Analysis of crack initiation and propagation in solid rocket motor nozzle throats

Download

index.pdf

Date

2019

Author

Nigar, Barış

Metadata

Show full item record

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Item Usage Stats

373
views

300
downloads

Graphite is a widely used material in high temperature structural applications due to its high melting point and its mechanical strength and integrity at elevated temperatures. However, rocket nozzles made of graphite are subjected to very high temperatures and pressures that cause cracking and eventual failure. This thesis investigates the reasons of failure and explores design alternatives to overcome this problem. The experimental part of the thesis includes compression tests, tensile tests and fracture toughness tests on Mersen-2020 graphite. Compression and tensile tests showed a bimodular response. Fracture toughness tests involved Single Edge Notch Bend (SENB) specimens and demonstrated the brittle nature of graphite. Based on experimentally measured materials behavior of graphite, a two-dimensional finite element model investigated the crack propagation behavior. The analyses were done in three steps. The first step was the computational fluid dynamics analysis of the flow through the nozzle. Using the results of this step, second step predicted the temperature variations within the nozzle. The final and most extensive part of the modeling consisted of Extended Finite Element Method applied on the nozzle geometry experiencing thermal stresses based on the analysis in the second step. The results show that the cracks are mostly mode II cracks induced by the compressive stresses vi next to the flow surface of the nozzle. Within only 5 seconds, these cracks result in graphite pieces breaking off, which adversely affects the flow dynamics of the nozzle. The change in the flow directly impacts the desired thrust force and results in an unreliable performance. As the final part of the analysis, the thesis considered some alternative nozzle designs that utilize a segmented geometry consisting of individual graphite parts. Several geometries were analyzed for their crack propagation behavior. The results show that careful segmentation of the nozzle relieves the stresses in critical regions and delay the failure. The thesis provides insight into the mechanisms of failure in graphite rocket nozzles and presents a design approach for superior and more reliable performance.

Subject Keywords

Graphite., Graphite, Fracture, Crack propagation, Extended finite element analysis, Rocket nozzle.

URI

http://etd.lib.metu.edu.tr/upload/12624908/index.pdf
https://hdl.handle.net/11511/45172

Collections

Graduate School of Natural and Applied Sciences, Thesis

Suggestions

OpenMETU
Core

Investigating the mechanical properties of single walled carbon nanotube reinforced epoxy composite through finite element modelling Zuberi, Muhammad Jibran Shahzad; Esat, Volkan (2015-03-15) Varying experimental results on the mechanical properties of carbon nanotube reinforced polymer composites (CNTRPs) have been reported due to the complexities associated with the characterization of material properties in nano-scale. Insight into the issues associated with CNTRPs may be brought through computational techniques time- and cost-effectively. In this study, finite element models are generated in which single walled carbon nanotube models are embedded into the epoxy resin. For modelling interface...
ESTIMATING THE EFFECT OF CHIRALITY AND SIZE ON THE MECHANICAL PROPERTIES OF CARBON NANOTUBES THROUGH FINITE ELEMENT MODELLING Zuberi, Muhammad Jibran Shahzad; Esat, Volkan (2014-06-27) Carbon nanotubes (CNTs) are considered to be one of the contemporary materials exhibiting superior mechanical, thermal and electrical properties. A new generation state-of-the-art composite material, carbon nanotube reinforced polymer (CNTRP), utilizes carbon nanotubes as the reinforcing fibre element. CNTRPs are highly promising composite materials possessing the potential to be used in various areas such as automotive, aerospace, defence, and energy sectors.
Investigation of the Mechanical Properties of Al2O3 Reinforced Nickel Composite Coatings Yılmaz, Olgun; Karakaya, İshak (2018-03-15) Addition of inert ceramic particles improves the mechanical and tribological properties of nickel coatings significantly. Two different surfactants; ammonium lignosulfonate (ALS) and sodium dodecyl sulfate (SDS), were used in a typical sulfamate nickel plating solution in varying concentrations to arrange the floatation and wetting conditions of Al2O3 particles (~300 nm) in the electrolyte. In addition to the effect of surfactants, effects of current density and...
Investigation of the Mechanical Properties of Al2O3 Reinforced Nickel Composite Coatings Yılmaz, Olgun; Karakaya, İshak (2018-03-15) Addition of inert ceramic particles improves the mechanical and tribological properties of nickel coatings significantly. Two different surfactants; ammonium lignosulfonate (ALS) and sodium dodecyl sulfate (SDS), were used in a typical sulfamate nickel plating solution in varying concentrations to arrange the floatation and wetting conditions of Al2O3 particles (~300 nm) in the electrolyte. In addition to the effect of surfactants, effects of current density and...
Effect of expandable graphite on flame retardant, thermal and mechanical properties of thermoplastic polyurethane composites filled with huntite&hydromagnesite mineral Guler, Turkan; Tayfun, Umit; Bayramlı, Erdal; DOĞAN, Mehmet (2017-01-10) The effect of expandable graphite (EG) was studied on the flame retardant, thermal and mechanical properties of thermoplastic polyurethane (TPU) containing huntite&hydromagnesite (HH). According to the flammability tests results, the synergistic interaction was observed between HH and EG. The maximum limiting oxygen index (LOI value was observed at a ratio of 1:1 (HH:EG) and the highest vertical burning test (UL-94) rating of V0 was observed at a ratios of 4:1, 3:2 and 1:1. The synergistic interaction betwe...

Citation Formats

B. Nigar, “Analysis of crack initiation and propagation in solid rocket motor nozzle throats,” Thesis (M.S.) -- Graduate School of Natural and Applied Sciences. Mechanical Engineering., Middle East Technical University, 2019.