Modelling the fracture behaviour of thermal barrier coatings containing healing particles

The performance of a self-healing Thermal Barrier Coating (TBC) containing dispersed healing particles depends crucially on the mismatch in thermomechanical properties between the healing particles and the TBC matrix. The present work systematically investigates this phenomenon based on numerical simulations using cohesive element-based finite element analysis. The effect of the mismatch in Coefficient of Thermal Expansion (CTE) and fracture strength between the healing particles and the matrix on the fracture characteristics is quantified in detail. Unit cell-based analyses are conducted on a representative self-healing TBC system under a thermal loading step typically experienced by TBC systems in jet turbines. Two different simulation setups are considered within the TBC unit cell namely (i) a single pair of healing particles and (ii) a randomly distributed array of healing particles. The results of the simulations are reported in terms of the fracture pattern, crack initiation temperature and crack length for various CTE mismatch ratios. Correlations are established between the results obtained from the two simulation setups essentially revealing the effect of spatial distribution and proximity of healing particles on the fracture pattern. The results obtained from the analyses can be utilised to achieve a robust design of a self-healing TBC system

Thermal cyclic behavior and lifetime prediction of self-healing thermal barrier coatings

The thermal cyclic behavior of self-healing thermal barrier coatings (SH-TBC) is analyzed numerically to develop a lifetime prediction model. Representative microstructures are studied adopting a unit cell based multiscale modeling approach along with a simplified evolution model for the thermally-grown oxide layer (TGO) to study the evolution of damage and healing in a self-healing TBC system. The fracture and healing process is modeled using the cohesive zone-based healing model along with a crack tracking algorithm. The microstructural model includes splat boundaries and a wavy interface between the Top Coat and the Bond Coat, typical of Air Plasma Sprayed TBCs. A particle-based self-healing mechanism is accounted for with a random distribution of healing particles subjected to a numerically accelerated thermal cyclic loading condition. Lifetime extension of the self healing TBCs is quantified by conducting thermal cyclic analyses on conventional TBCs (benchmark system without self-healing particles). Parametric analyses on healing parameters such as crack filling ratio and strength recovery of the healed crack are also conducted. The results are presented in terms of the evolution of the crack pattern and the number of cycles to failure. For self-healing TBCs with a suitable healing reaction (i.e., cracks being partially filled and a minimal local strength after healing), an improvement in TBC lifetime is observed. In contrast, if the healing mechanism is not activated, the presence of the healing particles is actually detrimental to the lifetime of the TBC. Correspondingly, in addition to superior crack filling ratio and healed strength, significant improvement in lifetime is achieved for self healing TBCs with a higher probability of crack-healing particle interaction. This highlights the importance of a robust activation mechanism and a set of key material requirements in order to achieve successful self-healing of the TBC system

Influence of embedded MoSi2 particles on the high temperature thermal conductivity of SPS produced yttria-stabilised zirconia model thermal barrier coatings

To prolong the lifetime of thermal barrier coatings (TBCs) recently a new method of microcrack healing has been developed, which relies on damage initiated thermal decomposition of embedded molybdenum disilicide (MoSi2) particles within the TBC matrix. While these MoSi2 particles have a beneficial effect on the structural stability of the TBC, the high thermal conductivity of MoSi2 may have an unfavourable but as yet unquantified impact on the thermal conductivity of the TBCs. In this work the thermal conductivity of spark plasma sintering (SPS) produced yttria-stabilised zirconia (YSZ) model thermal barrier coatings containing 10 or 20 vol.% of MoSi2 healing particles was investigated using the laser flash method. Measurements were performed on free-standing composite material over a temperature range from room temperature up to 1000 °C. Microstructural analysis was carried out by SEM combined with image analysis to determine the size, distribution and area fraction of healing particles. The measurements were compared with the results from microstructure-based multi-physics finite element (FE) models and analytical models (the asymmetric Bruggeman model and the Nielsen model) in order to study the effects of the addition of MoSi2 particles as well as the presence of micro-pores on the apparent thermal conductivity. The results show a strongly non-linear increase in the thermal conductivity of the composite material with the MoSi2 volume fraction and a dependence on the aspect ratio of MoSi2 particles. Interparticle connectivity is shown to play a big role too

The use of films on history education in primary schools: Problems and suggestions

The use of films has a very important place among the alternative teaching tools, which can be used for achieving effective learning by helping to gather students' interest for the learning material. For the effective use of films on history education as an additional tool and avoiding possible harmful effects on students by the misuse, primarily the teachers should be educated for efficiency on the use of films as an educational tool. In this frame, teachers should be able to both reinforce learning and enhance critical thinking skills of their students by additional learning activities carried out before and after the film use

In Vitro Comparative Analysis of Fracture Resistance in Inlay Restoration Prepared with CAD-CAM and Different Systems in the Primary Teeth

Objective. The aim of this study was to compare to fracture resistance test of inlay restorations prepared using direct inlay technique (Gradia® Direct Composite) and Indirect Restoration System® (Gradia Indirect Composite) and CAD/CAD system (Vita Enamic® Block). Study Design. 48 noncarious extracted maxillary second primary molars were randomly divided into 4 groups with 12 in each group. All the teeth were prepared based on inlay class II preparations except for the control group. Other groups were restored with Gradia Direct Composite, Gradia Indirect Composite, and Vita Enamic Block, respectively. All restorations were cemented self-adhesive dual cure resin (3M Espe, RelyX™ Unicem Aplicap). A fracture test was performed using a compressive load. Results were analyzed using one-way analysis of variance and Duncan’s post hoc multiple comparison tests (α=0.05). Results. Vita Enamic Block and Gradia Indirect Composite showed significantly higher fracture resistance than Gradia Direct Composite (p<0.05). There was no significant difference fracture resistance between Vita Enamic Block and Gradia Indirect Composite (p>0.05). All restorations tested led to a significant reduction in fracture resistance (p<0.05). Conclusion. In inlay restorations, Indirect Restoration Systems and CAD/CAM systems were applied successfully together with the self-adhesive dual cure resin cements in primary molars

Fracture resistance force of primary molar crowns milled from Polymeric computer‑aided design/computer‑assisted manufactured resin blocks

Purpose: To compare fracture resistance force (FRF) and failure types of crowns milled from resin nanoceramic (Lava Ultimate)‑, and modified polymethylmethacrylate (PMMA) (Vita computer‑aided design (CAD)‑Temp)‑, and PMMA (Telio CAD)‑based  CAD/computer‑assisted manufactured (CAM) blocks.Materials and Methods: Three experimental groups of 10 milled crowns were arranged: Group‑1 (Lava Ultimate), Group‑2 (Vita CAD‑Temp), and Group‑3 (Telio CAD). Crowns were machined in sizes similar to a primary second molar stainless steel crown (SSC) and stored in water at 37°C for 30 days. The crowns were seated on Cr‑Co dies. Their FRFs were measured using a universal test machine until fracture. FRFs and failure types were recorded and statistically analyzed (P &lt; 0.05). Results: There were statistically significant differences among the groups for both FRFs and failure types. The sources of significant differences for FRFs and failure types were Group‑3 and Group‑1, respectively.Conclusion: Crowns milled from different chemical structural CAD/CAM blocks may be used for restoration of primary molar teeth.Keywords: Computer‑aided design/computer‑assisted manufactured resin, fracture resistance force, primary molar crown

Dental Treatments under the General Anesthesia in a Child with Keratitis, Ichthyosis, and Deafness Syndrome

KID syndrome is a rare genodermatosis characterized by keratitis, ichthyosis, and sensorineural deafness. Although the dermatological, ophthalmologic, and sensorineural defects are emphasized in the literature, oral and dental evaluations are so superficial. In this case report, dental and oral symptoms of a three year and five months old boy with KID syndrome, suffering severe Early Childhood Caries (s-ECC) and dental treatments done under General Anesthesia (GA) were reported

Pre-service science teacher practice of mathematics in operational physics and chemistry problems

The aims of this research are: to define Mathematics usage inclinations of pre-service science teachers in operational physics and chemistry problems and to evaluate them in terms of various socio-demographic varieties. The development study of Mathematics usage scale in Operational Physics and Chemistry Problems (MUSOPCP) constitutes the first stage of the research. For the second stage of the research, the scale which is developed by the researchers has been applied to 173 pre-services science teacher. SPSS 16.00 is used to analyze the data. The results give us the conclusion that the pre-services are conscious of Conceptual knowledge and Mathematics Knowledge Relation in Operational Physics and Chemistry but they have higher Mathematics anxiety than expected while solving operational Physics and Chemistry problems. (C) 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Prof. Huseyin Uzunboylu

The reflection of critical thinking dispositions on operational chemistry and physics problems solving of engineering faculty students

The aim of this research is to investigate the reflections on operational chemistry and physics problems solving critical thinking dispositions of engineering faculty students. This research is designed as relational scanning model. The sample of this study, Chemistry, Chemical Engineering, Electrical-Electronics Engineering last year students taking "General Chemistry" and "General Physics" course has formed. In the study; The California Critical Thinking Disposition Inventory (CCTDI-R), which is improved by Facione, Facione and Giancarlo (1998) and adapted to Turkish by Kokdemir (2003). and "Mathematics usage scale in Operational Chemistry and Physics Problems" (MUSOPCP) with two factors which is developed by Ozsoy-Gunes, Derelioglu, Kirbaslar (2011) are used as tool of data collection. In order to analyze the data, SPSS 16.00, ANOVA, independent T-Test, Pearson correlation coefficient techniques are used. As a result, between CCTDI-R scale with mathematics anxiety in chemistry and physics problems factor of MUSOPCP has a negative relation and with mathematics knowledge factor of MUSOPCP has a positive relation. The significant differences were found between the departments with mathematics anxiety factor score of MUSOPCP and between the gender with mathematics knowledge factor score of MUSOPCP. The significant differences weren't found between gender and department with CCTDI-R scale; but according to graduated secondary school, significant differences were found between with CCTDI-R scale. (C) 2015 The Authors. Published by Elsevier Ltd