ashfordeOU Composite Bolted Joints (structures/composites/composite-bolted-joints)
Use when the task is analyzing a bolted joint in a composite laminate: bearing and bypass loading, bolt bearing stress, net-tension, shear-out, and joint margins.
Domain quick reference
- A bolted joint transfers load through a fastener (bolt) of diameter D in a laminate of thickness t. The joint is sized against three local failure modes, each with its own allowable.
- Bearing stress: sigma_b = P_b / (D * t), where P_b is the load transferred through the bolt. The bearing allowable F_bru is the laminate or bolt bearing strength, whichever governs.
- Net-tension stress: sigma_nt = P / ((w - D) * t), where w is the joint width (or the tributary width per fastener, min(w, pitch) for a multi-fastener row). The net section w - D must be positive.
- Shear-out stress: sigma_so = P / (2 * e * t), where e is the edge distance from the hole center to the free edge in the load direction; two shear planes carry the load over length e.
- Bypass loading: with a bypass ratio r, the fraction of the total load carried around the hole through the laminate, P_bp = r * P and the bearing load P_b = (1 - r) * P. The net section still carries the full load P for a single fastener row.
- Joint margin: M = allowable / applied - 1. A margin of zero means the applied stress equals the allowable; negative margins fail.
- Joint efficiency: eta = (w - D) / w, the net-section to gross-section width ratio of the joint.
- Units are self-consistent (N, mm, MPa, or lbf, in, psi); stresses and allowables must share one unit system.
Workflow
- Collect the joint geometry and load: applied load P, bolt diameter D, laminate thickness t, joint width w, edge distance e, and pitch p when a fastener row is involved.
- Split the load with bypass_split(P, r) when a bypass ratio is specified; otherwise the full load is bearing load.
- Compute the three applied stresses: bearing_stress(P_b, D, t), net_tension_stress(P, w, D, t), shear_out_stress(P, e, t).
- Compute the margins with margin_of(allowable, applied) against the bearing, net-tension, and shear-out allowables.
- Use joint_analysis(...) for the one-shot report: stresses, margins, governing mode (lowest margin), pass or fail verdict, joint efficiency, and effective width.
Pitfalls
- A bolt diameter at or above the joint width destroys the net section: the logic raises ValueError.
- A bypass ratio outside [0, 1] is physically impossible: the logic raises ValueError.
- Reading the margin sign backwards: positive margins pass, a negative margin is a failure in that mode.
- Using the gross width instead of the net section (w - D) for the net-tension stress, or forgetting the two shear planes (factor 2) in the shear-out stress.
- Mixing unit systems: stresses and allowables must be in the same units for the margins to mean anything.
- Applying the single-fastener formulas to a complex multi-row joint without checking the tributary width per fastener (pitch).
Behavior contract (gate 3)
The bearing, bypass, net-tension, shear-out, and margin logic is exercised by the gate 3 contract test: scripts/test_composite_bolted_joints.py against scripts/composite_bolted_joints_logic.py (stdlib unittest, offline). Run:
python3 scripts/test_composite_bolted_joints.py
Compliance
- FAR-25 and CS-25 are referenced only as the certification context for structural joint substantiation; the formulas are standard mechanical joint analysis methodology (summary, no quoted text).
- compliance: STANDARDS-REF, gated: false.