Experimental Study and Numerical Simulation of G550 High Strength Cold-Formed Steel Z-Section Members Under Pure Bending and Moment Gradient

Jin-you Zhao,Cheng Yu 한국강구조학회 2019 International Journal of Steel Structures Vol.19 No.2

This paper presents a series of bending tests performed on G550 high strength cold-formed steel Z-section members under pure bending and moment gradient. In tests, failure resulted from distortional buckling or the interaction between local and distortional buckling. The test results indicated that the bending strength for moment gradient is greater than that for pure bending. The increasing magnitude is closely bound up with the member’s buckling modes since moment gradient has a signifi cant eff ect on distortional buckling but has a minor eff ect on local buckling. Moreover, fi nite element analysis was applied to verify the tests and the numerical results agree well with test data according to bending strength and failure modes. Furthermore, the test results were compared with the Direct Strength Method (DSM) formulas stipulated in AISI ( 2016) , and it is found that the DSM provides a good agreement with the bending strength for distortional buckling but provides unconservative predictions for the bending strength for interaction between local and distortional buckling.

Application of the full factorial design to modelling of Al₂O₃/SiC particle reinforced al-matrix composites

Necat Altinkok 국제구조공학회 2016 Steel and Composite Structures, An International J Vol.21 No.6

Al₂O₃/SiC particulate reinforced (Metal Matrix Composites) MMCs which were produced by using stir casting process, bending strength and hardening behaviour were obtained using an analysis of variance (ANOVA) technique that uses full factorial design. Factor variables and their ranges were: particle size 2-60 <i>μ</i>m; the stirring speed 450 rpm, 500 rpm and the stirring temperature 620°C, 650°C. An empirical equation was derived from test results to describe the relationship between the test parameters. This model for the tensile strength of the hybrid composite materials with <i>R</i>² adj = 80% for the bending strength <i>R</i>² adj = 89% were generated from the data. The regression coefficients of this model quantify the tensile strength and bending strengths of the effects of each of the factors. The interactions of all three factors do not present significant percentage contributions on the tensile strength and bending strengths of hybrid composite materials. Analysis of the residuals versus was predicted the tensile strength and bending strengths show a normalized distribution and thereby confirms the suitability of this model. Particle size was found to have the strongest influence on the tensile strength and bending strength.

Evaluation of Physical and Mechanical Properties of Non-certificated Laminated Veneer Lumber (LVL) Circulated in Domestic Lumber Market

Sei Chang Oh 한국목재공학회 2011 목재공학 Vol.39 No.5

The selected physical and mechanical properties of non-certificated LVL circulated in domestic lumber market were investigated and compared to relevant standards. The tested LVL passed the moisture content and the soaking delamination rate limit as per domestic (KS) and Japanese standard (JAS). The evaluated mechanical properties were flatwise/edgewise bending strength, modulus of elasticity (MOE), horizontal shear and compressive strength. The 30 mm-thick LVL showed significantly higher bending strength than that of the 25 mm-thick LVL. The modulus of elasticity (MOE) showed same tendency in the results of bending strength. The edgewise bending strength and MOE were higher than that of flatwise bending strength and MOE. The horizontal shear strength values were also showed similar results to bending strength values. The tested results were compared each other and each products were graded according to JAS 701 grade specification. The failure mode of LVL in bending test showed the similar failure mode of solidwood that failed in a simple tension manner (splintery tension). The glue line failure was severe in 25 mm-thick specimens due to concentration of shear stress in layer discontinuity containing small voids and starved glue lines. In horizontal shear strength test, failure mode of LVL showed the typical horizontal shear failure. Compressive specimens failed with fiber crushing in company with apparent delamination that splitted along the length of the specimens. From the results, the complete bonding between lamination and consistency in thin veneer layer were considered as a critical factor in the mechanical properties of LVL. Moreover, the standard test procedure and specification for non-certificated LVL should be required to check the performance of uncertificated materials.

COMPARISON OF MECHANICAL PROPERTIES OF VARIOUS POST AND CORE MATERIALS

Ahn Seung-Geun,Sorensen John A. The Korean Academy of Prosthodonitics 2003 대한치과보철학회지 Vol.41 No.3

Statement of problem: Many kinds of post and core systems are in the market, but there are no clear selection criteria for them. Purpose: The purpose of this study was to compare the flexural strength and modulus of elasticity of core materials, and measure the bending strength of post systems made of a variety of materials. Material and Methods: The flexural strength and elastic modulus of thirteen kinds core buildup materials were measured on beams of specimens of $2.0{\times}2.0{\times}24{\pm}0.1mm$. Ten specimens per group were fabricated and loaded on an lnstron testing machine at a crosshead speed of 0.25mm/min. A test span of 20 mm was used. The failure loads were recorded and flexural strength calculated with the measured dimensions. The elastic modulus was calculated from the slopes of the linear portions of the stress-stram graphs. Also nine kinds commercially available prefabricated posts made of various materials with similar nominal diameters, approximately 1.25mm, were loaded in a three-point bend test until plastic deformation or failure occurred. Ten posts per group were tested and the obtained data were anaylzed with analysis of variance and compared with the Tukey multiple comparison tests. Results: Clearfil Photo Core and Luxacore had flexural strengths approaching amalgam, but its modulus of elasticity was only about 15% of that of amalgam. The strengths of the glass ionomer and resin modified glass ionomer were very low. The heat pressed glass ceramic core had a high elastic modulus but a relatively low flexural strength approximating that of the lower strength composite resin core materials. The stainless steel, zirconia and carbon fiber post exhibited high bending strengths. The glass fiber posts displayed strengths that were approximately half of the higher strength posts. Conclusion: When moderate amounts of coronal tooth structure are to be replaced by a post and core on an anterior tooth, a prefabricated post and high strength, high elastic modulus core may be suitable. CLINICAL IMPLICATIONS In this study several newly introduced post and core systems demonstrated satisfactory physical properties. However when the higher stress situation exists with only a minimal ferrule extension remaining a cast post and core or zirconia post and pressed core are desirable.

이종 접합재의 굽힘 및 인장강도에 미치는 시험편 형상의 효과

허장욱(Jang-Wook Hur) 대한기계학회 2010 大韓機械學會論文集A Vol.34 No.3

이종 접합재(β-Si₃N₄/S45C)의 굽힘강도와 인장강도에 미치는 시험편 형상의 영향을 정량적으로 평가하였다. 평균 굽힘강도와 평균 인장강도는 원형단면 시험편이 4각형 단면 시험편보다 약간 높았다. 또한, 초음파(AE)를 이용하여 균열발생응력을 성공적으로 측정할 수 있었으며, 균열발생응력은 굽힘강도의 60~80% 이었다. 아울러, 세라믹측 접합계면 근처의 잔류응력 측정을 굽힘강도 시험전에 X선 회절법에 의해 실시하였으며, 굽힘강도와 균열발생응력은 잔류응력 증가와 더불어 감소하였다. 마지막으로 인장시험에서 굽힘변형률 성분의 영향을 평가하였으며, 인장강도는 굽힘변형률 성분의 증가와 더불어 감소하고 굽힘강도의 약 80%에 해당되었다. The effect of specimen geometry on the bending and tensile strengths of dissimilar joints (β-Si₃N₄/S45C) with copper interlayers was evaluated. The average bending strength of specimens with circular cross sections was higher than that of specimens with rectangular cross sections. The crack initiation stress (σi) was successfully determined by the acoustic emission (AE) method and was approximately 60~80% of the bending strength. The residual stresses near the interfaces on the ceramic side were measured by X-ray diffraction before conducting the bending test. The bending strength and the crack initiation stress decreased with an increase in the residual stresses. The effect of the bending strain component was evaluated by the tensile testing; the tensile strength decreased with an increase in the bending strain component and was approximately 80% of the bending strength.

Bending fatigue strength of case-carburized helical gears (In the case of large helix angles)

Kengo Nojima,Kengo Ogata,Motomu Tanaka,Ryosuke Nishi,Yuichi Ono,Takao Koide 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.12

Case-carburizing enlarges the depth of the hardened layer at the tooth width end on the acute angle side of helical gears. For the helical gears with large helix angles (Exceeding 25°), this hardened layer may lower their bending fatigue strength. Therefore, we investigated the influence of this hardened layer on their bending fatigue strength through the bending fatigue tests. Our results suggest that this hardened layer might reduce the case-carburizing’s effect to enhance their bending fatigue strength. Thus, using only the maximum tooth root stress would be inadequate for evaluating their bending fatigue strength, and it would be necessary to consider the relationship between the hardened layer and the tooth root stress distribution (Especially, the stress applied at the tooth width end on the acute angle side) from the beginning of meshing to the end.

알루미나 탄화규소 복합세라믹스 균열치유재의 강도와 탄성파 특성

김해숙(Hae Sook Kim),김미경(Mi Kyung Kim),김진욱(Jin Wook Kim),안석환(Seok Hwan Ahn),남기우(Ki Woo Nam) 한국동력기계공학회 2006 한국동력기계공학회 학술대회 논문집 Vol.- No.-

Al₂O₃/SiC Composite Ceramics were sintered to evaluate the bending strength and elastic wave characteristics. The three-point bending test was carried out under room temperature. The elastic wave detected by fracture wave detector. The crack healing behavior was investigated from 1373 K to 1723 K The bending strength of Al₂O₃/SiC composite by nanocomposite is higher than that of Al₂O₃ monolithic. Crack-healing behavior was depended on an amount of additive powder Y₂O₃. In Al₂O₃/SiC composite ceramics with 3 wt. % Y₂O₃ for additive powder, the bending strength at 1573 K is about 100% increase than that of the smooth specimens. From the result of wavelet analysis of elastic wave signal, the smooth specimen and heat treated specimen of Al₂O₃ monolithic and Al₂O₃/SiC composite ceramics showed characteristics of frequency about 58 ㎑. The strength of Al₂O₃/SiC composite ceramics was a little higher than those of Al₂O₃ monolithic. The dominant frequencies were high with increasing of Y₂O₃ for additive powder. The dominant frequencies had direct connection with the bending strength.

CFRP 적층판의 충격손상이 잔류 굽힘 피로강도에 미치는 영향

양용준 ( Yong Jun Yang ),양인영 ( In Young Yang ) 한국안전학회(구 한국산업안전학회) 2015 한국안전학회지 Vol.30 No.3

CFRP composites are used as primary structural members in various industrial fields because their specific strength and specific stiffness are excellent in comparison to conventional metals. Their usage is expanding to high added-value industrial fields because they are more than 50% lighter than metals, and have excellent heat resistance and wear resistance. However, when CFRP composites suffer impact damage, destruction of fiber and interface delamination occur. This causes an unexpected deterioration of strength, and for this reason it is very difficult to ensure the reliability of the excellent mechanical properties. Therefore, for the destruction mechanism in bending with impact damage, this study investigated the reinforcement data regarding various external loads by identifying the consequential strength deterioration. Specimens were damaged by impact with a steel ball propelled by air pressure. Decrease in bending strength caused by the tension and compression of the impact side, and depending on the lamination direction of fiber and interface inside the specimen. From the bending test it was found that the bending strength reduced when the impact energy increased. Especially in the case of compression on the impact side, as tensile stress occurred at the damage starting point, causing rapidfailure and a substantially reduced failure strength.

Bending Strength of Korean Softwood Species for 120 × 180 mm Structural Members

Sung Jun Pang,Joo Saeng Park,Kweon Hwan Hwang,Gi Young Jeong,Moon Jae Park,Jun Jae Lee 한국목재공학회 2011 목재공학 Vol.39 No.5

The goal of this study is to investigate bending properties of domestic timber. Three representative structural timber from Larix kaempferi, Pinus koraiensis, and Pinus densiflora, in the northeastern South Korea were selected. Visual grading for the timber was conducted based on KFRI notification 2009-01 and the bending strength for the timber was evaluated based on ASTM D 198 bending. The high percentage of grade 1 and 2 for Larix kaempferi shows that the KFRI notification was optimized for this species. The bending strength distributions from Pinus koraiensis and Pinus densflora were very similar. It could be possible to specify the allowable bending properties of these two Specification using a united species group similar to spruce-pine-fir. Lastly, the bending strength of 120 × 180 mm structural members was higher than both existing values in KBC 2009 and design values for timber of imported species described in the NDS. Thus, 120 mm thick domestic sofiwoods could replace the commercial imported species and the KBC should be modified to provide design values for both timber and dimensional lumber, respectively, like NDS.

Bending fatigue strength of case-carburized helical gears with large helix angles up to 40 degrees

Mikiya Yamaoka,Motomu Tanaka,Masaya Kumada,Kengo Nojima,Ryosuke Nishi,Yuichi Ono,Takao Koide 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.12

Case-carburizing of helical gears with large helix angles may form too large hardened layers near the tooth width end on the acute angle side (ACUTE-END), and adversely affect the bending fatigue strength. We investigated the bending fatigue strength of casecarburized helical gears with large helix angles up to approximately 40° through a bending fatigue test, hardness test, and residual stress measurement. We found that the case-carburizing formed large hardened layers near ACUTE-END, reduced the compressive residual stress near ACUTE-END, and restricted the improvement of the bending fatigue strength in a meshing state where tooth root stress became large near ACUTE-END. Based on the obtained bending fatigue limits, we revealed that ISO 6336-3:2006 overestimated the rate of increase of the permissible circumferential loads for helix angles exceeding approximately 30°, and ISO/DIS 6336-3:2018 underestimated this rate for helix angles near 30°.