fruits was approximately from 1.1 to $0.5kg{\cdot}cm$.

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Some New Problems of International Aviation Security- Considerations Forcused on its Legal Aspects (최근국제항공보안대책(最近國際航空保安対策)의 제간제(諸間題) -특히 법적측면(法的測面)을 중심(中心)으로-)

  • Choi, Wan-Sik
    • The Korean Journal of Air & Space Law and Policy
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    • v.5
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    • pp.53-75
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    • 1993
  • This article is concerned with the comment on "Some New Problems of International Aviation Security-Considerations Forcused on its Legal Aspects". Ever since 1970, in addition to the problem of failure to accept the Tokyo, Hague and Montreal Conventions, there has been also the problem of parties to them, failing to comply with their obligations under the respective treaties, in the form especially of nominal penalties or the lack of any effort to prosecute after blank refusals to extradite. There have also been cases of prolonged detention of aircraft, passengers and hostages. In this regard, all three conventions contain identical clauses which submit disputes between two or more contracting States concerning the interpretation or application of the respective conventions to arbitration or failing agreement on the organization of the arbitration, to the International Court of Justice. To the extent to which contracting States have not contracted out of this undertaking, as I fear they are expressly allowed to do, this promision can be used by contracting States to ensure compliance. But to date, this avenue does not appear to have been used. From this point of view, it may be worth mentioning that there appears to be an alarming trend towards the view that the defeat of terrorism is such an overriding imperative that all means of doing so become, in international law, automatically lawful. In addition, in as far as aviation security is concerned, as in fact it has long been suggested, what is required is the "application of the strictest security measures by all concerned."In this regard, mention should be made of Annex 17 to the Chicago Convention on Security-Safeguarding International Civil Aviation against Acts of Unlawful Intereference. ICAO has, moreover, compiled, for restricted distribution, a Security Manual for Safeguarding Civil Aviation Against Acts of Unlawful Interference, which is highly useful. In this regard, it may well be argued that, unless States members of ICAO notify the ICAO Council of their inability to comply with opecific standards in Annex 17 or any of the related Annexes in accordance with Article 38 of the 1944 Chicago Convention on International Civil Aviation, their failure to do so can involve State responsibility and, if damage were to insure, their liability. The same applies to breaches of any other treaty obligation. I hope to demonstrate that although modes of international violence may change, their underlying characteristics remain broadly similar, necessitating not simply the adoption of an adequate body of domestic legislation, firm in its content and fairly administered, but also an international network of communication, of cooperation and of coordination of policies. Afurther legal instrument is now being developed by the Legal Committee of ICAO with respect to unlawful acts at International airports. These instruments, however, are not very effective, because of the absence of universal acceptance and the deficiency I have already pointed out. Therefore, States, airports and international airlines have to concentrate on prevention. If the development of policies is important at the international level, it is equally important in the domestic setting. For example, the recent experiences of France have prompted many changes in the State's legislation and in its policies towards terrorism, with higher penalties for terrorist offences and incentives which encourage accused terrorists to pass informations to the authorities. And our government has to tighten furthermore security measures. Particularly, in the case an unarmed hijacker who boards having no instrument in his possession with which to promote the hoax, a plaintiff-passenger would be hard-pressed to show that the airline was negligent in screening the hijacker prior to boarding. In light of the airline's duty to exercise a high degree of care to provide for the safety of all the passengers on board, an acquiescence to a hijacker's demands on the part of the air carrier could constitute a breach of duty only when it is clearly shown that the carrier's employees knew or plainly should have known that the hijacker was unarmed. The general opinion is that the legal oystem could be sufficient, provided that the political will is there to use and apply it effectively. All agreed that the main responsibility for security has to be borne by the governments. A state that supports aviation terrorism is responsible for violation of International Aviation Law. Generally speaking, terrorism is a violation of international law. It violates the sovereign rights of states, and the human rights of the individuals. We have to contribute more to the creation of a general consensus amongst all states about the need to combat the threat of aviation terrorism. I think that aviation terrorism as becoming an ever more serious issue, has to be solved by internationally agreed and closely co - ordinated measures.

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THE EFFECTS OF DRYING AGENTS AND BONDING AGENTS ON THE SHEAR BOND STRENGTH OF SEALANTS TO ENAMEL (치면건조제와 접착제의 사용에 따른 치면열구전색재의 전단결합강도에 관한 연구)

  • Lim, Hyun-Hwa;Jang, Ki-Taek;Kim, Chong-Chul;Hahn, Se-Hyun
    • Journal of the korean academy of Pediatric Dentistry
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    • v.30 no.2
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    • pp.196-203
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    • 2003
  • The application of sealants is a highly technique-sensitive procedure, requiring an extremely dry field prior to placement. Moisture contamination of the etched enamel surface before sealant placement is cited as the main reason for sealant failure. The purpose of this study was to evaluate the effects of different methods of sealant application on the shear bond strength of sealants to enamel. In groups 1, 2, 3, 4 Teethmate(unfilled sealant) was used, while Ultraseal XTplus(filled sealant) was used in groups 5, 6, 7, 8. Groups 1 and 5(control) were acid etched for 15 seconds using 35% phosphoric acid, washed and then dried. In groups 2, 6 drying agents were applied, and in groups 3, 7 bonding agents were applied and light cured. In groups 4 and 8 both drying agent and bonding agent were applied. Then sealant was cured to the specimen using molds 3mm in diameter and 2mm in height. Thermocycling was performed and shear bond strength was finally measured. The following results were obtained : 1. Groups using filled sealant(groups 5, 6, 7, 8) showed higher shear bond strengths compared to groups using unfilled sealant(groups 1, 2, 3, 4). 2. Among groups using unfilled sealant(groups 1, 2, 3, 4), groups 2, 3, 4 showed significantly higher shear bond strength compared to group 1(p<0.05). There were no significant differences among groups 2, 3 and 4. 3. There were no significant differences(p>0.05) among groups using filled sealant(groups 5, 6, 7, 8). 4. When modes of fracture were examined, cohesive failure was observed in groups 2, 3 and 4.

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