• Tribology and Lubricants
• /
• v.35 no.4
• /
• pp.222-228
• /
• 2019

As rubber products such as O-rings, which are also known as packings or toric joints, come in regular, long term contact with liquid fuel, they can eventually swell, become mechanically weakened, and occasionally crack; this diminishes both their usefulness and intrinsic lifetime and could cause leaks during the steady-state flow condition of the fuel. In this study, we evaluate the lifetime of such products through compression set tests of FKM, a family of fluorocarbon elastomer materials defined by the ASTM international standard D141; these materials have great compression, sunlight, and ozone resistance as well as a low gas absorption rate. In this process, O-rings are immersed in the liquid fuel of airtight containers that can be expressed as a compression set, and the liquid fuel leakage in a flow rig tester at variable temperatures over 12 months is investigated. Using the Power Law model, our study determined a theoretical O-ring lifetime of 2,647 years, i.e. a semi-permanent lifespan, by confirming the absence of liquid fuel leakage around the O-ring assembled fittings. These results indicate that the FKM O-rings are significantly compatible for fuel tests to evaluate long-term sealing conditions.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.8 no.2
• /
• pp.111-118
• /
• 1984

On the basis of plasticity theory for porous metal, an analysis of ring compression is carried out, employing the upper bound approach. The plastic flowability and the neutral radius of porous metal ring are calculated and deformation characteristics of power forging are obtained from this result. The experiments on ring compression are carried out for sintered iron porous metal with various relative densities under various friction conditions. A good agreement is observed between the shapes of the calculated curves and the experimental results from the ring compression test. The friction factor for powder metal forming can be determined not only from the relationship between reduction in height and reduction in internal diameter but independently from the relationship between reduction in height and relative density, if the initial relative density is known.

• Tunnel and Underground Space
• /
• v.7 no.3
• /
• pp.221-229
• /
• 1997

Disc-type and ring-type specimens of four different materials were tested to investigate the tensile characteristics and their brief results are presented. Materials tested were marble, granite, cement mortar and plaster. Unizxial tensile strengths are compared with Brazilian and ring test strengths. It was found that Brazilian strengths were usually greater than uniaxial tensile strengths and affected by loading rates. In the ring tests, tensile strengths were generally found to be decreased as relative hole radius being increased. Ring test strengths, however, converged to some value in r$\geq$0.45 of marble, r$\geqq$0.29 of cement mortar and r$\leq$0.5 of plaster specimens. In such range of r, furthermore, transverse cracking of specimens were observed.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2003.10b
• /
• pp.31-35
• /
• 2003

Friction in cold forging with mist lubrication is measured with the ring compression test. Small quantity of mist lubricant is sprayed onto the surfaces of cemented tungsten carbide (WC) tools polished to mirror surfaces, and the specimens of pure aluminum are compressed. It is found that spraying small quantity of lubricant $(0.5\;g/m^2)$ is effective to reduce the friction in comparison with the dry condition. The mist particles stick to the tool surface as separated dots, and the behavior of the trapped mist lubricant between the tool and specimen during upsetting is discussed.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.22 no.3
• /
• pp.483-492
• /
• 1998

An inverse analysis been applied to obtain the flow stress of the material. In this method, a ring-shaped specimen is compressed between two flat tools. This procedure employs, as the object function of inverse analysis, the balance of measured loads and reaction forces calculated by using rigid-plastic finite element method. The balance is explicit scalar function of flow stress which is a function of some unknown constants. For minimizing the balance, Newton-Raphon scheme is used. The friction factor, m, between flat tools and the specimen is determined by using friction area-divided method. The proposed method allows an accurate identification by avoiding the usual assumptions made in order to convert experimental measures into stress-strain relation. In this paper, the proposed method is numerically tested. A commercial pure aluminum was selected, as an example, to apply the method and the results are compared with stress-strain relation obtained by experiments.

• Journal of Korea Technical Association of The Pulp and Paper Industry
• /
• v.31 no.3
• /
• pp.47-53
• /
• 1999

The effect of coating of liner components with oxidized starch on the properties of corrugated box was examined . Coating was carried out on liner components of B flute, single-wall corrugated board(SK180/S120/K200) , and corrugated box was made from the treated corrugated board. Box was made in a regular slotted container (RSC) style, and box compression strength was determined in the direction of top-to-bottom compression. The compression strength of box coated on outside liner component showed 15.4% improvement for 1.58g㎡ coating. On the other hand, the strength of box coated on outside liner component showed only 1.45% improvement for 1.41g/㎡ coating and 3.46% improvement for 2.32g/㎡ coating. Coating on inside liner component with oxidized starch at low coating weight more significantly improved box compression strength than coating on outside liner component, and the improvement was marked at the coating weight of 1.5-2.5g/㎡. In estimating top-to-bottom box compression strength, the experimental values were closer to the calculated values from McKee's equation suing edgewise compression strength of the combined board measured by column crush test than those from Kellicutt's equation using compression strength of component paperboards measured by ring crush test.

• Transactions of Materials Processing
• /
• v.29 no.5
• /
• pp.257-264
• /
• 2020

This paper is concerned with the influence of the plastic property of the rivet on the numerical prediction of the Self-Piercing Rivet (SPR) Joining. In order to predict the plastic property of the rivet, a ring compression specimen was directly fabricated from the rivet used for the mechanical joining of dissimilar materials, and the FE analysis together with the ring compression test was iteratively carried out by changing the plastic property of the rivet. For reliable FE analysis, a friction coefficient was estimated based on a friction calibration curve, measuring the reductions in inner diameter and height of the ring specimen after the compression test. From each simulation result, the force-displacement curves were then compared from each other so as to obtain the rivet plastic property that shows good agreement with the experimental result. The SPR joining between GA590 1.0t and Al5052 2.0t was conducted, and the numerical prediction was performed with the use of the plastic property evaluated based on the inverse analysis and the one referred from Mori et al. [11]. Comparison of the experiment and the numerical predictions in terms of the interlock and bottom thickness revealed that the reliable evaluation of the plastic property of the rivet is necessary for the trustworthy numerical prediction of the SPR joining.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.34 no.10
• /
• pp.1471-1478
• /
• 2010

Microforming processes have recently attracted considerable attention from industry and academia since they enable the production of microscale parts using various materials at a high production rate, minimize material loss, and provide parts with excellent mechanical properties. However, for successful development and applications of the microforming process it is critical to take the tribological size effect into consideration because previous studies have shown that traditional friction models for macroscale forming generate significantly erroneous results in the case of microforming. In this paper, we performed scaled ring compression experiments to investigate the tribological size effect of aluminum and brass materials in microforming. The sensitivity of the interfacial friction to the deformation characteristics of the ring was quantitatively analyzed by the finite element analysis. In addition, a friction model based on slip line field and upper boundary techniques was used to theoretically explain the friction mechanism in microforming.

• Transactions of Materials Processing
• /
• v.21 no.1
• /
• pp.13-18
• /
• 2012

During warm forging, materials are formed in the temperature range of $300^{\circ}C\sim900^{\circ}C$. In this temperature range, the friction between the forging die and the material is very high and has a negative effect on the forming process causing severe die wear and possible defects in the component because of stick-slip. Thus, lubrication characteristics are a very important factor for productivity during warm forging. In this paper, ring compression experiments were conducted to estimate the friction factor between the die and the materials as the main factor in characterizing the lubricant. Also, ring tests using normal graphite power as a lubricant coating system were compared with tests using nano graphite powder. The results confirm that the nano graphite is superior to the normal graphite in view of its lubricating effect. In addition, the friction factor (m) was estimated with respect to the amount of the nano graphite content in the lubricant. With 10 % nano graphite the friction factor had the lowest value as compared to other amounts. It can be concluded that the amount of the nano graphite in the coating system can be optimized to obtain the best lubrication condition between the die and the material using ring test experiments.

• Structural Engineering and Mechanics
• /
• v.73 no.6
• /
• pp.613-620
• /
• 2020

The research study is focuses on a form of all-bolted joint with the external ring stiffening plate in the prefabricated steel structure. The components are bolted at site after being fabricated in the factory. Six specimens were tested under cyclic loading, and the effects of column axial compression ratio, concrete-filled column, beam flange sub plate, beam web angle cleats, and spliced column on the failure mode, hysteretic behavior and ductility of the joints were analyzed. The results shown that the proposed all-bolted joint with external ring stiffening plate performed high bearing capability, stable inflexibility degradation, high ductility and plump hysteretic curve. The primary failure modes were bucking at beam end, cracking at the variable section of the external ring stiffening plate, and finally welds fracturing between external ring stiffening plate and column wall. The bearing capability of the joints reduced with the axial compression ratio increased. The use of concrete-filled steel tube column can increase the bearing capability of joints. The existence of the beam flange sub plate, and beam web angle cleat improves the energy dissipation, ductility, bearing capacity and original rigidity of the joint, but also increase the stress concentration at the variable section of the external reinforcing ring plate. The proposed joints with spliced column also performed desirable integrity, large bearing capacity, initial stiffness and energy dissipation capacity for engineering application by reasonable design.