Characterization of the Cohesive Strengths of Environmental Barrier Coatings to Ceramic Substrates Using Compression Tests

2002 ◽  
Author(s):  
Shanti V. Nair ◽  
Harry E. Eaton ◽  
Ellen Y. Sun ◽  
Greg C. Ojard
Keyword(s):  
Compression Test ◽  
Standard Test ◽  
Test Method ◽  
Compression Tests ◽  
Ceramic Substrates ◽  
Barrier Coatings ◽  
Test Fixture ◽  
Environmental Barrier Coatings ◽  
Environmental Barrier

The cohesive strengths of environmental barrier coatings applied to silicon carbide substrates were characterized using a compression test containing a strip of coating along a portion of the gage length. The substrate sample design and test fixture are similar to that described in ASTM D 695-96. The theory needed to extract the cohesive/adhesive strengths from the data is presented. The results of the compression tests are compared to the standard test method for the determination of the cohesive/adhesive strengths by the tension-adhesion test (TAT) (ASTM C 633-79). The preliminary results indicate that the onset of failure in the compression tests can be correlated with TAT test results, allowing for the extraction of the cohesive strength of the coating. For this system, this strength was found to be 15–20 MPa. The compression test has the advantage that it can be conducted at elevated temperature without the use of adhesives and, furthermore, is not limited by the adhesive strengths of polymeric adhesives.

Computational investigation of foreign object damage sustained by environmental barrier coatings (EBCs) and SiC/SiC ceramic-matrix composites (CMCs)

2015 ◽  
Vol 11 (2) ◽  
pp. 238-272 ◽  
Author(s):  
Mica Grujicic ◽  
Jennifer Snipes ◽  
Ramin Yavari ◽  
S. Ramaswami ◽  
Rohan Galgalikar
Keyword(s):  
Gas Turbine ◽  
Ceramic Matrix ◽  
Turbine Engines ◽  
Gas Turbine Engines ◽  
Foreign Object ◽  
Barrier Coatings ◽  
Content Type ◽  
Environmental Barrier Coatings ◽  
Foreign Object Damage ◽  
Environmental Barrier

Purpose – The purpose of this paper is to prevent their recession caused through chemical reaction with high-temperature water vapor, SiC-fiber/SiC-matrix ceramic-matrix composite (CMC) components used in gas-turbine engines are commonly protected with so-called environmental barrier coatings (EBCs). EBCs typically consist of three layers: a top thermal and mechanical protection coat; an intermediate layer which provides environmental protection; and a bond coat which assures good EBC/CMC adhesion. The materials used in different layers and their thicknesses are selected in such a way that the coating performance is optimized for the gas-turbine component in question. Design/methodology/approach – Gas-turbine engines, while in service, often tend to ingest various foreign objects of different sizes. Such objects, entrained within the gas flow, can be accelerated to velocities as high as 600 m/s and, on impact, cause substantial damage to the EBC and SiC/SiC CMC substrate, compromising the component integrity and service life. The problem of foreign object damage (FOD) is addressed in the present work computationally using a series of transient non-linear dynamics finite-element analyses. Before such analyses could be conducted, a major effort had to be invested toward developing, parameterizing and validating the constitutive models for all attendant materials. Findings – The computed FOD results are compared with their experimental counterparts in order to validate the numerical methodology employed. Originality/value – To the authors’ knowledge, the present work is the first reported study dealing with the computational analysis of the FOD sustained by CMCs protected with EBCs.

Determination of Steady-State Adhesive Wear Rate

2005 ◽  
Author(s):  
L. J. Yang
Keyword(s):  
Steady State ◽  
Wear Rate ◽  
Wear Test ◽  
Standard Test ◽  
Test Method ◽  
Testing Time ◽  
Wear Coefficient ◽  
Wear Rates ◽  
Test Methodology

Wear rates obtained from different investigators could vary significantly due to lack of a standard test method. A test methodology is therefore proposed in this paper to enable the steady-state wear rate to be determined more accurately, consistently, and efficiently. The wear test will be divided into four stages: (i) to conduct the transient wear test; (ii) to predict the steady-state wear coefficient with the required sliding distance based on the transient wear data by using Yang’s second wear coefficient equation; (iii) to conduct confirmation runs to obtain the measured steady-state wear coefficient value; and (iv) to convert the steady-state wear coefficient value into a steady-state wear rate. The proposed methodology is supported by wear data obtained previously on aluminium based matrix composite materials. It is capable of giving more accurate steady-state wear coefficient and wear rate values, as well as saving a lot of testing time and labour, by reducing the number of trial runs required to achieve the steady-state wear condition.

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