BJSFM is a well-established computational method for analyzing a hole in a composite laminate to generate membrane loading fields (Nx, Ny, Nxy) with or without bolt bearing loads.
The BJSFM program operates by computing the stress/strain field using Lekhnitskii’s classical solution of holes through laminated plates (Lekhnitskii, S.G. "Anisotropic Plates", Gordon and Breach Science Publishers, 1968). This approach considers the angle of the bolt loading, biaxial and shear loads, and the effect of biaxial far field bypass loading.
Composite failure is computed at evenly spaced angular increments around a hole using a selected ply-based failure theory such as: maximum strain, maximum stress, Tsai-Hill, Tsai-Wu, and Hoffman. The margin of safety used for laminate sizing optimization is the minimum margin occurring for any ply or angular point at the characteristic distance.
BJSFM computes the same stress/strain distribution as a finely meshed shell FEM, however this approach is much faster and more robust because it is not a function of mesh fineness. Bolt analyses are semi-empirical in that they all require experimental testing to establish the parameters that calibrate stress predictions. The issue becomes predicting failure load rather than predicting laminate stress/strain. To resolve the unknown relationship between failure and stress gradients, the practical approach is to determine a characteristic distance.
Analysis Input
The following parameters are required for the bolted joint stress field modeling analysis in HyperSizer:
- Fastener diameter
- Bearing force
- Load angle
- Joint correction factors
- Characteristic distance (D0t, D0c)
- Pristine lamina properties
- Bypass loads
- Finite fastener width (W)
Important: The BJSFM analysis uses the uncorrected orthotropic material properties to generate the stress field. HyperSizer uses uncorrected lamina allowables to compute the lamina strength margins of safety.
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