Dovetail Blade Attachments
Structural assessment of dovetail blade roots, including centrifugal seating, bearing and flank contact, bending, friction, edge loading, fillet stress, fretting and fatigue.
Dovetail load path
A dovetail root transfers blade centrifugal force through one or two principal inclined contact faces into the disc slot. The wedge geometry converts radial pull into normal contact force and can generate substantial transverse reaction. Aerodynamic bending and torsion then bias the load from one side to the other. The joint is simpler than a multi-lobe fir-tree but remains strongly dependent on contact geometry and friction.
Seating under rotation
Centrifugal load pulls the blade outward until the load-bearing flanks seat. Initial clearance, root position and contact stiffness determine where pressure develops. A fully tied interface cannot reproduce this seating and will generally give the wrong local stress. Nonlinear contact is appropriate when the attachment itself is being assessed, while a calibrated equivalent stiffness may be sufficient in a higher-level blade model.
Wedge action and contact force
The inclination of the dovetail flanks means the normal contact force can exceed the blade radial resultant. Friction modifies the relationship further. This is important for bearing pressure, disc-slot stress and fretting. Simple free-body resolution provides a useful estimate of expected normal force and is a good independent check on the FE contact solution.
Edge loading
Small angular mismatch or bending can concentrate pressure near one end of a flank. Manufacturing tolerance, disc deformation and thermal gradients can all contribute. Edge-loaded contact creates high local stress and can initiate surface damage. Accurate flank angle, chamfer and relief geometry may therefore matter more than very fine mesh elsewhere.
Fillet and neck stress
The blade neck above the dovetail and the disc slot fillets carry concentrated load paths and often govern fatigue. Use physical radii and appropriate mesh refinement. If a sharp idealisation creates a non-convergent stress, assess with a finite-radius model or a fatigue method designed for structural or notch stress. Compare blade-side and disc-side locations because either can govern.
Friction and slip
Friction can reduce bulk sliding while still allowing microslip near contact edges under vibration. The coefficient affects both normal/tangential load distribution and damping. Treat it as an uncertain interface property rather than a universal constant. Where HCF or fretting is critical, perform sensitivity and use surface-condition data or rig correlation if available.
Thermal and material effects
Blade and disc temperature differences change fit and contact. Material modulus and expansion coefficient alter stiffness and load sharing. Hot-section dovetails may operate at lower temperature than the aerofoil but can still experience strong gradients during transients. Use the local thermal field rather than applying aerofoil peak temperature to the whole root.
Fatigue and inspection
Repeated start-stop cycles change centrifugal contact and contribute to LCF, while vibration can drive HCF or fretting at the flanks. Inspection should target fillets, contact edges and known stress-concentration zones. If field damage appears away from the predicted hotspot, review contact and tolerance assumptions rather than simply increasing a stress factor.
Verification
Close the blade free body using integrated contact forces and moments. Check the predicted normal-force scale against a simple wedge free body. Review contact footprint, edge pressure, frictional traction and fillet convergence. Vary clearance and flank angle within drawing tolerance. A good model should show a stable, understandable seating mechanism.
Dovetail attachment stress is driven by contact geometry. A tied root may reproduce global blade stiffness while giving a misleading local fatigue picture.
Design sensitivity to flank geometry
Small changes in flank angle, contact length and relief geometry can shift bearing pressure and fillet stress substantially. Parametric analysis is therefore valuable during dovetail development. Rather than optimising only the minimum peak stress, examine how the joint responds to tolerance, friction and bending load. A geometry with slightly higher nominal stress but much lower sensitivity to manufacturing variation can be the stronger production design.
Engineering judgement — governing sensitivities
For Dovetail Blade Attachments, the most useful review question is not simply whether the solver has produced a plausible contour or scalar result, but whether the model preserves how blade pull, contact pressure, flank friction and attachment flexibility share load across the root geometry. Small changes in fit, thermal growth or contact state can shift peak pressure and local bending from one flank or fillet to another. This is where apparently small modelling choices can change the engineering conclusion. The analyst should identify the variables that can move the governing response, separate physical uncertainty from deliberate conservatism, and show that the selected modelling fidelity is proportionate to the decision being supported. Where the response is close to an acceptance boundary, sensitivity cases should bracket credible changes rather than apply arbitrary percentage perturbations.
Verification evidence for the engineering record
A defensible Dovetail Blade Attachments assessment should leave an evidence trail that another engineer can independently interrogate. At minimum, review contact-status maps, reaction balance, friction/preload sensitivity, root-fillet stress convergence, fit and tolerance effects, and comparison with simplified bearing/contact calculations or component test evidence. Numerical convergence should be demonstrated on the response quantity that drives the decision, not only on generic mesh or solver metrics. The report should distinguish verified numerical behaviour from validation against test or service evidence, record any extrapolation beyond the supporting data, and state which assumption would most likely change the conclusion. This turns the analysis from a plausible calculation into an auditable engineering substantiation.