The gist of the report was that the forces acting on the bolster are greater than the model indicated when fed with the network data. However during the investigation real world measurements have been made with sensor equipped 80X trains. It is these true measurements that have informed the new design.
It remains an open question as to what was wrong in the first instance - the model or the network data. This is something that needs to be resolved.
There is also a risk that the sensors are only as good as where they have been located. The forces transmit through the structure and in layman’s language bend or twist it if it is not strong and rigid.
If you start strengthening corner joints etc, you can make these stronger than other parts, and if not careful you move the problem. I always remember this being illustrated with a kitchen sponge, if you twist it, it bends all the way along, but if you clamp the ends so they are rigid and do same, then the movement is concentrated on a smaller area so that is more likely to tear now. Obviously same will now happen to the metal frame of the trains, if you strengthen one area and same forces are applied then the remainder gets more flexing force (force is concentrated over smaller length)
So clearly if the other parts were not specified with a large margin then there is more risk on the remainder of the frame. But we now know there wasn’t sufficient margin and parts cracked, and if no one has used sensors on a selectively strengthened frame, how can anyone know how the real world forces act on the remainder, if certain parts that were absorbing some of the force are now rigid and unable to absorb any movement.
This is a good point. Many years ago I was involved in investigating the reasons for a large number of broken springs on Vale Of Rheidol coaches when the line was owned by BR. The original springs were breaking and been replaced with new springs of a thicker section and instead of solving the problem the redesigned springs were also breaking. The reason for the failure of the redesign was that the springs had higher stresses as a result of the reduced movement allowed by the larger thickness. This had not been realised when the new springs were manufactured. The solution was to use a different steel to pretty much the original dimension.
Interesting thoughts. A case of moving the problem around and not addressing the basic cause. The least one can hope for is that the problem can be moved to components that are easily replaced. Now what would they be on a 80x ?.
Another twist. In this case could the stronger springs have pushed the problem onto less easily repaired/replaced components ?.
Of course, perish the thought, but maybe the permanent way needs to be kinder to the 80x ?. Are the culprits just a few rogue locations on the network ?. Not really the fault of the network of course and not a fault of the original spec it seems BUT maybe that is the cheaper solution overall ?.
Catching up with a few thoughts on this thread. [as an engineer not directly involved]. This is plenty in the public material when read carefully with an expert eye.
Problem stream A
1. At the design stage only new wheel sets were modelled with network rail data.
2. Recent on board measurement have shown new wheel set forces to be inline with modelling.
3. Worn (they don't directly specify just wear or potentially diameter reduction from wheel turning as well) reduced wheel sets were measured to exert higher forces than modelled. With the measured forces exceeding problematic levels in modelling.
4. NR track data realistic enough.
e.g. design/modelling fail
Problem stream B
5. Aim to standardise bogie designs across AT200 and AT300, including both low and high floor designs on the AT300.
6. Handle variation in floor height on AT300 using different damper brackets / suspension components with the unfortunate effect of increasing the loads in the problem areas on high floor vehicles (replacing the bogies on the high floor designs and having a lateral damper and anti roll bar mounting further above the ground level would help)
e.g. standardisation /cost reduction fail
Problem stream C
7. Choice of particular 7xxx series alloy
- Japanese developed alloy without a 7xxx ISO designation only manufactured in Japan, relatively new alloy only sold this century. Nearest ISO alloy is probably 7005 but still significant differences
- recent history of SCC issues and investigation research papers post 2016 on it (lots of Chinese authored papers) which suggests others are having issues.
- very little use out side Japanese specified products
- design choice optimisation of the alloy appeared to heavily focus on manufacturability over other parameters
8. Choice of T5 heat treatment regime
- makes manufacturing easier and substantially cheaper
- sub optimal choice for strength, fatigue, fracture toughness and SCC
- major questions over why not T6 with induction based solution heat treatment (else the same as T5)
- T5 is well known for increased SCC problems compared to alternatives
e.g. cost minimisation fail
Problem stream D
9. Mechanical design of bolster etc.
- includes several features with long history of enhancing fatigue issues (fix has learnt lesson here)
- failure to taper stiffness of structural elements in the design e.g. stiffness of solid bolster elements is much greater than largely hollow extrusions. Stiffness of "add on" elements needs to be tapered so there aren't large variation in stiffness at component extremities compared to bodyshell
10. Lack of attention to specifying fatigue reducing finishing in manufacturing.
e.g. design/modelling fail
Problem Stream E
11. Modern 2 pack paint systems can be very hard / stiff compared to traditional paint systems but many design engineers don't realise this. Work needs to be done to reach a sensible compromise on paint stiffness. This issue is also seen in composite structure so is not unique (see Airbus A350 issues).
12. Modern 2 pack paint systems need careful priming on aluminium which appear not to have happened
e.g. design fail
Problem Stream F (minor in comparisons to the others)
13. Not removing chlorine from problem areas regularly enough
e.g. maintenance regime (specification) failure
No single causes of problem but classic swiss cheese hole alignment
