• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.5
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• pp.47-53
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• 2020

The purpose of this study was to increase product reliability by improving the durability of the breech block for a 30mm Automatic Gun. The breech block is a key component of a gun that functions as chambering, closing, and extracting. The breech block requires high reliability, which needs to be improved because cracks of a breech block can occur early in operation. Cause analysis confirmed that the crack is caused by repeated impacts. Therefore, the following improvement measures were studied, and the effects were demonstrated using a firing test. The energy of impact absorption was increased by changing the material, and the stress concentration was mitigated by increasing the value of R. In addition, the fatigue life was increased by adding Shot-peening, deleting chromium plating, and changing the forging method. The firing test did not show firing trouble for up to 5,000 rounds. The start timing of the crack was delayed, and the depth was small. Therefore, the improved product was more durable than the existing product. This study can be used as a useful reference when assessing the improvement of the durability of similar products, life study, and criteria for crack acceptance.

• Journal of the Korea Institute of Military Science and Technology
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• v.14 no.4
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• pp.615-621
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• 2011

In this paper, the proper quantity of conditioning rounds has been studied using the statistical analysis on the basis of the acceptance test data of K676 and K677 propelling charge for K9 self propelled howitzer. In general, the muzzle velocity of the initial rounds tends to be a little lower than that of the succeeding rounds. The latter rounds are likely to have the constant velocities after firing the appropriate conditioning rounds. The main cause of velocity difference was proved to be the proper quantity of conditioning rounds by doing the correlation analysis among the initial tube temperature, the tube life and the quantity of conditioning rounds. The result of paired t-test shows that two rounds of conditioning projectiles are proved to be enough to maintain the constant velocity in the case of the acceptance test of K676 and K677 propelling charge.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.479-483
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• 2005

BBU is the weapon system for the extension of range through the reduction of base drag in 155mm. It has been mass-produced since 2000. The purpose of this research is productivity increase through the reduction of process lead time. Development process is as follows. First, formulation tests about propellent and liner, Second, spin test and final firing test about end products.

• Journal of Korean Society for Quality Management
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• v.45 no.3
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• pp.327-333
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• 2017

Purpose: The purpose of this study is to research to protect to loss of chrome-plating of small arms barrel on high temperature in order to extend its life expectency. Methods: The reason why chrome-plating dropped out is main material is weak from heat. Therfore, to make barrel of small arms have higher heat-resistant property, nitriding for barrel before chrome-plating is needed and test of that barrel was handled to improve it. Results: Nitriding before chrome-plating is useful to protect to chrome-plating loss on high temperature. Conclusion: To protect loss of chome-plating of small arms barrel during on firing, pre-nitriding on barrel is effective finally it leads to extend to barrel's life expectency.

• Tribology and Lubricants
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• v.25 no.3
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• pp.171-175
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• 2009

One of the critical issues associated with the 40mm long hollow cylinder's development and maintenance is the prediction of cylinder erosion. The actual firing test is the most accurate method to measure the cylinder erosion rate. But it costs a great deal and requires a long measurement time. Hence many empirical methods have been proposed to predict the erosion rate and life span of long hollow cylinders. An EFC formula is calculated. An approximate erosion formula for the ammunition type A is derived to interpolate 16 observation values up to 4,000 rounds. A new erosion equation and muzzle velocity formula are also suggested. Several numerical results are presented.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.9
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• pp.291-300
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• 2020

The cartridges used for illuminating a desired point or area are virtually limited in tests and evaluations because of limitations, such as noise during launch, the possibility of fires caused by illuminant charge, and the annual testable quantity. Therefore, to solve these problems, a ground fixed test, which replaces the firing test, or an evaluation method to perform limited tests, can be applied more efficiently. In this paper, the results of an 81mm illuminating cartridge, KM series performed in 2019 were analyzed comprehensively to identify the trends in reliability and quality characteristics and to estimate the shelf life. The shelf life was estimated to be at least 10 years based on the time when the lower confidence level reached 80% at a confidence level of 90%. Considering only major defects, the shelf life can be estimated to be approximately 23 years. On the other hand, the shelf life was estimated to be approximately 11 to 15 years and 25 to 28 years according to the effective illuminating time. Finally, an assessment plan of illuminating cartridges for the mortars was also presented as an improvement plan for an assessment method in the future.

• The Journal of Korean Physical Therapy
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• v.32 no.5
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• pp.295-301
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• 2020

Purpose: The purpose of this study was to compare the electromyographic activity and onset time of the gluteus maximus (GM) and hamstring (HAM), lumbopelvic kinematics during three different prone table hip extension exercises in healthy individuals. Methods: Twenty subjects were participated. Electromyography device was used to measure the muscle activities and onset time of the GM and HAM muscles. An electromagnetic tracking motion device was used to measure lumbopelvic compensations. The subjects were asked to perform three different prone table hip extension [Prone table hip extension with the abdominal drawing-in maneuver on a chair (PTHEA), PTHEA with the ipsilateral knee flexion (PTHEAF), PTHEAF with hip 30 abduction (PTHEAFA)]. One-way repeated measures analysis of the variance and a Bonferroni post hoc test were used. Results: The electromyographic activity and onset time were significantly different among three conditions (PTHEA vs. PTHEAF vs. PTHEAFA)(p<0.01). The GM muscle activity and onset time were significantly greater and reduced during the PTHEAFA compared to PTHEA and PTHEAF (p<0.01). However, The HAM muscle activity and onset time were significantly smaller and delayed during the PTHEAFA compared to PTHEA and PTHEAF (p<0.01). Conclusions: PTHEAFA exercise can be recommended to facilitate the muscle activity and efficient muscle firing time of GM without HAM dominance.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.2
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• pp.468-474
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• 2017

A test service for the weapon systems evaluation is one of the most important processes during the weapon systems acquisition or development life cycle. Before completion of weapon systems development, the appropriate evaluation test can reduce risk and expense which might be expected during weapon systems development procedure. In this paper, it is suggested that a probabilistic prediction method based on Monte Carlo simulation for how much the annual weapon systems evaluation test excution ratio can be reached compared to the yearly initial planned test quantity. And then a weapon systems evaluation test quantitative management scheme is suggested to assist decision making for the test schedule manager who can arrange monthly test schedule based on the prediction result of annual test excution ratio. And the proposed method is applied for the weapon systems evaluation firing test data of the 8th directorate, Agency for Defense Development(ADD). And also the application result is examined.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.20 no.8
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• pp.71-79
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• 2006

For clearing the cause of firing due to the tacking on the surface of phenolic resin, this paper describes the analysis through a couple of methods ; FT-IR; DTA; photograph analysis, etc. Phenolic resin has been widely employed as a case of low voltage appliances. In the experiment it was confirmed that its surface was carbonized and graphitized by the external fire. In the FT-IR test a graphite specimen thermally treated at $150[^{\circ}C]$ showed the 2 different IR absorption peaks at $1,730[cm^{-1}]\;and\;1,680[cm^{-1}]$. In normal phenolic resin, the exothermic peak appeared at $450[^{\circ}C]$, while in graphite specimen, it appeared at $610[^{\circ}C]$ in DTA test. From the results, the electrical fire causes could be cleared and it is expected to protect the human life and property from the electrical fire by using the important data.

• The Journal of Korean Academy of Prosthodontics
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• v.38 no.4
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• pp.446-460
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• 2000

All-ceramic restorations have had a more limited life expectancy than metal ceramic crowns be-cause of their lower strength. The relatively lower strength has limited the use of all-ceramic crowns to the areas where occlusal loads are lower Therefore many researches have been done to increase the strength of all-ceramic crowns. IPS Empress 2 is a new type of lithium disilicate glass-ceramic with enhanced physical characteristics which has been in use clinically since 1998. Previous researches reported that the flexural strength of all-ceramic material was greater than 300 MPa, and all-ceramic crowns can be used in staining or layering technique. The objective of this study was to investigate the influence of the thickness of IPS Empress 2 ceramic on fracture strength. Both staining technique and layering technique was investigated. Vita VMK was used as control. For all three groups, five specimens each of 0.8mm, 1.0mm, 1.4mm, 1.8mm, and 2.2mm thick-ness (a total of 75 specimens) were prepared. Control group : Vita VMK Porcelain specimens were prepared with dentine ceramic and liquid glazing was done. Group I : IPS Empress 2 were prepared with staining technique and stained twice and glazed once. Group II : IPS Empress 2 were prepared with layering technique and glazed after wash firing. The thickness and diameter of the specimen were measured and controlled after specimen preparation. Biaxial Flexure Test (ASTM Standard F394-78) was adopted as this test method produces results least affected by the edge condition of the specimens. Fracture strength was measured with Instron Universal Testing Machine. Conclusions are as follow : 1. The fracture strength was increase in order of control group, test group I, test group II. 2. Fracture strength of the group I (Empress 2 Staining) was 65.54 N in 0.8mm, 155.2 N in 1.0mm, 233.5 N in 1.4mm, 434.5 N in 1.8mm, and 600.1 N in 2.2mm. 3. Fracture strength of the group II (Empress 2 Layering) was 190.0 N in 0.8mm, 283.5 N in 1.0mm. 437.2 N in 1.4mm, 732.0 N in 1.8mm, and 1115.0 N in 2.2mm. 4. No statistical difference was found in flexural strengths according to thickness in a specified group(p>0.05).