Improving Global Quality of Life

As another most important item, the prevailing stiffness (restraint intensity) in the repair area due to
surrounding assembly groups and the associated strain constraint are usually much higher than during
fabrication welding and have to be assessed before a repair welding procedure is carried out. For crackresistant
repair welding, knowledge of the stresses introduced by welding is of major importance, especially
when the repair welding procedure has to be carried out at a high shrinkage restraint. Since the research
efforts in welding have been concentrated on the respective materials and the development of new welding
procedures, investigation of the design aspects of repair welding probably represents a major target for
the near future. This involves correct and quantitative evaluation of shrinkage restraints for repair welds,
including the effects of the various joint types and reinforcements. With this respect, it has to be anticipated
that the intensity of restraint as a quantitative parameter to evaluate structural stiffness in the near and far
field of a joint will gain increasing importance. Additionally, a precise knowledge of the thermo-mechanical
effects of the repair welding procedure on the residual lifetime has to be elaborated.
It is also essential to determine the welding sequences with lowest possible likely stress-strain distribution
during and after the repair of steel structures. This will allow it to enlarge the available load spectrum for
later service. In this context, it has to be mentioned that interaction of concurrent repair welds has not been
understood up to the present time.
The failure resistance of a repair weld is also dependent on the applied filler materials and their transformation
behaviour depending on metallurgical, welding and heat treatment parameters. With respect to the repair
of steel structures and components, high-strength filler materials with correspondingly lowered martensite
transformation temperatures have to be developed further to achieve lower residual stresses in the repair
welding at respectively higher strength, i.e. service load capacities.
It has also to be mentioned that a series of downstream methods are available for reducing welding-specific
loads in repair joints or even for producing compressive residual stresses at the surface. Such technological
procedures, like stress relieving, shot peening, peening, ultrasonic treatment etc., are generally very timeconsuming
and costly and should be developed further regarding better applicability to repair welding.
It can only be emphasised that repair welding requires decent component weld tests, rational residual
stress evaluation and respective numerical calculations to achieve an actual increase in the life time of a
component or structure and to avoid further failure origins in the repaired parts.
4.4 Advanced design and structural integrity rules
Recent advances in joining technologies together with new materials bring increased attention to the damage
tolerance design, long service life and improved structural performance together with the developments in
structural integrity assessment rules (e.g. BS 7910, API 579, R6, FITNET FFS) for the load-bearing structures.
Recently, IIW Commission X has taken the task to develop IIW recommendations for the assessment of
structural integrity of welded structures by taking into account recent developments in this field. IIW FFS
Recommendations for Fracture Assessment of Weld Flaws (Doc. X-1637-08/Rev.3, Vol. I Procedure, Vol.
II Annex) document is now in its 3 rd revision and available as a working document.
For example, in the field of aircraft manufacturing of new welded integral airframe structures, specific “Local
Engineering” considerations in design and fabrication have potential for further improvements in local laser
weld joint properties. Established damage tolerance assessment rules for conventional (riveted) structures
may need to be further developed for welded integral airframe structures. Fatigue and fracture assessments
can be over-conservative with current methods and this in turn may act as a limiting factor for successful
implementation of advanced joining technologies in airframe manufacturing. Therefore, R&D efforts for better
understanding of failure mechanisms of joints, development and validation of testing, structural integrity
rules and hence an overall roadmap for LBW and FSW welded integral airframe structures are needed.
30 Improving Global Quality of Life Through Optimum Use and Innovation of Welding and Joining Technologies