• Magazine of the Korean Society of Agricultural Engineers
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• v.41 no.1
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• pp.97-105
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• 1999

Recently , polymer concrete has been widely used in the construction industry because of its quick setting, high strength, excellect adhesion, watertightness and chemical resistance compared to ordinary cement concrete. Its application is also increased. In this paper, lightweight polymer mortars using unsaturated polyester resin and lightweight aggregate are prepared with various mix proportations, and tested for slump working life, apparent specific gravity , flexural and compressive strengths. As a result, the slump and working life can be controlled and thier flexural and compressive strengths are 9.7 to 22.0 MPa , and 23.0 to 100.8 MPa respectively at apparent specific gravities of 0.86 to 1.73.

• The Journal of Korean Academy of Prosthodontics
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• v.35 no.3
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• pp.517-534
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• 1997

It has been held that excessive mechanical forces to the osseous and soft tissues of the TMJ result in joint dysfunction. Understanding the stress pattern on TMJ is very important in TMJ research. But, it is very difficult to measure directly the biomechanical stress distribution in the TMJ when the mandible is loaded. Therefore, stress distribution in the TMJ during functional movement was studied through animal experiment or mathematical model. It was observed and compared the stress distribution occuring in the working and balancing condyle when lower right canine, lower right first molar and lower right second molar were clenched by the three dimensional finite element analysis. Also, stress distribution in the working and balancing condyles were observed and compared when $20^{\circ}$ forward and buccal bite forces were applied to the first molar. The results were as follows : 1. Stress distribution in the condyles during unilateral clenching of the first molar, second molar, canine showed no difference. In the working condyle, tensile force was concentrated on the lateral aspect of the condylar articular surface and condylar neck. And compressive force was concentrated on the anteromedial and lateral aspect of condyle. In the balancing condyle, tensile and compressive forces were concentrated on the lateral aspect of the condylar articular surface and stress transmission to the temporal bone was not observed. 2. When lateral forces were applied to the first molar, tensile forces were concentrated on the medial aspect of the condylar neck and condylar posterior surface in working and balancing condyle. Compressive force was concentrated on the anteromedial and lateral surface of the condyle and stress transmission to the temporal bone was not observed. 3. During unilateral clenching, stress in the working condyle decreased as the occlusal load moved posteriorly while the stress in the balancing condyle increased. when lateral force was applied to first molar, the incremental amount of stress was greater than vertical load. 4. During unilateral clenching, the average balancing/working condyle stress ratio was 2.52. There was a greater concentration of stress in the balancing condyle. The ratio increased as the occlusal load moved posteriorly and decreased considerably when lateral forces were applied to the first molar.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.16 no.2
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• pp.161-171
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• 2006

The objectives of this study were to ergonomically evaluate varying tasks performed in a general hospital and to propose their improving measures based on the evaluation results. The tasks found in the hospital were largely classified into two groups of manual materials handling and awkward posture related tasks. Ergonomic tools of NLE, 3-D SSPP and RULA were used for evaluating workload of the tasks. The major findings are: 1) L5/S1 compressive force of patient transferring by one person exceeded the maximum permissible limit(6,400N) by NIOSH. The L5/S1 compressive forces for most of the patient transferring tasks by 2-4 persons were larger than the action limit (3,400N), and the tasks by five persons were analyzed to be safe in the view of L5/S1 compressive force; 2) patient repositioning tasks by 2-3 persons were hazardous on the basis of L5/S1 compressive force, while most of the tasks by 4-5 persons were safe; 3) many tasks performed in wards were found to be stressful, most of which resulted from improper heights of their working tables or working points. Of varying tasks in general hospitals, patient transferring was the most stressful. Based on the results of this study and high prevalence of musculoskeletal disorders from other studies, it is recommended that the ergonomics program be introduced and enforced for doing improving activities systematically

• Transactions of the Korean Society of Mechanical Engineers A
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• v.21 no.7
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• pp.1081-1088
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• 1997

The purpose of this work is to investigate the working limit of carbon steel and forging condition of cold forging. The fracture criteria which was proposed by Oyane and Osakada was used. Compression test, hardness study and tension test by Oyane's creteria, microstructure study by Osakada's were carried out. The results were compared with each other. It was found that working limit on compressive hydrostatic stress is increased in comparison with that of tensile stress field and can be forecasted the fracture limit of closed cold forging.

• Computers and Concrete
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• v.33 no.2
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• pp.137-145
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• 2024

The technique of experimentally determining concrete's compressive strength for a given mix design is time-consuming and difficult. The goal of the current work is to propose a best working predictive model based on different machine learning algorithms such as Gradient Boosting Machine (GBM), Stacked Ensemble (SE), Distributed Random Forest (DRF), Extremely Randomized Trees (XRT), Generalized Linear Model (GLM), and Deep Learning (DL) that can forecast the compressive strength of ternary geopolymer concrete mix without carrying out any experimental procedure. A geopolymer mix uses supplementary cementitious materials obtained as industrial by-products instead of cement. The input variables used for assessing the best machine learning algorithm not only include individual ingredient quantities, but molarity of the alkali activator and age of testing as well. Myriad statistical parameters used to measure the effectiveness of the models in forecasting the compressive strength of ternary geopolymer concrete mix, it has been found that GBM performs better than all other algorithms. A sensitivity analysis carried out towards the end of the study suggests that GBM model predicts results close to the experimental conditions with an accuracy between 95.6 % to 98.2 % for testing and training datasets.

• Journal of Korea Foundry Society
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• v.22 no.1
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• pp.17-25
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• 2002

Recently, many studies have been carried out to process on the purpose of lightness in a transport parts because of the saving energy, the environmental problem. The cast-forging process can be expected to lower costs without decreasing the mechanical properties. So, the finest microstructure is needed to get for applying the cast-forging process with Al-Si alloy because the microstructure affects to the cast-forging process. For refinement treatment of eutectic Si and Al solid-solution phase, Sr and TiB were added in Al-Si alloys. The finest microstructure could be observed when 0.075 wt.%Sr and 0.1 wt.%TiB were added respectively. In this case, tensile strength and elongation much more increased than as casting. After high temperature deformation simulation test with grain refinement specimens was carried out, about 70N per unit $area(mm^2)$ of specimen was confirmed. After hot forging, tensile strength and elongation were increased. It was considered because casting defect was removed by compressive working.

• Journal of Korea Foundry Society
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• v.22 no.1
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• pp.26-34
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• 2002

For application of cast-forging process with Al-Si alloys, casting experiments are carried out by adding Sr and TiB to Al-Si alloys for grain refinement treatment. We experimented on the mechanical properties according to microstructural changes, forging ability test and also investigated the mechanical properties after forging. The finest microstructure could be observed respectively when 0.05 wt.%Sr and 0.1 wt.%TiB were added. In this case, tensile strength and elongation increased much more than as casting. After high temperature deformation simulation test with grain refinement specimens was carried out, about 60N per unit $area(mm^2)$ of specimen was confirmed. After hot forging, tensile strength and elongation were increased. It was considered that casting defect was removed by compressive working.

• Computers and Concrete
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• v.32 no.3
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• pp.263-286
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• 2023

Experimenting with concrete to determine its compressive and tensile strengths is a laborious and time-consuming operation that requires a lot of attention to detail. Researchers from all around the world have spent the better part of the last several decades attempting to use machine learning algorithms to make accurate predictions about the technical qualities of various kinds of concrete. The research that is currently available on estimating the strength of concrete draws attention to the applicability and precision of the various machine learning techniques. This article provides a summary of the research that has previously been conducted on estimating the strength of concrete by making use of a variety of different machine learning methods. In this work, a classification of the existing body of research literature is presented, with the classification being based on the machine learning technique used by the researchers. The present review work will open the horizon for the researchers working on the machine learning based prediction of the compressive strength of concrete by providing the recommendations and benefits and drawbacks associated with each model as determining the compressive strength of concrete practically is a laborious and time-consuming task.

• International Journal of Automotive Technology
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• v.7 no.5
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• pp.579-584
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• 2006

Aluminum Resistance Spot Weld(Al RSW) is an enabling technology for body assembly of low mass fraction vehicles. Due to the unreliable durability of spot-welded joints, applications of Al RSW are limited. This study presents experimental investigation on the use of a post-weld cold working process to improve the fatigue strength of Al RSW. The post-weld cold working process includes special shaped indenters that are pressed or driven into the structure to induce compressive residual stresses. The mechanical properties of the post-weld cold worked Al RSW were investigated, including the experimental results of fatigue and micro-hardness tests. Comparisons of the mechanical properties and qualitative results between the as-welded RSW specimens and the post-weld cold worked RSW specimens are discussed. The post-weld cold worked Al RSW samples had an increase in both microhardness and fatigue life.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.3
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• pp.165-171
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• 2003

In a structure, many components are fastened together using bolts, nuts and rivets through drilled holes. Not only do these fastened joints enable easy assembly and dismantling, they are also able to transfer as well as to distribute loads applied onto the structures. The major drawback of such connections, however, is that the fatigue life of the components is reduced by the presence of the hole since the stress concentration around the hole is increased. In addition, the hole drilling process itself may introduce defects or roughness at the surfaces of the hole that may cause further decrease in fatigue performance of the components. For applications where fatigue loadings are important, one way to compensate the decrease in fatigue life of the components is by introduction of beneficial compressive residual stress around the hole using cold working. The material used for this research were A12024-T351 and A17050-T7451 using the primary member of aircraft. We present, In this paper, the characteristics of coldworking by evaluation of the hole expansion ratio, residual stress distribution, and fatigue properties.