Dog bone shaped specimen testing method to evaluate tensile strength of rock materials

Komurlu, Eren,Kesimal, Ayhan,Demir, Aysegul Durmus Techno-Press 2017 Geomechanics & engineering Vol.12 No.6

To eliminate the holding and gluing problems making the direct tensile strength test hard to be applied, a new method of testing specimens prepared using lathe machine to make the dog bone shape is assessed whether it could be applied to determine accurate direct tensile strength values of rock materials. A series of numerical modelling analyses was performed using finite element method to investigate the effect of different specimen and steel holder geometries. In addition to numerical modelling study, a series of direct tensile strength tests was performed on three different groups of rock materials and a rock-like cemented material to compare the results with those obtained from the finite element analyses. A proper physical property of the lathed specimens was suggested and ideal failure of the dog bone shaped specimens was determined according to the results obtained from this study.

In situ horizontal stress effect on plastic zone around circular underground openings excavated in elastic zones

Komurlu, Eren,Kesimal, Ayhan,Hasanpour, Rohala Techno-Press 2015 Geomechanics & engineering Vol.8 No.6

In this study, effect of horizontal in situ stress on failure mechanism around underground openings excavated in isotropic, elastic rock zones is investigated. For estimating the plastic zone occurrence, an induced stress influence area approach (Bray Equations) was modified to define critical stress ratio according to the Mohr-Coulomb failure criterion. Results obtained from modified calculations were compared with results of some other analytical solutions for plastic zone thickness estimation and the numerical modelling (finite difference method software, FLAC2D) study. Plastic zone and its geometry around tunnels were analyzed for different in situ stress conditions. The modified equations gave similar results with those obtained from the other approaches. However, safer results were calculated using the modified equations for high in situ stress conditions and excessive ratio of horizontal to vertical in situ stresses. As the outcome of this study, the modified equations are suggested to use for estimating the plastic zone occurrence and its thickness around the tunnels with circular cross-section.

Experimental and numerical analyses on determination of indirect (splitting) tensile strength of cemented paste backfill materials under different loading apparatus

Komurlu, Eren,Kesimal, Ayhan,Demir, Serhat Techno-Press 2016 Geomechanics & engineering Vol.10 No.6

The indirect tensile strengths (ITSs) of different cemented paste backfill mixes with different curing times were determined by considering crack initiation and fracture toughness concepts under different loading conditions of steel loading arcs with various contact angles, flat platens and the standard Brazilian test jaw. Because contact area of the ITS test discs developes rapidly and varies in accordance with the deformability, ITSs of curing materials were not found convenient to determine under the loading apparatus with indefinite contact angle. ITS values increasing with an increase in contact angle can be measured to be excessively high because of the high contact angles resulted from the deformable characteristics of the soft paste backfill materials. As a result of the change of deformation characteristics with the change of curing time, discs have different contact conditions causing an important disadvantage to reflect the strength change due to the curing reactions. In addition to the experimental study, finite element analyses were performed on several types of disc models under various loading conditions. As a result, a comparison between all loading conditions was made to determine the best ITSs of the cemented paste backfill materials. Both experimental and numerical analyses concluded that loading arcs with definite contact angles gives better results than those obtained with the other loading apparatus without a definite contact angle. Loading arcs with the contact angle of $15^{\circ}$ was found the most convenient loading apparatus for the typical cemented paste backfill materials, although it should be used carefully considering the failure cracks for a valid test.

Sulfide-rich mine tailings usage for short-term support purposes: An experimental study on paste backfill barricades

Komurlu, Eren,Kesimal, Ayhan Techno-Press 2015 Geomechanics & engineering Vol.9 No.2

Barricade failures generally occur at the early times of paste backfill when it is fresh in the stopes. The backfill strength increases and need for barricading pressure decreases as a result of the hydration reactions. In this study, paste backfill barricades of Cayeli copper mine were investigated to design cemented mineral processing plant tailings as barricade body concrete. Paste backfill in sub-level caving stopes of the mine needs to be barricaded for only four or five days. Therefore, short term strength and workability tests were applied on several cemented tailings material designs. Barricade failure mechanisms, important points of barricade designing and details of the new concrete material are explained in this work. According to the results obtained with this experimental study, the tailings were assessed to be used in concrete applied as temporary supports such as cemented paste backfill barricades.

Effects of metal surface grinding at the porcelain try-in stage of fixed dental prostheses

Kilinc, Halil Ibrahim,Kesim, Bulent,Gumus, Hasan Onder,Dincel, Mehmet,Erkaya, Selcuk The Korean Academy of Prosthodonitics 2014 The Journal of Advanced Prosthodontics Vol.6 No.4

PURPOSE. This study was to evaluate the effect of grinding of the inner metal surface during the porcelain try-in stage on metal-porcelain bonding considering the maximum temperature and the vibration of samples. MATERIALS AND METHODS. Ninety-one square prism-shaped ($1{\times}1{\times}1.5mm$) nickel-chrome cast frameworks 0.3 mm thick were prepared. Porcelain was applied on two opposite outer axial surfaces of the frameworks. The grinding was performed from the opposite axial sides of the inner metal surfaces with a low-speed handpiece with two types of burs (diamond, tungsten-carbide) under three grinding forces (3.5 N, 7 N, 14 N) and at two durations (5 seconds, 10 seconds). The shear bond strength (SBS) test was performed with universal testing machine. Statistical analyzes were performed at 5% significance level. RESULTS. The samples subjected to grinding under 3.5 N showed higher SBS values than those exposed to grinding under 7 N and 14 N (P<.05). SBS values of none of the groups differed from those of the control group (P>.05). The types of bur (P=.965) and the duration (P=.679) did not affect the SBS values. On the other hand, type of bur, force applied, and duration of the grinding affected the maximum temperatures of the samples, whereas the maximum vibration was affected only by the type of bur (P<.05). CONCLUSION. Grinding the inner metal surface did not affect the metal-porcelain bond strength. Although the grinding affected the maximum temperature and the vibration values of the samples, these did not influence the bonding strength.

Effects of metal surface grinding at the porcelain try-in stage of fixed dental prostheses

Halil İbrahim Kılınç,Bülent Kesim,Hasan Önder Gümüş,Mehmet Dinçel,Selçuk Erkaya 대한치과보철학회 2014 The Journal of Advanced Prosthodontics Vol.6 No.4

PURPOSE. This study was to evaluate the effect of grinding of the inner metal surface during the porcelain try-in stage on metal-porcelain bonding considering the maximum temperature and the vibration of samples. MATERIALS AND METHODS. Ninety-one square prism-shaped (1 × 1 × 1.5 mm) nickel-chrome cast frameworks 0.3 mm thick were prepared. Porcelain was applied on two opposite outer axial surfaces of the frameworks. The grinding was performed from the opposite axial sides of the inner metal surfaces with a low-speed handpiece with two types of burs (diamond, tungsten-carbide) under three grinding forces (3.5 N, 7 N, 14 N) and at two durations (5 seconds, 10 seconds). The shear bond strength (SBS) test was performed with universal testing machine. Statistical analyzes were performed at 5% significance level. RESULTS. The samples subjected to grinding under 3.5 N showed higher SBS values than those exposed to grinding under 7 N and 14 N (P<.05). SBS values of none of the groups differed from those of the control group (P>.05). The types of bur (P=.965) and the duration (P=.679) did not affect the SBS values. On the other hand, type of bur, force applied, and duration of the grinding affected the maximum temperatures of the samples, whereas the maximum vibration was affected only by the type of bur (P<.05). CONCLUSION. Grinding the inner metal surface did not affect the metalporcelain bond strength. Although the grinding affected the maximum temperature and the vibration values of the samples, these did not influence the bonding strength.

Carcinoma of the Tongue: A Case-control Study on Etiologic Factors and Dental Trauma

Bektas-Kayhan, Kivanc,Karagoz, Gizem,Kesimli, Mustafa Caner,Karadeniz, Ahmet Nafiz,Meral, Rasim,Altun, Musa,Unur, Meral Asian Pacific Journal of Cancer Prevention 2014 Asian Pacific journal of cancer prevention Vol.15 No.5

Background: Carcinoma of the tongue is the most common intra-oral malignancy in Western countries. Incidence and mortality rates have increased in recent years, and survival has not improved. This study aimed to determine etiologic factors for tongue cancer with age-sex matched case-control data. Materials and Methods: 47 patients with carcinoma of the tongue referred to our oral medicine clinic between years 2005-2006 were analyzed and compared with control group data. The medical records, including family history of cancer, dental trauma, and history of abuse of alcohol and tobacco products was recorded for all subjects. Chi square comparison tests and linear regression analysis were performed using the SPSS program for statistics. Results: Patient and randomly selected control groups each consisted of 30 male and 17 female subjects with mean ages 53.2 (${\pm}12.6$) and 52.6 (${\pm}11.5$) years respectively. Smoking and alcohol abuse proportions were significantly higher in the patient group (p=0.0001, p<0.0001 respectively). Chronic mechanical trauma was observed in 44.7% of the patients and 17.0% of the control group (p=0.004). Similarly, family history of cancer of any type (for the first degree relatives) was found to be more common in the patient group (p=0.009). On regression analysis, alcohol abuse, family history of cancer, smoking, chronic mechanical traumas appeared as significant etiologic factors (p=0.0001). Conclusions: We believe that field cancerization may become evident in oral and oropharyngeal mucosa with multiple steps of molecular changes starting from the first sign of dysplasia with chronic exposure to etiological factors. Chronic trauma cases need particular attention to search for very early signs of cancer.

Alveolar Bone Protective and Hypoglycemic Effects of Systemic Propolis Treatment in Experimental Periodontitis and Diabetes Mellitus

Cu¨neyt Asım Aral,Servet Kesim,Henry Greenwell,Mehmet Kara,Aysun Cxetin,Birkan Yakan 한국식품영양과학회 2015 Journal of medicinal food Vol.18 No.2

The aim of this study was to evaluate the efficacy of the anti-inflammatory effects of propolis on the systemic and local effects on experimental periodontitis and diabetes. Fifty-six Wistar rats were divided into seven groups: (1) negativecontrol (NC), (2) periodontitis (P), (3) diabetes (D), (4) diabetes + periodontitis (DP), (5) periodontitis + propolis (P-Pro), (6) diabetes + propolis (D-Pro), and (7) diabetes + periodontitis + propolis (DP-Pro). Periodontitis was induced by ligature placement and diabetes was induced by streptozotocin injection. Propolis (Pro) was administrated by oral gavage (100 mg/kg/day). On day 21, plasma was obtained for analysis and alveolar bone level was evaluated using histomorphometric analysis. Compared to NC the final blood glucose levels for D-Pro was not significantly different (P = .052), however, D, DP, and DPPro were significantly different. There were no statistically significant differences in blood glucose concentrations between P and P-Pro, between D and D-Pro, and between DP and DP-Pro. All groups showed significantly more alveolar bone loss compared with NC. A significant difference in bone loss was found between P and P-Pro, and DP and DP-Pro, however there was no difference between D and D-Pro. Plasma interleukin 1beta (IL-1β), tumor necrosis factor-alpha (TNF-α), and matrix metalloproteinase-8 (MMP-8) levels were not significantly different among groups. In conclusion, propolis reduced fasting blood glucose levels in diabetes. In addition, propolis might be beneficial as an adjunct treatment of diabetes associated periodontitis and periodontitis without diabetes.

Effects of metal surface grinding at the porcelain try-in stage of fixed dental prostheses

Mehmet Dincel,Hasan Onder Gumus,Selcuk Erkaya,Bulent Kesim,Halil İbrahim Kılınc 대한치과보철학회 2014 The Journal of Advanced Prosthodontics Vol.6 No.4

PURPOSE This study was to evaluate the effect of grinding of the inner metal surface during the porcelain try-in stage on metal-porcelain bonding considering the maximum temperature and the vibration of samples. MATERIALS AND METHODS Ninety-one square prism-shaped (1 × 1 × 1.5 mm) nickel-chrome cast frameworks 0.3 mm thick were prepared. Porcelain was applied on two opposite outer axial surfaces of the frameworks. The grinding was performed from the opposite axial sides of the inner metal surfaces with a low-speed handpiece with two types of burs (diamond, tungsten-carbide) under three grinding forces (3.5 N, 7 N, 14 N) and at two durations (5 seconds, 10 seconds). The shear bond strength (SBS) test was performed with universal testing machine. Statistical analyzes were performed at 5% significance level. RESULTS The samples subjected to grinding under 3.5 N showed higher SBS values than those exposed to grinding under 7 N and 14 N (P<.05). SBS values of none of the groups differed from those of the control group (P>.05). The types of bur (P=.965) and the duration (P=.679) did not affect the SBS values. On the other hand, type of bur, force applied, and duration of the grinding affected the maximum temperatures of the samples, whereas the maximum vibration was affected only by the type of bur (P<.05). CONCLUSION Grinding the inner metal surface did not affect the metal-porcelain bond strength. Although the grinding affected the maximum temperature and the vibration values of the samples, these did not influence the bonding strength.