Material -...

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