INTERNATIONAL COUNCIL
ON COMBUSTION ENGINESCONSEIL INTERNATIONAL
DES MACHINES A COMBUSTION

CO-ORDINATING WORKING GROUP"CLASSIFICATION SOCIETIES – DIESEL"(WG2)

Proposal by CIMAC WG4
11th May 2012

IACS UR M53, Appendix VI“Guidance for calculation ofStress Concentration Factors
in the oil bore outlets of crankshafts throughutilisation of the Finite Element Method”

-2-Contents
1.
2.

General................................................................................................................ 3
Model requirements ............................................................................................. 3
2.1. Element mesh recommendations ..................................................................... 32.2. Material ............................................................................................................ 4
2.3. Element mesh quality criteria ........................................................................... 4
2.3.1. Principal stresses criterion ......................................................................... 4
2.3.2. Averaged/unaveraged stresses criterion ................................................... 4
3. Load cases and stress assessment..................................................................... 4
3.1. Torsion ............................................................................................................. 5
3.2. Bending ............................................................................................................ 6

-3-

1. General
The objective of the analysis described in this document is to substitute the analytical
calculation of the stress concentration factor (SCF) at the oil bore outlet with suitable
finite element method (FEM) calculated figures. The former method is based on
empirical formulae developed from strain gauge readings or photo-elasticity
measurements of various round bars. Because use of these formulae beyond any ofthe validity ranges can lead to erroneous results in either direction, the FEM-based
method is highly recommended.
The SCF calculated according to the rules set forth in this document is defined as theratio of FEM-calculated stresses to nominal stresses calculated analytically. In use inconnection with the present method in UR M53, principal stresses shall becalculated.
The analysis is to be conducted as linear elastic FE analysis, and unit loads ofappropriate magnitude are to be applied for all load cases.
It is advisable to check the element accuracy of the FE solver in use, e.g. bymodelling a simple geometry and comparing the FEM-obtained stresses with theanalytical solution.
A boundary element method (BEM) approach may be used instead of FEM.

2. Model requirements
The basic recommendations and assumptions for building of the FE-model arepresented in Subsection 2.1. The final FE-model must meet one of the criteria inSubsection 2.3.
2.1. Element mesh recommendations
For the mesh quality criteria to be met, construction of the FE model for theevaluation of stress concentration factors according to the following
recommendations is advised:o The model consists of one complete crank, from the main bearing centre line tothe opposite side‘s main bearing centre line.
o The following element types are used in the vicinity of the outlets:
10-node tetrahedral elements
8-node hexahedral elements
20-node hexahedral elementso The following mesh properties for the oil bore outlet are used:
Maximum element size a = r / 4 through the entire outlet fillet as well as in thebore direction (if 8-node hexahedral elements are used, even smaller
elements are required for meeting of the quality criterion)
Recommended manner for element size in the fillet depth direction
First layer’s thickness equal to element size of aSecond layer’s thickness equal to element size of 2a
Third -layer thickness equal to element size of 3a

-4o In general the rest of the crank should be suitable for numeric stability of thesolver.
o Drillings and holes for weight reduction have to be modelled.
Submodeling may be used as long as the software requirements are fulfilled.
2.2. Material
UR M53 does not consider material properties such as Young’s modulus (E) andPoisson’s ratio ( ). In the FE analysis these material parameters are required, as
primarily strain is calculated and stress is derived from strain through the use ofYoung’s modulus and Poisson’s ratio. Reliable values for material parameters haveto be used, either as quoted in the literature or measured from representative
material samples.
For steel the following is advised: E= 2.05·105 MPa

and=0.3.

2.3. Element mesh quality criteria
If the actual element mesh does not fulfil any of the following criteria in the area
examined for SCF evaluation, a second calculation, with a finer mesh is to beperformed.
2.3.1. Principal -stresses criterion
The quality of the mesh should be assured through checking of the stress component
normal to the surface of the oil bore outlet radius. With principal stresses 1, 2 and3 the following criterion must be met:
min

1,2,

3

0.03 max

1,2,3

2.3.2. Averaged/unaveraged -stresses criterion
The averaged/unaveraged –stresses criterion is based on observation of thediscontinuity of stress results over elements at the fillet for the calculation of the SCF:
Unaveraged nodal stress results calculated from each element connected to anodei should differ less than 5 % from the 100 % averaged nodal stress results
at this nodei at the location examined.

3. Load cases and assessment of stress
For substitution of the analytically determined SCF in UR M53, calculation shall be
performed for the following load cases.

-53.1. Torsion
The structure is loaded in pure torsion. The surface warp at the end faces of themodel is suppressed.
Torque is applied to the central node, on the crankshaft axis. This node acts as themaster node with six degrees of freedom, and is connected rigidly to all nodes of theend face.
The boundary and load conditions are valid for both in-line- and V- type engines.
yLoad:Torque T isapplied to thecentral nodexz

Boundaryconditions:
DOFs for allnodes are fully
constrained
u x,y,z = 0

Multi-point constraint:
All nodes of the crosssection are rigidly
connected to the central(=master) nodeFigure 3.1 Boundary and load conditions for the torsion load case.
For all nodes in an oil bore outlet, the principal stresses are obtained and themaximum value is taken for subsequent calculation of the SCF:
maxT

1,

2,

3N

where the nominal torsion stress
M53’s item 2.2.2 with torque T:

NTWPN

referred to the crankpin is evaluated per UR

-63.2. Bending
The structure is loaded in pure bending. The surface warp at the end faces of themodel is suppressed.
The bending moment is applied to the central node on the crankshaft axis. This nodeacts as the master node, with six degrees of freedom, and is connected rigidly to allnodes of the end face.
The boundary and load conditions are valid for both in-line- and V- type engines.
Load:
Bending by
moment M isapplied at thecentral node withrespect to oilbore outlet angle(see UR M53’sitem 2.1.1.2)

yxz

Multi-point constraint:
All nodes of the crosssection are rigidly
connected to the central(= master) node

Boundaryconditions:
DOFs for all
nodes arefully constrained
u x,y,z = 0

Figure 3.2. Boundary and load conditions for the pure bending load case.
For all nodes in the oil bore outlet, principal stresses are obtained and the maximum
value is taken for subsequent calculation of the SCF:
maxB

1,2,

3N

where the nominal bending stress N referred to the crankpin is calculated per UR
M53’s item 2.1.2.2 with bending moment M:

NMWe