Section 3 Load cases

3.1 General

3.1.1 To substitute the analytically determined SCF in the applicable Rules the following load cases have to be calculated.

3.2 Torsion

3.2.1 In analogy to the testing apparatus used for the investigations made by FVV (Forschungsvereinigung Verbrennungskraftmaschinen – Research Association for Combustion Engines), the structure is loaded in pure torsion. In the model, surface warp at the end faces is suppressed. Torque is applied to the central node located at the crankshaft axis. This node acts as the master node with 6 degrees of freedom and is connected rigidly to all nodes of the end face. Boundary and load conditions are valid for both in-line and V-type engines. See Figure 1.3.1 Boundary and load conditions for the torsional load case.

Figure 1.3.1 Boundary and load conditions for the torsional load case

3.2.2 For all nodes in both the journal and crank pin fillet, principal stresses are extracted and the equivalent torsional stress is calculated as follows:

3.2.3 The maximum value taken for the subsequent calculation of the SCF is:

Where:

τ_N is nominal torsional stress referred to the crankpin and respectively journal as per the applicable Rules with the torsional torque T:

3.3 Pure bending (4 point bending)

3.3.1 In analogy to the testing apparatus used for the investigations made by FVV the structure is loaded in pure bending. In the model, surface warp at the end faces is suppressed. The bending moment is applied to the central node located at the crankshaft axis. This node acts as the master node with 6 degrees of freedom and is connected rigidly to all nodes of the end face. Boundary and load conditions are valid for both in-line and V-type engines. See Figure 1.3.2 Boundary and load conditions for the pure bending load case.

3.3.2 For all nodes in both the journal and pin fillet, von Mises equivalent stresses σ_equiv are extracted. The maximum value is used to calculate the SCF according to:

where

Nominal stress σ_N is calculated as per the applicable Rules with the bending moment M:

σ_N

Figure 1.3.2 Boundary and load conditions for the pure bending load case

3.4 Bending with shear force (3-point bending)

3.4.1 This load case is calculated to determine the SCF for pure transverse force (radial force, β_ϱ) for the journal fillet. In analogy to the testing apparatus used for the investigations made by FVV, the structure is loaded in 3-point bending. In the model, surface warp at both end faces is suppressed. All nodes are connected rigidly to the centre node; boundary conditions are applied to the centre nodes. These nodes act as master nodes with 6 degrees of freedom. The force is applied to the centre node located at the pin centre-line of the connecting rod. This node is connected to all nodes of the pin cross sectional area. Warping of the sectional area is not suppressed.

3.4.2 Boundary and load conditions are valid for in-line and V-type engines. V-type engines can be modelled with one connecting rod force only. Using two connecting rod forces will make no significant change to the SCF. See Figure 1.3.3 Boundary and load conditions for the 3-point bending load case of an in-line engine and Figure 1.3.4 Load applications for in-line and V-type engines.

Figure 1.3.3 Boundary and load conditions for the 3-point bending load case of an in-line engine

Figure 1.3.4 Load applications for in-line and V-type engines

3.4.3 The maximum equivalent von Mises stress σ_3P in the journal fillet is evaluated. The SCF in the journal fillet can be determined in two ways as shown below.

Method 1: This method is analogous to the FVV investigation. The results from 3-point and 4-point bending are combined as follows:

where:

σ_3P as found by the FE calculation.

σ_N3P Nominal bending stress in the web centre due to the force F_3P [N] applied to the centreline of the actual connecting rod, see Figure 1.3.4 Load applications for in-line and V-type engines.

β_B as determined in Ch 1, 3.3 Pure bending (4 point bending).

σ_Q3P

where

Q_3P is the radial (shear) force in the web due to the force F_3P [N] applied to the centreline of the actual connecting rod, see also Figure Bending moment and shear force for in-line and V engine crankthrows in the applicable Rules.

Method 2: This method is not analogous to the FVV investigation. In a statically determined system with one crank throw supported by two bearings, the bending moment and radial (shear) force are proportional. Therefore the journal fillet SCF can be found directly by the 3-point bending FE calculation.
The SCF is then calculated according to:

For an explanation of the symbols see Ch 1, 3.4 Bending with shear force (3-point bending) 3.4.3.(a).

When using this method, the radial force and stress determination in the applicable Rules becomes superfluous. The alternating bending stress in the journal fillet as per the Calculation of bending stresses sub-Section of the applicable Rules is then evaluated:

Note that the use of this method does not apply to the crankpin fillet and that this SCF must not be used in connection with calculation methods other than those assuming a statically determined system as in the applicable Rules.