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TRANSCRIPT
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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
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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
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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
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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
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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
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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
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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
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Tensile stress in notched specimenEqual tensile stress
𝜎𝑚𝑎𝑥 = 𝜎 ∗ 𝛼𝜎 = 𝐹/𝑆
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Welds are non-homogenity in structure, welds
differ from WM in mictrostructure and stress
Possible is also presence of weld defects
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Even if reaction of welded structure on outer force is
same as for non-welded structure, inner stress state
is significantly different
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Good force transfer
High load capacity
Dynamic loading – full penetration weld
Difficult edge preparation
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Load carrying in bending
Easy execution
a increase difficult
Risk of weld quench
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Different strength of pipe branches for pressure vessels
A-risk of material delamination, easiest
C-the strongest, demands neck forming
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Localized heating – uneven temperatures – heat cycle
Change of volume and mechanical properties with temperature
Lauwarmumformung von Stahl -
Mathias Liewald, Christian
Mletzko, Thorben Schieman
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Localized heating
Thermal expansion
Decrease of mech properties
Material upsetting
Cooling
Thermal shinking
Increase of mechanical properties
Fixed Fixed
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Distortion
Transversal
Longitudinal
Angular
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Influence on distortion, stress
Weld size, length
Material – steel, stainless, Al
Weldment rigidity
Fixtures rigidity
Welding steps
Machining allowances
Heat treatment
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Figure 29.11 Residual stresses developed during welding of a butt joint. Source:
American Welding Society.
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Continuous welds - sealing
Intermittent welds – less distortion
Dynamic loading – root quality, ceramic
Rigidity x flexibility
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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