Material
Function of welds
Static, dynamic(cyclically) loaded structure
Loading conditions
Fully loaded welds?
Working environment
Precision of the part - Distortion, inner tension
Productivity, Costs
On site, jobshop welding
On following figures answer
Function of welds - Static, dynamic loaded structure
Loading conditions
Working environment
Precision of the part
Productivity, Costs
Accessibility for welding-On site, jobshop welding
Welding process to be used
Material type
Code Requirements
Cost
To consider for design of Welded structure
No weld is best
Smaller better than big
Humidity, atmosphere is welders enemy
Think how the stress pass through structure
Simple rules for design of Welded structure
Load Failure mode Calculation
Static load Plastic deformation, Fracture, SCC
Ductile SHEAR failure
Re - Static safety coef. ,
Transition curves, SCC
Static, Dynamic,
Impact load
Fracture brittle
|Brittle TENSILE failure
Re –safety coef., CTOD,
Transition curves
Dynamic,
cyclical load
Fatigue – low, high cycle S-N (Wohler), Smith diagram
Thermodynamic
load
Creep Deformation -Time diagram
Wear
Corrosion SCC
1. calculation not needed
◦ Static load
◦ Full penetration butt weld: s=t
◦ Recommended size of fillet weld: a=0,7*t
◦ Well weldable material – S235
◦ Weld quality check done
2. Existing stress compared with stress limit
◦ Static, dynamic
3. Calculation acc. Codes, standards – EN
1993, AISI
4. FEM simulations
P/S=P/(2a*l)Double side weld
𝜏 = 𝐹/(𝑙 ∗ ℎ) 𝜏 = 𝐹/(𝑙 ∗ 𝑎)
σ 𝑟 =𝑀
𝐽∗r σ 𝑟 =
𝑀
𝐽∗r
𝜏 𝑟 =𝑀
𝐽∗ 𝑟
Combined stress state - Theory of plasticity
Τmax HMH theory
𝜎𝑟𝑒𝑑2 = 𝜎𝑐𝑜𝑚𝑏
2 + 4𝜏𝑐𝑜𝑚𝑏2 𝜎𝑟𝑒𝑑
2 = 𝜎𝑐𝑜𝑚𝑏2 + 3𝜏𝑐𝑜𝑚𝑏
2
Stress limit ◦ Based on Re reduced by safety factor (e.g. 1,5 - 3),
◦ MOST OFTEN allowable stress = Re/1.5
◦ or calculated from tensile strength
Tensile stress in notched specimenEqual tensile stress
𝜎𝑚𝑎𝑥 = 𝜎 ∗ 𝛼𝜎 = 𝐹/𝑆
Welds are non-homogenity in structure, welds
differ from WM in mictrostructure and stress
Possible is also presence of weld defects
Even if reaction of welded structure on outer force is
same as for non-welded structure, inner stress state
is significantly different
Good force transfer
High load capacity
Dynamic loading – full penetration weld
Difficult edge preparation
Load carrying in bending
Easy execution
a increase difficult
Risk of weld quench
Different strength of pipe branches for pressure vessels
A-risk of material delamination, easiest
C-the strongest, demands neck forming
Localized heating – uneven temperatures – heat cycle
Change of volume and mechanical properties with temperature
Lauwarmumformung von Stahl -
Mathias Liewald, Christian
Mletzko, Thorben Schieman
Localized heating
Thermal expansion
Decrease of mech properties
Material upsetting
Cooling
Thermal shinking
Increase of mechanical properties
Fixed Fixed
Distortion
Transversal
Longitudinal
Angular
Influence on distortion, stress
Weld size, length
Material – steel, stainless, Al
Weldment rigidity
Fixtures rigidity
Welding steps
Machining allowances
Heat treatment
Figure 29.11 Residual stresses developed during welding of a butt joint. Source:
American Welding Society.
Continuous welds - sealing
Intermittent welds – less distortion
Dynamic loading – root quality, ceramic
Rigidity x flexibility
ISO 13920 specifies 4 tolerance classes - A-D
linear, angular, and E-H for straightness, flatness,
parallelism
The tolerance class is indicated as ISO 13920-BE
Other tolerances can be indicated as well