• Journal of the Korean Society of Safety
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• v.12 no.2
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• pp.27-36
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• 1997

This paper evaluates the static and fatigue bending strengths of CFRP (carbon fiber reinforced plastic) laminates subjected to hygrothermals. The specimens which had different stacking composition, orthotropic and quasi-isotropic laminated plates, were prepared for this experiment. A steel ball launched by the air gun collides against CFRP laminates to generate impact damages, and the 3-point fatigue bending test is carried out by using the impacted laminates to investigate the influence of hygrothermals on the effect on the residual bending fatigue strength of CFRP laminates.

• Journal of Bio-Environment Control
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• v.27 no.4
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• pp.391-399
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• 2018

In this paper, experimental study performed on steel-pipe connections for structural members of a greenhouse is presented. By those experiments performed, bending moment, deformation and stress distribution of specimens were investigated under four point bending test. The bending performance according to connection method using pin and the stretching is also investigated. The results of bending performance of the no connection specimen were compared to those of other connection specimens. The pin and stretching connection specimens showed lower banding performance than the no connection specimen. The stretching connection method was relatively higher bending performance than the pin connection specimens. According to the results, we proposed the connection method with good bending performance that can be applied to steel-pipe connection in greenhouse.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.483-486
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• 2004

Inner structured and bonded panel, or ISB Panel, as a kind of sandwich type panel, has metallic inner structures which have low relative density, because of their dimensional shape of metal between a pare of metal skin sheets or face sheets. In this work, ISB panels and inner structures formed as repeated pyramidal shapes are introduced. Pyramidal structures are formed easily with expanded metal sheet by the crimping process. Three kinds of pyramidal structures are made and used to fabricate test specimen. Through the multi-point electrical resistance welding, inner structures are bonded with skin sheet. 3-point bending tests are carried out to measure the bending stiffness of ISB panel and experimental results are discussed.

• Journal of Technologic Dentistry
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• v.40 no.1
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• pp.9-15
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• 2018

Purpose: The purpose of this study is to investigate the effect of lithium disilicate glass ceramic polishing on the strength of the final prosthesis. Methods: Fourteen lithium disilicate glass ceramic specimens were prepared. These were randomly divided into two groups of seven(LPG: low polishing group, HPG: high polishing group). In LPG, SiC paper was sequentially polished using 300, 600, 800, 1000 grit, and the specifications of the test piece were adjusted. HPG was sequentially polished using 300, 600, 800, 1000, 1200, 1500, and 2000 grit. Two groups of specimens are executed 3- point bending test. Using the statistical program SPSS 22.0, the average values of the strengths of the two groups were compared in the Mann-Whiteney test. The significance level was set at 0.05. Results: The mean strength value of HPG was measured at $307.14{\pm}23.28MPa$ significantly higher than LPG(p<0.001). Conclusion : The final polishing of the prosthesis is aesthetically important but has proven to play an important role in the flexural strength, early fracture, and prolongation of the prosthesis.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.05a
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• pp.78-82
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• 2001

Impact behaviors of Aluminum Honeycombs Sandwich Panel(AHSP) by drop weight test were investigated. Two types of specimens with 1/2" and 1/4" cell size were tested by two impactors which are weight of $5.25\textrm{kg}_{\textrm{f}}$ and $11.9\textrm{kg}_{\textrm{f}}$. Parametric studies were achieved including the impactor weight and impact sites which consist face, long-edge, short-edge, and point of the specimen. Face one of impact sites was the strongest and short-edge one of impact sites was the weakest. The damaged area of AHSP was enlarged with the increase of impactor weight that is equal to impact energy. After 3 point bending test, fracture modes of AHSP were analyzed with AE counts. Lower facesheet was fractured in the long-edge direction and then separated between facesheet and core. In the short-edge direction after core wrinkled, lower facesheet tear occurred. Impact behavior by FE analysis were increased localized damage in fast velocity because the faster velocity of the impact was, the smaller the stress of core was. Consequently, impactor weight had an effect on widely damaged area, while the impact velocity was caused on the localized damaged area.aged area.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.5
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• pp.415-420
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• 2009

This paper reports the results of a case study for the evaluation of surface damage by using acoustic nonlinearity of surface wave. In this study, the experimental system was constructed to measure the acoustic nonlinear parameter of surface wave in an Aluminum 6061 T6 specimen of which surface was damaged by the three point bending fatigue test, and magnitudes of nonlinear parameter measured before and after the fatigue test were compared. Especially, since the surface fatigue damage by the three point bending is concentrated at the central position of loading, the change in the nonlinear parameter around this position was monitored. Experimental results showed that the measured nonlinear parameter at the outside of this position after the fatigue test was almost same as the initial value before the fatigue test, since the fatigue damage at this position was little. However, clear increase in the nonlinear parameter was noticed after the fatigue test at the central position of specimen where the surface fatigue damage is expected to be concentrated.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1994.03a
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• pp.139-148
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• 1994

An experimental study on material characterization and mechanical properties of SMC(Sheet Molding Compounds) compression molding parts was carried out. Simple compression test using grease oil as a lubricant was carried out to characterize flow stress of SMC at elevated temperatures. Two different mold temperatures, 130$^{\circ}C$ and 150$^{\circ}C$ and two different mold speeds, 15, 45mm/min were used for preparing the specimen of SMC compression molding parts. Surface roughness, tensile, and 3-point bending tests were used to determine the effects of molding temperatures and speeds on mechanical properties of compression molded SMC parts.

• Journal of Biosystems Engineering
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• v.26 no.1
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• pp.47-56
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• 2001

In order to prevent the possibility of mixing of metal powder during food grinding processing with the metal roll mill this study was conducted to develope the materials of ceramics roll as a substitute of gray cast iron mill. Since the ceramics is brittle material and can be broken easily by a crack, it was needed to develope engineering ceramics roll materials with high elastic modulus and fracture toughness. Adding 0∼50 wt% Al$_2$O$_3$as densification additives to porcelain body material and forming the ceramics an different condition, mechanical properties were evaluated. The material structure’s densification process was analyzed by SEM and XRD. The evaluation of the mechanical properties of ceramics roll materials were compared and analyzed by non-destructive test using Young’s modulus and destructive test using 3-point bending strength and fracture toughness. The results showed several correlative results. Porcelain body material with 40 wt% Al$_2$O$_3$content heated at 1,200$\^{C}$ for 5h was high bulk density of 2.77, Young’s modulus of 118.4Gpa, 3-point bending strength of 137 MPa and fracture toughness of 2.88 MPa$.$m$\^$$\sfrac{1}{2}$/ . After analyzing the relationship between non-destructive test and destructive test, the coefficient of determination was more than 0.9. Therefore, the evaluation of non-destructive test by ultrasonic was turned out to be feasible in evaluating the mechanical properties of ceramics.

• Journal of the Optical Society of Korea
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• v.18 no.5
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• pp.523-530
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• 2014

Machine material and structural strain are critical factors for appraising mechanical properties and safety. Particularly in three and four-point bending tests, which appraise the deflection and flexural strain of an object due to external force, measurements are made by the crosshead movement or deflection meter of a universal testing machine. The Digital Image Correlation (DIC) method is one of the non-contact measurement methods. It uses the image analyzing method that compares the reference image with the deformed image for measuring the displacement and strain of the objects caused by external force. Accordingly, the advantage of this method is that the object's surface roughness, shape, and temperature have little influence. However, its disadvantage is that it requires extensive time to compare the reference image with the deformed image for measuring the displacement and strain. In this study, an algorithm is developed for DIC that can improve the speed of image analysis for measuring the deflection and strain of an object caused by a three-point bending load. To implement this algorithm for improving the speed of image analysis, LabVIEW 2010 was used. Furthermore, to evaluate the accuracy of the developed fast correlation algorithm, the deflection of an aluminum specimen under a three-point bending load was measured by using the universal test machine and DIC measurement system.

• Steel and Composite Structures
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• v.46 no.3
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• pp.353-366
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• 2023

This paper presents a finite-element analysis (FEA) of aluminum alloy rectangular hollow sections (RHSs) and square hollow sections (SHSs) with circular through-openings under three-point and four-point bending. First, a finite-element model (FEM) was developed and validated against the corresponding test results available in the literature. Next, using the validated FE models, a parametric study comprising 180 FE models was conducted. The cross-section width-to-thickness ratio (b/t) ranged from 2 to 5, the hole size ratio (d/h) ranged from 0.2 to 0.8 and the quantity of holes (n) ranged from 2 to 6, respectively. Third, results obtained from laboratory test and FEA were compared with current design strengths calculated in accordance with the North American Specifications (NAS), the modified direct strength method (DSM) and the modified Continuous strength method (CSM). The comparison shows that the modified CSM are conservative by 15% on average for aluminum alloy RHSs and SHSs with circular through-openings subject to bending. Finally, a new design equation is proposed based on the modified CSM after being validated with results obtained from laboratory test and FEA. The proposed design equation can provide accurate predictions of flexural capacities for aluminum alloy RHSs and SHSs with circular through-openings.