First load takes ~15 seconds; cached on subsequent loads.
Material Database
Interaction Law
When to use each curve
Linear (n=1): conservative baseline. No test data, or first-pass sizing with low bypass ratios.
Quadratic (n=2): typical for CFRP — supported by most coupon test databases. Best default for fastened CFRP lap-joints with balanced laminates.
Cubic (n=3): less conservative near the knee. Use only with substantiated coupon data for the specific material and lay-up.
Applied Loads
Bearing Peaking Factor
FEA Forces - Tension
FEA Forces - Compression
Allowables (B-Basis, ksi) - per environment
Results - all environments
How to read the chart.
The plot shows the bearing-bypass interaction envelope for each environment: above each curve is failing, below is passing.
The X-axis is bypass stress with compression on the left and tension on the right; the Y-axis is bearing stress.
Tension allowable is OHT (Open Hole Tension); compression allowable is BIID (Barely Visible Impact Damage compression - the damaged-state allowable).
The black circle marks the applied tension state; the black diamond marks the applied compression state.
MS ≥ 0 passes; MS < 0 fails (red); 0 ≤ MS < 0.15 is amber (low margin).
Calculation sheetMaterial databaseTheory and limitations
Interaction equation: peak failure of a bolted composite joint under combined bearing and net-section bypass loading is approximated by the power-law envelope
(σbr / Fbr)n + (σbp / Fbp)n = 1
with the exponent n selected per program convention. For each environment the bypass allowable Fbp = OHT in tension and Fbp = BIID in compression (BIID is the damaged-state compressive allowable - much more conservative than UNC or OHC).
Reserve factor: RF = (1/I)1/n where I is the interaction index. Margin of safety MS = RF - 1.
Bypass area for tubes: Abypass = πDt - the bypass load is shared around the entire annular cross-section.
For flat laminates: Abypass = w·t (net section width times thickness).
Bearing area: Abearing = d·t (single bolt diameter times laminate thickness). A peaking factor Kp accounts for non-uniform contact stress from bolt-hole clearance.
Limitations: the envelope is an empirical curve fit to coupon test data, not a first-principles strength model. For highly off-axis lay-ups or thick laminates, finite-element analysis with progressive damage may be required. BIID values assume standard impact energy per CMH-17; programs with custom impact threats should re-test. Single-shear vs double-shear bearing allowables differ - select the column matching your joint configuration.