Input Data for Computational Welding Mechanics
This section describes the author’s preferred input data for a Computational Welding Mechanics analysis of a welded structure. Often some desired input data will not be available. In that case one must use the best available approximation that one can find. In addition, one can do analyses with different values of uncertain data in an attempt to bracket the most probable behavior.
The structure to be welded has a set of parts. Each part has geometry and a material type, e. g., HSLA x80 steel. (Initial conditions for the thermal, microstructure and stress analysis are discussed with each solver.). The geometry of each part can be defined by a stereolithographic (STL) file generated by a CAD system or by a parameterized object. For example, a straight pipe can be parameterized by the values of the end points of the axis and its inner or outer radius and wall thickness. Each parameterized object requires a set of parameter names, values and dimensions. For example, ((part Type pipe) (start Point (jc, , z,) meters), (end Point
(x2y2,z2) meters), (outer Diameter 0.6 meters), (wall thickness 6.2
mm)). Any object that can be parameterized, can be defined by such a list of parameters specified by names, values and dimensions.
When generating STL files from a CAD system, options should be chosen so that the CAD system preserves the position of the STL file for the part in space.
Each weld joint has “ribbon” that defines a curvilinear coordinate system along which the weld procedure is swept. The ribbon could be represented as an ordered set of pairs of points that represents two flow lines that have a start point, end point and hence imply an oriented distance along the ribbon.
Each weld joint has a weld procedure to be described below. A weld procedure can describe a multipass weld.
The order of each weld pass must be specified, i. e., its start time and start position and either or both its end position or direction. We prefer to specify time by year month day hour minute second. For example, 20031104.134522 the year is 2003, the month November, the day 4th, the hour 13, the minute 45 and the second 22. We prefer both welding direction and weld pass end position because it provides a redundancy that can be checked for consistency. A circular weld that starts and ends at the same point must specify a welding direction, e. g., positive or negative direction.
The geometry of fixtures must be defined. Fixtures can either be rigid or compliant. If compliant, the material type of the fixture or its Young’s modulus and Poisson’s ratio must be specified. This can usually be done simply by specifying the alloy type of the fixture. If the fixture is compliant, the fixture itself usually must be constrained in some way to resist loads. The contact condition between the structure being welded and the fixture must be specified. It could be a contact element that is very stiff in compression and very soft in tension. If the structure is supported by soil, then the soil could be considered a fixture. Soil could have an appropriate constitutive model, such as a CAP model. The soil constitutive model is a function of the soil type, i. e., sand, clay, etc.
The direction of gravity must be defined for this structure, e. g., (0,-9.8, 0) means that +y is vertically up.
The environment in which welding is being done should be specified. Examples include air, velocity (wind) (vx, vy, vz), temperature 20°C, pressure 1 bar, humidity 80%. For underwater welding, air would be replaced by water.
Some parts of the structure could have a special environment, e. g., a pressurized natural gas pipeline could specify the internal environment by methane, velocity (vx, vv, vz) or flow rate kg/s or m3/s, temperature 20°C, pressure 60 bar.