A V-engine high pressure fuel pipe have experienced several failures during dyno engine validations at brazed joints due to combination of static and dynamic engine loads. The braze fillet experience high local stress concentration with large gradients and it was critical to capture strain contour at this spot to properly understand the failure. Strain gauges was used to measure strain but was incapable of capturing the braze fillet due to the small fillet radius and lack of real estate to install the gauge (braze fillet radius ~ 0.10 mm). A whole field optical experiment method Digital Image Correlation was utilized to successfully captured strain contour at area of interest and results fed back to computational model.
In this paper, experimental investigation and theoretical simulation have been carried out to measure and analyze the strain at braze fillets. 3D CAD modeling software Siemens NX was used to design and manufacture a light weight fixture which was used to install the high pressure fuel pipe in uniaxial tension compression machine and perform displacement control compression test. Digital Image Correlation (3D-DIC) is utilized successfully to measure the strain magnitude and contour distribution at braze fillet. In the simulation, Finite Element Analysis (FEA) model was developed for the fuel pipe and fixture assembly using 3D CAE software HyperMesh and Nastran, simulation was carried using same boundary conditions as DIC testing. The experimental and simulation results matched very well and validated the FEA model.
The detailed experimental and simulation procedures are demonstrated, and the results are also analyzed and correlated. Additional iterations were carried using the correlated FEA model to come up with new optimized design that reduced stress significantly and solved the braze failure problem.