Target Size Effects on Foreign Object Damage in Gas-Turbine Grade Silicon Nitrides by Ceramic Ball Projectiles

2010 ◽  
Author(s):  
Sung R. Choi ◽  
Zsolt Ra´cz
Keyword(s):  
Silicon Nitride ◽  
Gas Turbine ◽  
Impact Velocity ◽  
Impact Damage ◽  
Target Thickness ◽  
Foreign Object ◽  
Silicon Nitrides ◽  
Foreign Object Damage ◽  
Post Impact ◽  
Grade Silicon

Foreign object damage (FOD) phenomena of two gas-turbine grade silicon nitrides (AS800 and SN282) were determined at ambient temperature using impact velocities ranging from 25 to 150 m/s by 1.59-mm diameter silicon nitride ball projectiles. Targets in flexure bar configuration with two different thicknesses of 1 and 2 mm were impacted under a fully supported condition. The degree of impact damage as well as of post-impact strength degradation increased with increasing impact velocity, increased with decreasing target thickness, and was greater in SN282 than in AS800 silicon nitride regardless of target thickness. The critical impact velocity, in which targets fractured catastrophically, decreased monotonically with decreasing target thickness and was lower in SN282 than in AS800. Backside cracking was dominant in both AS800 and SN282 target specimens with a thickness of 1 mm, occurring from an impact velocity of 50 m/s. A backside cracking analysis based on the elastic foundation approach was made as a function of target thickness. Overall, FOD by ceramic projectiles was significantly greater than that by hardened metallic counterparts.

Foreign Object Damage in Gas-Turbine Grade Silicon Nitrides by Silicon Nitride Ball Projectiles

2009 ◽  
Author(s):  
Sung R. Choi
Keyword(s):  
Silicon Nitride ◽  
Gas Turbine ◽  
Impact Velocity ◽  
Impact Damage ◽  
Hertzian Contact ◽  
Foreign Object ◽  
Silicon Nitrides ◽  
Foreign Object Damage ◽  
Critical Impact Velocity ◽  
Grade Silicon

Foreign object damage (FOD) behavior of two gas-turbine grade silicon nitrides (AS800 and SN282) was determined with a considerable sample size at ambient temperature using impact velocities ranging from 50 to 225 m/s by 1.59-mm diameter silicon nitride ball projectiles. The degree of impact damage as well as of post-impact strength degradation increased with increasing impact velocity, and was greater in SN282 than in AS800 silicon nitride. The critical impact velocity in which target specimens fractured catastrophically was remarkably low: about 200 and 130 m/s, respectively, for AS800 and SN282. The difference in the critical impact velocity and impact damage between the two target silicon nitrides was attributed to the fracture toughness of the target materials. The FOD by silicon nitride projectiles was significantly greater than that by steel ball projectiles. Prediction of impact force was made based on a yield model and compared with the conventional Hertzian contact-stress model.

Effects of Target Size on Foreign Object Damage in Gas-Turbine Grade Silicon Nitrides by Steel Ball Projectiles

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
Sung R. Choi ◽  
Zsolt Rácz
Keyword(s):  
Silicon Nitride ◽  
Gas Turbine ◽  
Impact Velocity ◽  
Steel Ball ◽  
Target Size ◽  
Hertzian Contact ◽  
Foreign Object ◽  
Silicon Nitrides ◽  
Foreign Object Damage ◽  
Grade Silicon

Foreign object damage (FOD) phenomena of two gas-turbine grade silicon nitrides (AS800 and SN282) were assessed at ambient temperature applying impact velocities from 20 to 300 m/s using 1.59-mm diameter hardened steel ball projectiles. Targets in a flexural configuration with two different sizes (thicknesses) of 1 and 2 mm were ballistic-impacted under a fully supported condition. The severity of impact damage, as well as the degree of post-impact strength degradation, increased with increasing impact velocity, increased with decreasing target size, and was greater in SN282 than in AS800 silicon nitride. The critical impact velocity where targets fractured catastrophically decreased with decreasing target size and was lower in SN282 than in AS800. Overall, FOD by steel projectiles was significantly less than that by silicon-nitride ceramic counterparts, due to much decreased Hertzian contact stresses. A correlation of backside cracking velocity versus target size was made based on a simplified elastic foundation analysis.

Effects of Target Size on Foreign Object Damage in Gas-Turbine Grade Silicon Nitrides by Steel Ball Projectiles

2011 ◽  
Author(s):  
Sung R. Choi ◽  
Zsolt Ra´cz
Keyword(s):  
Silicon Nitride ◽  
Gas Turbine ◽  
Impact Velocity ◽  
Steel Ball ◽  
Target Size ◽  
Hertzian Contact ◽  
Foreign Object ◽  
Silicon Nitrides ◽  
Foreign Object Damage ◽  
Grade Silicon

Foreign object damage (FOD) phenomena of two gas-turbine grade silicon nitrides (AS800 and SN282) were assessed at ambient temperature applying impact velocities from 20 to 300 m/s using 1.59-mm diameter hardened steel ball projectiles. Targets in a flexural configuration with two different sizes (thicknesses) of 1 and 2 mm were ballistic-impacted under a fully supported condition. The severity of impact damage, as well as the degree of post-impact strength degradation, increased with increasing impact velocity, increased with decreasing target size, and was greater in SN282 than in AS800 silicon nitride. The critical impact velocity where targets fractured catastrophically decreased with decreasing target size and was lower in SN282 than in AS800. Overall, FOD by steel projectiles was significantly less than that by silicon-nitride ceramic counterparts, due to much decreased Hertzian contact stresses. A correlation of backside cracking velocity versus target size was made based on a simplified elastic foundation analysis.

Foreign Object Damage of Two Gas-Turbine Grade Silicon Nitrides in a Thin Disk Configuration

2003 ◽  
Author(s):  
Sung R. Choi ◽  
J. Michael Pereira ◽  
Lesley A. Janosik ◽  
Ramakrishna T. Bhatt
Keyword(s):  
Impact Strength ◽  
Gas Turbine ◽  
Impact Velocity ◽  
Foreign Object ◽  
Silicon Nitrides ◽  
Foreign Object Damage ◽  
Post Impact ◽  
Grade Silicon ◽  
Thin Disks ◽  
The Impact

Foreign object damage (FOD) behavior of two commercial gas-turbine grade silicon nitrides, AS800 and SN282, was determined at ambient temperature through post-impact strength testing for thin disks impacted by steel-ball projectiles with a diameter of 1.59 mm in a velocity range from 115 to 440 m/s. AS800 silicon nitride exhibited a greater FOD resistance than SN282, primarily due to its greater value of fracture toughness (KIC). The critical impact velocity in which the corresponding post-impact strength yielded the lowest value was Vc ≈ 440 and 300 m/s for AS800 and SN282, respectively. A unique lower-strength regime was typified for both silicon nitrides depending on impact velocity, attributed to significant radial cracking. The damages generated by projectile impact were typically in the forms of ring, radial, and cone cracks with their severity and combination being dependent on impact velocity. Unlike thick (3 mm) flexure bar specimens used in the previous studies, thin (2 mm) disk target specimens exhibited a unique backside radial cracking occurring on the reverse side just beneath the impact sites at and above impact velocity of 160 and 220 m/s for SN282 and AS800, respectively.

Effect of Projectile Materials on Foreign Object Damage of a Gas-Turbine Grade Silicon Nitride

2005 ◽  
Author(s):  
Sung R. Choi ◽  
Zsolt Racz ◽  
Ramakrishna T. Bhatt ◽  
David N. Brewer ◽  
John P. Gyekenyesi
Keyword(s):  
Silicon Nitride ◽  
Impact Velocity ◽  
Impact Load ◽  
Impact Damage ◽  
Hardened Steel ◽  
Foreign Object ◽  
Foreign Object Damage ◽  
Post Impact ◽  
Critical Impact Velocity ◽  
Steel Balls

Foreign object damage (FOD) behavior of AS800 silicon nitride was determined using four different projectile materials at ambient temperature. The target test specimens rigidly supported were impacted at their centers by spherical projectiles with a diameter of 1.59 mm. Four different types of projectiles were used including hardened steel balls, annealed steel balls, silicon nitride balls, and brass balls. Post-impact strength of each target specimen impacted was determined as a function of impact velocity to better understand the severity of local impact damage. The critical impact velocity where target specimens fail upon impact was highest with brass balls, lowest with ceramic ball, and intermediate with annealed and hardened steel balls. Degree of strength degradation upon impact followed the same order as in the critical impact velocity with respect to projectile materials. For steel balls, hardened projectiles yielded more significant impact damage than annealed counterparts. The most important material parameter affecting FOD was identified as hardness of projectiles and was correlated in terms of critical impact velocity, impact deformation, and impact load.

Foreign object damage in flexure bars of two gas-turbine grade silicon nitrides

2004 ◽  
Vol 379 (1-2) ◽  
pp. 411-419 ◽  
Author(s):  
Sung R. Choi ◽  
J.Michael Pereira ◽  
Lesley A. Janosik ◽  
Ramakrishna T. Bhatt
Keyword(s):  
Gas Turbine ◽  
Foreign Object ◽  
Silicon Nitrides ◽  
Foreign Object Damage ◽  
Grade Silicon

Foreign Object Damage in an Oxide/Oxide Composite at Ambient Temperature

2008 ◽  
Vol 131 (2) ◽  
Author(s):  
Sung R. Choi ◽  
Donald J. Alexander ◽  
Robert W. Kowalik
Keyword(s):  
Impact Strength ◽  
Ambient Temperature ◽  
Impact Damage ◽  
Ceramic Matrix Composite ◽  
High Energy ◽  
Strength Degradation ◽  
Foreign Object ◽  
Foreign Object Damage ◽  
Oxide Composite ◽  
Post Impact

Foreign object damage behavior of an oxide/oxide (N720/AS) ceramic matrix composite was determined at ambient temperature using impact velocities ranging from 100 m/s to 400 m/s by 1.59 mm diameter steel-ball projectiles. Two different support configurations of target specimens were used: fully supported and partially supported. The degree of post-impact strength degradation increased with increasing impact velocity and was greater in a partially supported configuration than in a fully supported one. For the fully supported configuration, frontal contact stress played a major role in generating composite damage, while for the partially supported case, both frontal contact and backside flexure stresses were the combined sources of damage generation. The oxide/oxide composite was able to survive high energy (∼1.3 J) impacts without complete structural failure. The degree of relative post-impact strength degradation of the oxide/oxide composite was similar to that of an advanced SiC/SiC composite observed from a previous study, regardless of the type of specimen support. Like the SiC/SiC composite, impact-damage tolerance was greater in the oxide/oxide than in monolithic silicon nitride ceramics for impact velocities >300 m/s.

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