This review is a compilation of several reviewers from ORE Catapult.

• Lines 70 - 80 there is a repetition of 'As the proposed approach can be used for any load direction, it enables target loads for any fatigue test method including biaxial testing. ' 

•  Figure 1 is a good way of showing the different approaches. 

• Equations 2 and 3 needn't be used, there is a matrix formulation approach which can use an arbitrary reference line and the appropriate 'bending and axial' 3 x 3 sub-matrix of the 6 x 6 section matrix to calculate strain given loads defined at an arbitrary reference point/axis. If everything is done correctly, the two approaches will give the same result so the way described in the paper is valid but not the only way (having finished the review, I now see this is addressed very well in the appendices). 

• Line 250 - that's a lot of steps! 

•  Line 265, section 3.1. This is an interesting comparison - I'm not sure our customers would agree that 1.8% is negligible, but with our damage-based approach (which from experience of discussing this with OEMs seems to be how it is done when confidentiality is not an issue, ie. in-house) the test load (where we can't control Fz) is just increased so that the damage (which is only really coming from Mx and My loading in the test) is matching the service life damage (coming from Mx, My and Fz loading).  

•  This approach is good because it has the advantage of needing less customer data, and I suppose material properties for UD carbon, glass and biax and triax are available in the OPTIDAT database to get the UTS and UCS for all the common material types you'd see in the blade. The disadvantage is that you can't consider the 3 R-value diagram - when we do fatigue analyses we frequently see that carbon fails unless you can account for the very high values of m in the SN curve for compressive loading. Our test load derivation essentially continues on path 3.2 to iterate to find loads which do the same amount of damage for each cross section of blade. 

•  Figures 3 and 4, nice plots :) 

•  Figure 5 and 6 do a very nice job of showing why IEC 61400-23 needed to move away from DELs to a damage based approach. 

•  ...and Figures 7 and 8 do a very nice job of showing why bi-axial testing is so important.  

• Line 330- add text to draw attention to the criticality of the regions missed. Along the lines of “The hatched area includes features which should be tested such as critical structural details and significant load transitions between design elements. “ 

•  Line 340 -change “magnificent”, could be changed to either significant or magnified. 

• The appendices do a very good job of defending some commonplace assumptions about the strain derivation from test loading. 

• Line 353. Perhaps the conclusion could make reference to the different streams laid out in the flow diagram in fig 1. 

• Figure 1: “sweep” is used, as well as in line 114, I think these have 2 different meanings, but its not clear. 

• Fig 3 and Fig 4 – do these relate to the streams labelled in the flow diagram? If so, they could be included in the caption. 

Overall, the paper is making a great argument for a damage-based approach to testing, which is obviously what is going to become the norm going forwards with the new release of IEC 61400-23.