• Korean Journal of Metals and Materials
• /
• v.48 no.3
• /
• pp.203-209
• /
• 2010

An application of the instrumented indentation technique has been expanded from the measurements of hardness and elastic modulus to the analysis of residual stress. A slope of the indentation loading curve increases (or decreases) according to compressive (or tensile) residual stress. A theoretical equation has been established for quantifying residual stress from the slope change. However, a precise observation of the remnant indents is indispensible because the theoretical approach needs actual contact information. In addition, the conventional hardness test is still used for predicting the residual stress distribution of welded joints. Thus, we observed the three-dimensional morphologies of the remnant indents formed on artificial stress states and analyzed stress effects on morphological recovery of the indents. First, a depth recovery ratio, which has been regarded as a sensitive stress indicator, did not show a clear dependency with the residual stress. Thus an analysis on volumetric recovery was tried in this study and yielded a inverse proportional behavior with the residual stress. In addition, an elastic to plastic volume recovery ratio showed more significant correlation with the residual stress.

• Journal of Yeungnam Medical Science
• /
• v.38 no.3
• /
• pp.258-263
• /
• 2021

Neurolymphomatosis (NL) is defined as the involvement of the peripheral nervous system in lymphocytic invasion. It is a very rare form of lymphoma that may occur as an initial presentation or recurrence. It affects various peripheral nervous structures and can therefore mimic disc-related nerve root pathology or compressive mononeuropathy. NL often occurs in malignant B-cell non-Hodgkin lymphomas. Notwithstanding its aggressiveness or intractability, NL should be discriminated from other neurologic complications of lymphoma. Herein, we present a case of primary NL as the initial presentation of diffuse large B-cell lymphoma (DLBCL) of the sciatic nerve. The patient presented with weakness and pain in his left leg but had no obvious lesion explaining the neurologic deficit on initial lumbosacral and knee magnetic resonance imaging (MRI). NL of the left sciatic nerve at the greater sciatic foramen was diagnosed based on subsequent hip MRI, electrodiagnostic test, positron emission tomography/computed tomography, and nerve biopsy findings. Leg weakness slightly improved after chemotherapy and radiotherapy. We report a case wherein NL, a rare cause of leg weakness, manifested as the initial presentation of primary DLBCL involving the sciatic nerve at the greater sciatic foramen.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.49 no.7
• /
• pp.549-555
• /
• 2021

Open hole strength of composite laminates is often used as the design allowable strength for designing composite aircraft structures, particularly those structures subjected to impact loading. Generally, the degradation of strength due to a barely visible impact damage (BVID) is assumed as the strength of 6.0 mm hole diameter in 24.0 mm width specimen. In this study, the residual strength static tests of composite laminates containing circular holes have been performed to investigate the effects of fiber orientation structure on open hole strength. The point stress criterion using a characteristic length is used to predict the open hole strength. The finite element analysis has been used to validate the analytical method. From the test results, it is shown that the characteristic length is related to the percentage of 0°, ±45° and 90° plies of the laminate. And regression analysis has performed to determine the characteristic length and strength of no hole specimens on the arbitrary layup pattern.

• Computers and Concrete
• /
• v.27 no.3
• /
• pp.241-252
• /
• 2021

An experimental program was conducted to investigate the fresh properties, mechanical properties and durability characteristics of the self-compacting mortars (SCM) produced with pumice powder and Artificial Lightweight Fine Aggregate (aLWFA). aLWFA was produced by using fly ash. A total of 16 different mixtures were designed with a constant water-binder ratio of 0.37, in which natural sands were partially replaced with aLWFA and pumice powder at different volume fractions of 5%, 10% and 15%. The artificial lightweight aggregates used in this study were manufactured through cold bonding pelletisation of 90% of class-F fly ash and 10% of Portland cement in a tilted pan with an ambient temperature and moisture content. Flowability tests were conducted on the fresh mortar mixtures beforehand, to determine the self-compacting characteristics on the basis of EFNARC. To determine the conformity of the fresh mortar characteristics with the standards, mini-slump and mini-V-funnel tests were carried out. Hardened state tests were conducted after 7, 28 and 56 days to determine the flexural strength and axial compressive strength respectively. Durability, sorptivity, permeability and density tests were conducted at the end of 28 days of curing time. The test results showed that the pumice powder replacement improved both the fresh state and the hardened state characteristics of the mortar and the optimum mixture ratio was determined as 15%, considering other studies in the literature. In the aLWFA mixtures used, the mechanical and durability characteristics of the modified compositions were very close to the control mixture. It is concluded in this study that mixtures with pumice powder replacement eliminated the negative effects of the aLWFA in the mortars and made a positive contribution.

• Journal of the Korea Institute of Building Construction
• /
• v.21 no.1
• /
• pp.21-29
• /
• 2021

The objective of this study is to evaluate the effect of the application of double layered bubble sheet on the curing of slab and wall concrete placed at the job site in cold weather and to offer a feasibility of Concrete IoT Management System(CIMS), which is wireless sensor network developed by the authors, to manage early age quality of the concrete in terms of temperature, maturity and strength development. Test results indicated that the application of bubble sheet enhances the insulation performance, which results in an increase of the temperature by around 1~20. 6℃. It is found that CIMS can gather the temperature, maturity and strength development data from the sensors embedded from 30 m far from CIMS successfully. Predicted compressive strengths by CIMS had good agreement with measured ones within 2 MPa error level until 7 days. It is thought that the combination of the bubble sheet application for cold weather protection and CIMS for quality management tool in cold weather concreting contributes to shorten the time for the form removal by one day.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.10 no.3
• /
• pp.321-326
• /
• 2022

In this study, cogeneration power plants that use biomass as a raw material to convert them into energy have recently received a lot of attention worldwide and are gradually increasing in South Korea. Therefore, in order to confirm the possibility of using the generated floor material as a fine aggregate for concrete, properties and stability evaluation experiments were performed. Compared to standard sand, the compressive strength of wood chip aggregate was improved by 11 % to 111 %, the length change rate was 89 %, and the waste processing test results met all criteria for hazardous substances. All of these are satisfied, and it is judged that the floor materials by the cogeneration power plant can be used as a fine aggregate for concrete.

• Journal of the Korean Geosynthetics Society
• /
• v.21 no.3
• /
• pp.29-39
• /
• 2022

The engineering characteristics of synthetic polymer-silica sol, which has the effect of reducing leakage, was evaluate and compared with typical grouting material, the water glass-based SGR injection material in this study. The result of the laboratory tests on strength and durability about the synthetic polymer-silica sol showed more than twice as high as LW-based injection materials in uniaxial compressive strength, significantly lower values in shrinkage rate and permeability. The result of pH was less than 8.5 (the drinking water quality standard). As a result of the leaching test, the Na₂O elution amount of the synthetic polymer-silica sol was measured to be 3 to 4 times smaller than that of the water glass grout. These results be assumed that the synthetic polymer-silica sol has better durability and permeability than those of the typical water glass-based grout.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.10 no.3
• /
• pp.243-251
• /
• 2022

The purpose of this study is to investigate experimentally the effect of polyethylene fibers with different tensile strength and aspect ratio on the properties of cementless composite. Three types of mixtures according to the types of polyethylene fibers and water-to-binder ratio were prepared and density, compressive strength and tension tests were performed. Test results showed that the mixture reinforced by polyethylene fiber with a low tensile strength by 10 % and a high aspect ratio by 8.3 % had a high tensile strain capacity by 11.7 %, a high toughness by 12.4 %, and a low crack width by 9.1 %. It was also observed that high tensile strain capacity and better cracking pattern could be achieved by increasing the water-to-binder ratio of composite although its strength is low.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.25 no.4
• /
• pp.37-45
• /
• 2021

This paper is a basic study to evaluate the possibility of earthquake-resistant reinforcement by reinforcing engineered cementitious composite in masonry members. In order to examine the performance according to the fiber mixing rate of the engineered cementitious composite, a test specimen was prepared according to the formulation design, and flow ability, compressive strength, flexural strength, length change rate, and direct tensile strain were measured. In addition, non-reinforced masonry members, masonry members reinforced with engineered cementitious composite, and masonry members in which glass fibers and wire mesh were separately reinforced with engineered cementitious composites were manufactured, and flexural strength and maximum displacement were measured. All specimens reinforced with engineered cementitious composite showed more than 16 times the effect of maximal strength compared to that of no reinforcement, and as a result of examining the crack shape, the energy dissipation ability was excellent, confirming the possibility of seismic reinforcement.

• KSII Transactions on Internet and Information Systems (TIIS)
• /
• v.16 no.4
• /
• pp.1224-1248
• /
• 2022

In various sensor network applications, such as climate observation organizations, sensor nodes need to collect information from time to time and pass it on to the recipient of information through multiple bounces. According to field tests, this information corresponds to most of the energy use of the sensor hub. Decreasing the measurement of information transmission in sensor networks becomes an important issue.Compression sensing (CS) can reduce the amount of information delivered to the network and reduce traffic load. However, the total number of classification of information delivered using pure CS is still enormous. The hybrid technique for utilizing CS was proposed to diminish the quantity of transmissions in sensor networks.Further the energy productivity is a test task for the sensor nodes. However, in previous studies, a clustering approach using hybrid CS for a sensor network and an explanatory model was used to investigate the relationship between beam size and number of transmissions of hybrid CS technology. It uses efficient data integration techniques for large networks, but leads to clone attacks or attacks. Here, a new algorithm called SBEA (Snowball Endurance Algorithm) was proposed and tested with a bow. Thus, you can extend the battery life of your WSN by running effective copy detection. Often, multiple nodes, called observers, are selected to verify the reliability of the nodes within the network. Personal data from the source centre (e.g. personality and geographical data) is provided to the observer at the optional witness stage. The trust and reputation system is used to find the reliability of data aggregation across the cluster head and cluster nodes. It is also possible to obtain a mechanism to perform sleep and standby procedures to improve the life of the sensor node. The sniffers have been implemented to monitor the energy of the sensor nodes periodically in the sink. The proposed algorithm SBEA (Snowball Endurance Algorithm) is a combination of ERCD protocol and a combined mobility and routing algorithm that can identify the cluster head and adjacent cluster head nodes.This algorithm is used to yield the network life time and the performance of the sensor nodes can be increased.