Coursework — ME301, 10-phase structured study
Rocket Nozzle Throat Insert — Microstructure-Informed FEA
How big a manufacturing void can a rocket-nozzle throat insert tolerate at 1400°C before its factor of safety collapses to 1?
Inside the work
A high heat-flux region. A small margin.
Schematic converging-diverging nozzle section and throat-region thermal loading; colors do not encode computed temperatures or stresses.
Constrict
Hot gas approaches the throat, where the insert faces concentrated thermal loading.
Expand
Flow expands downstream while the material carries a nonuniform temperature field.
Assess
Thermo-structural analysis examines how defects change the insert’s response.
Overview
A 10-phase ME301 course study (proposal → material selection → geometry → mesh → loads → baseline solve → defect sensitivity sweep → NDT mapping → microstructure writeup → final report) of a solid rocket motor nozzle throat insert. The material is locked to C-103 (Nb-10Hf-1Ti), a BCC niobium alloy strengthened by solid-solution and precipitation hardening, chosen for retaining useful strength to roughly 1400°C — standard for rocket nozzle throats and re-entry leading edges.
The central engineering question is defect sensitivity: given that real castings and welds carry small voids, how does void size and depth-from-surface change the local stress-concentration factor and, ultimately, the factor of safety at operating temperature?
Dataset
10 configurations
5 defect radii × 2 depths (mid-wall, near-surface)
1400°C
Operating temperature evaluated for factor of safety
C-103 (Nb-10Hf-1Ti)
Locked material — full property set in materials/
Chart
Factor of safety vs. defect radius at 1400°C
Results
Defect sensitivity sweep — stress concentration factor and factor of safety at 1400°C
| Defect radius | Depth | Stress conc. Kₜ | FOS @ 1400°C |
|---|---|---|---|
| 0.2 mm | Mid-wall | 1.000 | 2.47 |
| 0.5 mm | Mid-wall | 0.997 | 2.48 |
| 1.0 mm | Mid-wall | 1.061 | 2.33 |
| 1.5 mm | Mid-wall | 1.127 | 2.19 |
| 2.0 mm | Mid-wall | 1.216 | 2.03 |
| 0.2 mm | Near-surface | 1.000 | 2.12 |
| 0.5 mm | Near-surface | 0.991 | 2.14 |
| 1.0 mm | Near-surface | 1.091 | 1.94 |
| 1.5 mm | Near-surface | 1.286 | 1.65 |
| 2.0 mm | Near-surface | 1.638 | 1.29 — critical |
Key Findings
What the work shows
The global stress field is dominated by the thermal gradient, not internal pressure — defect geometry only perturbs it locally.
Defect depth amplifies the stress-concentration factor non-linearly: the ratio of near-surface to mid-wall Kₜ grows from 1.00 at 0.2 mm radius to 1.35 at 2.0 mm.
A 2 mm near-surface void drives the factor of safety down to 1.29 at 1400°C — close enough to failure (FOS = 1) to be flagged as a critical defect class.
Practical implication carried into the NDT-mapping phase: near-surface voids larger than 1.5 mm within roughly a quarter wall-thickness of the bore must be reliably detectable by non-destructive testing before flight qualification.