• Advances in nano research
• /
• 제14권4호
• /
• pp.363-373
• /
• 2023

A novel type of steel fiber with a rounded-end shape is presented to improve the bonding behavior of fibers with Carbon Nanotubes (CNT)-reinforced Ultra-High Performance Concrete (UHPC) matrix. For this purpose, by performing a parametric study and using the nonlinear finite element method, the impact of geometric characteristics of the fiber end on its bonding behavior with UHPC has been studied. The cohesive zone model investigates the interface between the fibers and the cement matrix. The mechanical properties of the cohesive zone model are determined by calibrating the finite element results and the experimental fiber pull-out test. Also, the results are evaluated with the straight steel fibers outcomes. Using the novel presented fibers, the bond strength has significantly improved compared to the straight steel fibers. The new proposed fibers increase bond strength by 1.1 times for the same diameter of fibers. By creating fillet at the contact area between the rounded end and the fiber, bond strength is significantly improved, the maximum fiber capacity is reachable, and the pull-out occurs in the form of fracture and tearing of the fibers, which is the most desirable bonding mode for fibers. This also improves the energy absorbed by the fibers and is 4.4 times more than the corresponding straight fibers.

• 대한기계학회논문집A
• /
• 제41권7호
• /
• pp.635-643
• /
• 2017

STS 304L 강재의 냉간압연율의 증가에 따라 t가 1.5 mm에서 1.1 mm까지 감소하면 인장강도, 항복강도, 경도치 및 UFT피로시험의 피로한도는 선형적으로 증가하였다. t=1.5 mm, t=1.4 mm, t=1.3 mm 및 t=1.1 mm인 4가지 시험편의 UFT피로시험(R= -1)결과, 회전굽힘피로시험(R= -1)의 결과처럼 $10^6$ 영역에서 S-N곡선의 피로한도가 절점(knee point)을 형성하였고, 기가사이클 피로에서 생기는 현상인 피로한도가 추가로 감소하지않았다. 또 t=1.1 mm인 경우 가장 높은 피로한도 345 MPa로 되었고, 원소재(t=1.5 mm)에 대하여 64.3 % 증가하였다. 냉간압연율에 따른 UFT피로시험결과 많은 작은 표면균열이 티어링(tearing)하면서 발생, 성장, 서로 합체하였다.

• Journal of the Korean Wood Science and Technology
• /
• 제19권3호
• /
• pp.62-71
• /
• 1991

An evaluation of bending test of composite I and Box beams for determining the ultimate strength limit design criteria was presented. Maxium loads of composite I beams were found in beams composed of thicker upper flanges and/or vertical LVL flanges. These loads of plywood web beams were greater than those of PB web beams. Maximum loads of unsymmetrical box beams were less than those of symmetrical box beams. Thus, it took on different phase in box type beams. Ultimate loads of composite beams were greater than those of solid. The failure of composite beams were abrupt and failure mode was classified into following categories; Edgewise shear failure in web, delamination in flange-web joint, tension failure and tearing in LVL flanges, and web delamination. These failures of composite beams were appeared at the mixed mode. The influence factor affecting the performance of tested composite beams was shear strength of PB-web composite beams and compressive strength in plywood-web composite beams. It was also assumed that the influence factors on structural performance on composite beams were flange quality, web material and geometry of cross section. As one of the design methods resisting to compressive stress that was required in the case of small span to depth ratio and deep beams. composite I-beams composed of thicker upper flanges comparing to lower flanges were very effective in structural performance.

• 한국해양공학회지
• /
• 제28권1호
• /
• pp.28-33
• /
• 2014

The Korean icebreaking research vessel "Araon" performed four sea trials in the Arctic and Antarctic Seas. The ice properties, such as the ice thickness, floe size, ice strength, and power of the vessel were quite different in these trials. To compare the speeds of ship with the same ice strength and power, the AARC (Arker Arctic Research Center) method is used with a vessel power of 10 MW and an ice strength of 630 Pa in this paper. Based on the analysis results, the speed of the ship was 1.62 knots (0.83 m/s) with a 1.02-m ice thickness and 2.5-km floe size, 5.3 knots (2.73 m/s) with a 1.2-m ice thickness and 1.0-km floe size, and 13.8 knots (7.10 m/s) with a 1.1-m ice thickness and 200-m floe size. The analysis results showed that the ship speed and floe size have an inversely proportional relationship. Two reasonable reasons are given in this paper for the final result. One is an ice breaking phenomenon, and the other is the effect of the ice floe mass. For the breaking phenomenon, the ice breaking force is very small because the ice floe is not breaking but tearing when a ship is passing through a small ice floe. Regarding the effect of the ice floe mass, it is impossible for a ship to push and tear an ice floe if the mass of the ice floe is too large compared to the mass of the ship. The velocity of the ship decreases when the ice floe has a large mass and a large size because the ship has to break the ice floe to move forward.

• 한국식품영양과학회지
• /
• 제34권2호
• /
• pp.298-305
• /
• 2005

과채류 포장용 기능성 항균포장지는 항균력이 우수한 식물성 항균소재(botanical antimicrobial agent-grapefruit seed extract mixture: BAAG)의 CaCO$_3$분말제재와 가스흡착제 기능을 소유한 제올라이트를 일정배합비율로 펄프지료에 첨가하여 TAPPI Standard Method T200 sp-96에 의거하여 제조하였다. 아울러, 보류향상제인 cationlc polyacrylamide (Ca-PAM)와 발수처리제 alkyl ketone dimer(AKD)도 같이 첨가하였다. 이때, 사용된 BAAG분말의 평균입자크기는 12.45였으며, Scanning Electron Microscope 촬영사진에서 CaCO$_3$에 침착되어 있는 BAAG 및 제올라이트가 육면체 형태의 미세한 분말로 지료상에 구성되어 있음을 알 수 있었으며, 포장원지내에 보류된 항균제의 보유량을 회분함량으로 측정한 결과, 항균제의 첨가량을 증가시킬수록 회분함량이 증가하는 것으로 미루어 Ca-PAM이 지료 섬유 네트워크내에 항균제를 정착시키는데 매우 효과적인 보류향상제로 작용함을 알 수 있었다. 한편, 분말형 항균제와 제올라이트를 지료에 첨가하여 포장원지를 제조하였을 때, 포장원지의 인장강도(tensile strength)와 파열강도(burst strength)는 항균제와 제올라이트를 첨가하지 않았을 때보다 다소 감소하는 경향을 나타내었고, 반면에 강성(stiffness)과 인열강도(tear strength)는 증가하는 경향을 나타내었다. 그러나, 기능성 첨가제 분말의 첨가로 인하여 발생할 수 있는 골판지 상자의 라이너나 단위 포장용(itempackaging)포장지의 강도적 성질의 감소현상이 미미할 것으로 판단되어 항균포장지 제조에 사용되는 항균제와 제올라이트분말은 종이의 물성 열화에 미치는 영향이 크지 않는 것으로 나타났다.

• 산업기술연구
• /
• 제36권
• /
• pp.39-43
• /
• 2016

The purpose of this study is to determine and compare the mechanical and flow properties of polyvinylsiloxane impression pastes. Twelve polyvinylsiloxane impression materials were used. As mechanical properties, tensile strength and tear resistance were measured. Impression materials are subjected to tensile stresses when they are removed from the oral cavity and from stone models and tear resistance is the ability of the material to resist tearing under a tensile stress. Flow is dependent on the ability of the material to resist shear forces. Flow tests were performed to determine the handling characteristics and was measured using a shark fin testing device. An impression material must be able to penetrate the narrow subgingival sulcus and tight interproximal areas. Therefore, it must be able to resist the shear forces as it is pushed between tooth and gingival walls. It is necessary to understand the properties of interocclusal recording materials and is considered that the results obtained in this study will provide guideline information for the manufacturing of impression materials and for selecting appropriate impression materials.

• Journal of Welding and Joining
• /
• 제4권1호
• /
• pp.47-57
• /
• 1986

The elastic-plastic fracture toughness J_{Ic}$ of submerged arc welded structural steel $SB_{41}$ which has the properties of low strength and high ductility was discussed, especially paying attention to a comparison between two methods recommended by ASTM and JSME. $J_{IC}$ tests were carried out with compact specimens by means of R-curve, SZW, ultrasonic and electric potential methods. Based on the investigations in this study, the results obtained are as follows; (1) The JSME R-curve method gave the smallest $J_{IC}$ values which were physically closest to the crack initiation and seemed to be more practical and stable procedure between the two R-curve methods. (2) The JSME SZW method tended to slightly overestimate the $J_{IC}$ values at initiation of ductile tearing. (3) The ultrasonic and electric potential methods which also had a tendency to overestimate these $J_{IC}$ values were confirmed to be applicable and useful in determining these values. (4) The $J_{IC}$ values by the JSME R-curve method were 18.06 kgf/mm and 17.25kgf/ mm for the smooths and the side grooved CT specimen respectively.

• 한국펄프종이공학회:학술대회논문집
• /
• 한국펄프종이공학회 2010년도 춘계학술발표회 논문집
• /
• pp.195-206
• /
• 2010

Xylan can be applied to improve the strength properties of paper; however the optical properties, such as brightness, are decreased significantly. To solve that problem, an applicable bleaching process is therefore desired. The aim of this research was to investigate the impact of hydrogen peroxide bleaching on hardwood kraft pulp pretreated with birchwood xylan by measuring optical properties (whiteness, brightness, opacity) as well as physical properties (tensile index, tearing index, bulk) of handsheets made from the bleached pulp. Hydrogen peroxide bleaching, as a kind of totally chlorine free (TCF) bleaching method, is quite important industrially for chemical pulp. In our work, the process variables of peroxide bleaching including bleaching temperature, time, initial pH and $MgSO_4$ dosage were studied. The results showed that both good mechanical properties and optical properties could be achieved when the operating parameters were controlled properly and therefore hydrogen peroxide bleaching was proved to be a suitable method for bleaching hardwood kraft pulp with adsorption of birchwood xylan.

• 한국응용과학기술학회지
• /
• 제13권3호
• /
• pp.137-144
• /
• 1996

Durable softening water repellents such as PODCW, PDDCW, and PEDCW were prepared by blending cationized polymers, fatty carbamide, waxes, and emulsifiers. The cationized polymers included poly (octadecyl methacrylate-co-2-diethylaminoethyl methacrylate) [PODC], poly (n-dodecyl methacrylate-co-2-diethylaminoethyl methacrylate) [PDDC]and poly (2-ethylhexyl methacrylate-co-2-diethylaminoethyl methacrylate) [PEDC]. After the PET fabrics were treated with these water repellents, water repellency, softness, and durability of the PET fabrics were examined by various methods : water repellency by the hydrostatic pressure and the contact angle methods, softness by crease recovery and tearing strength, and durability by washability, respectively. Rating of water repellency of PET fabrics treated with PODCW was $80^{+}$, but those treated with PDDCW and PEDCW were not high enough to be used in industry.

• 한국공간구조학회:학술대회논문집
• /
• 한국공간구조학회 2008년도 춘계 학술발표회 논문집
• /
• pp.31-36
• /
• 2008

건축용 막재는 자유로운 형태와 가벼움 때문에 전 세계적으로 대공간 구조물에 많이 사용되어 왔다. 건축용 막재가 바람이나 눈하중에 의해서 하중 조건하에서 구조적 문제를 발생하여 막재가 파손되는 경우가 발생하였다. 본 논문에서는 유리섬유 막재는 대한 1축인장시험 및 반복하중 시험을 수행하여 응력 변형도 곡선을 분석하고자 한다. 반복하중 시험에서 얻은 응력 변형도 곡선에서 유리섬유 막재는 반복하중이 작용할 시에 인장강도 이하에서 파단한다는 것을 알 수 있고, 폴리에스터 막재는 반복하중에 의해서 변위가 점차적으로 증가한다는 것을 보여주었다.