• Proceedings of the KSME Conference
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• 2008.11a
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• pp.173-174
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• 2008

The four-point bending test is a widely used method to determine material parameters. The aim of the present study was to evaluate the flexural strength (or modulus of rupture) and the Weibull modulus of cordierite ceramic substrate by means of four-point bending tests. The strength data from experiments followed Weibull statistics. These data indicate that the fatigue effects are more severe when the substrate temperature in the peripheral region is near $200^{\circ}$. At temperatures well above $200^{\circ}C$ the available design strength can be as high as 65% as substrate's initial strength.

• Composites Research
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• v.30 no.1
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• pp.21-25
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• 2017

The aim of this study is to fabricate composite bone plates consisted of unidirectional biodegradable glass fibers (BGF) and polylactic acid (PLA) and evaluate the performance of the composite bone plates according to the temperature ($50.0^{\circ}C$) of PBS (Phosphate Buffer Saline) solution and exposure time (0~3 weeks). Mechanical characteristics, such as bending stiffness, flexural strength, water uptake and mass loss, were investigated and the results showed that mechanical properties of the plates decreased as soaking duration increased due to loss of composite material.

• Journal of Aerospace System Engineering
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• v.4 no.1
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• pp.23-26
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• 2010

In this study, it was performed damage assesment of small scale composite aircraft developing. This aircraft adopted the sandwich structure to skin of wing. This study aims to investigate the residual strength of sandwich composites with Nomex honeycomb core and carbon fiber face sheets after the open hole damage by the experimental investigation. The 4-point bending tests were used to find the bending strength, and the open hole was applied to introduce the simulated damage on the specimen. The bending strength test results after open hole was compared with the results of no damaged specimen test. The FEM analysis is assessed via an experimental 4-point bending test.

• Journal of the Korean Society for Precision Engineering
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• v.31 no.10
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• pp.889-895
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• 2014

Machine parts and structures of a change in the displacement and strain can be evaluated safety is one of the important factors. Typically the strain gauge has been employed to measure the displacement and strain. However, this contact-type measurement method has disadvantages that are not measured under condition of specific object shape, surface roughness and temperature. In particularly, 3 point bending and 4 point bending test not use strain gauge. So its test used cross head displacement and deflect meter. Digital Image Correlation measurement methods have many advantages. It is non contact-type measurement method to measure the object displacements and strain. In addition, it is possible to measure the Map of full field displacements and strain. In this paper, measured the 3 point bending deflection using the Digital Image Correlation methods. In order to secure the reliability, Digital Image Correlation method and universal test machine were compared.

• Journal of dental hygiene science
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• v.15 no.4
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• pp.407-412
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• 2015

This study investigated flexural properties of indirect Gum-shade composite resins for esthetic improvement. The material utilized in this study was Crea.lign, Twiny flow and Twiny paste (TP). Ten specimens were fabricated with a dimension of $25{\times}2{\times}2mm$ according to the ISO 4049. After fabrications, specimens were stored in the distilled water for 24 hours at the temperature of $37^{\circ}C$. Three-point bending test was performed in universal testing machine (Instron 3344; Instron, USA) at a crosshead speed of 1 mm/min until the failure occurred. TP exhibited a higher flexural strength (FS) and flexural modulus (FM) compared to the flowable materials. There were significant differences among the three materials in FS and FM. However, there was no significant difference in work of fracture (WOF) in all tested materials (p>0.05). In Weibull analysis, TP showed the greatest Weibull modulus which means a higher reliability of the materials. Also, Gum-shade composite resins revealed a strong correlation in all flexural properties. There was a positive correlation in FS-FM ($r^2=0.99$) and a negative correlation between FS-WOF and FM-WOF ($r^2>0.97$). Therefore, this confirmed that flexural property was important for mechanical behavior evaluation and useful information. To addition, this improved among mechanical properties correlation of materials as important factor.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.10
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• pp.1541-1550
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• 1997

Since the ceramic/metal joint material is made at a high temperature, the residual stress develops when it is cooled from bonding temperature to room temperature due to remarkable difference of thermal expansion coefficient between ceramic and metal. As residual stress at ceramic/metal joints influences the strength of joints, it is important to estimate residual stress quantitatively. In this study, it is attempted to estimate joint residual stress of Si$_3$N$_4$STS304 joints quantitatively and to compare the strength of joints. The difference of residual stress is measured when repeated thermal cycl is loaded, under the conditions of the practical use of the ceramic/metal joint. The residual stress increases at 1 cycle of thermal load but decreases in 3 cycles to 10 cycles of thermal load. And 4-point bending test is performed to examine the influence of residual stress on fracture strength. As a result, it is known that the stress of joint decreases as the number of thermal cycle increases.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.6 no.1
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• pp.59-68
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• 1997

Recently, the cases of using bonded dissimiliar materials which have each of the different components tend to increase for the purpose of developing new materials and using the special objects in the field of industry. Among the cases the strength evaluation of the joining materials of vehicle engine and the structural materials with ceramic/metal bonded joints becomes more important. But the residual stress occurs, because the joining of ceramics and metals is performed in extremely high temperature. It becomes a dominant cause to reduce the strength of the ceramic/metal bonded joints. In this paper, strength evaluation method of ceramic/metal bonded joints considering stress singularity was investigated by boundary element method and 4-point bending test. An advanced method of quantitative strength evaluation for ceramin/metal bonded joints is to be suggested.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.921-924
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• 2004

This paper is to investigate a crack for plasma sprayed MCrAlY coated material by acoustic emission method in 4-point bending test. The CoNiCrAlY is coated on Inconel-718 by vacuum plasma spray process. Micro-hardness measurement was conducted by means of Micro Vickers-hardness indentor. The porosity of coating layer was measured using a SEM and Image Analyzer. AE monitoring system is composed of PICO type sensor, a wide band preamplifier(40dB), a PC and AE DSP(16/32 PAC) board. The AE count, Hit and energy of coating specimens is measured according to coating thickness.

• Composites Research
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• v.15 no.4
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• pp.32-36
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• 2002

Recently, the applications of composite materials become broader to civil engineering as well as mechanics and aerospace engineering. Cracks on the civil structures like bridges can cause stress concentration, which induces Peak splitting of fiber Bragg grating sensor and it makes strain measurements difficult. In this study, 4-point bending test of concrete beam with initial crack reinforced by composite patch was conducted in order to verify the effects of the stress concentration on the peak signal of FBG sensor and a novel method for signal maintenance.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.4
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• pp.276-284
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• 2000

The acoustic emission (AE) behavior of reinforced concrete beams tested under flexural loading was investigated to characterize and identify the source of damage. This research was aimed at identifying the characteristic AE response associated with micro-crack development, localized crack propagation, corrosion, and debonding of the reinforcing steel. Concrete beams were prepared to isolate the damage mechanisms by using plain, notched-plain, reinforced, and corroded-reinforced specimens. The beams were tested using four-point cyclic step-loading. The AE response was analyzed to obtain key parameters such as the time history of AE events, the total number and rate of AE events, and the characteristic features of the waveform. Initial analysis of the AE signal has shown that a clear difference in the AE response is observed depending on the source of the damage. The Felicity ratio exhibited a correlation with the overall damage level, while the number of AE events during unloading can be an effective criterion to estimate the level of corrosion distress in reinforced concrete structures. Consequently, AE measurement characterization appears to provide a promising approach for estimating the level of deterioration in reinforced concrete structure.