Apparatus with damage indication feature
A method of designing and manufacturing apparatus. The method comprises: creating a design space; analysing expected loads acting on the design space to calculate a first load path within the design space; analysing expected loads acting on the design space when the apparatus is in a damaged state to calculate a second load path within the design space; selecting a region of the second load path which falls outside the first load path; and creating a final design which includes: a primary structure falling within the first load path; and a damage indication feature falling within the selected region. The damage indication feature is designed to provide a visual indication when the load transmitted by the damage indication feature exceeds a threshold. The load generates a stress in the primary structure which exceeds the stress in the damage indication feature until the primary structure becomes damaged, at which point the load generates a stress in the damage indication feature which exceeds the stress in the primary structure.
1. Apparatus for transmitting load, the apparatus comprising:
a. a primary structure designed to transmit the load via a primary load path; and
b. a damage indication feature which is positioned outside the primary load path and is designed to transmit at least a portion of the load only after the primary structure has become damaged, the damage indication feature being designed to provide a visual indication when the load transmitted by the damage indication feature exceeds a threshold and before the damage in the primary structure causes a critical failure of the primary structure;
wherein the load generates a stress in the primary structure which exceeds the stress in the damage indication feature until the primary structure becomes sufficiently damaged, at which point the load generates a stress in the damage indication feature which exceeds the stress in the primary structure.
2. The apparatus of claim 1 wherein the damage indication feature has a maximum dimension which is lower than a minimum dimension of the primary structure.
3. The apparatus of claim 1 wherein the damage indication feature comprises an elongate strut extending across a gap between a pair of opposing elements in the primary structure.
4. The apparatus of claim 1 wherein the damage indication feature is designed to crack, rupture or deform plastically when the load transmitted by the damage indication feature exceeds a threshold.
5. The apparatus of claim 1 wherein the damage indication feature and the primary structure are formed as a single piece.
6. The apparatus of claim 5 wherein the damage indication feature and the primary structure are formed as a single piece by additive fabrication.
7. An aircraft comprising the apparatus of claim 1 .
8. The aircraft of claim 7 , wherein the load is generated by a spectrum of forces acting on the aircraft.
9. A method of indicating damage to a primary structure, the method comprising:
a. transmitting load via a first load path in the primary structure when the primary structure is in an un-damaged state; and
b. transmitting load via a different second load path after the primary structure has become damaged, the second load path including a damage indication feature which provides a visual indication when the load transmitted by the damage indication feature exceeds a threshold and before the damage in the primary structure causes a critical failure of the primary structure;
wherein during step a. the load generates a stress in the primary structure which exceeds the stress in the damage indication feature, and during step b. the load generates a stress in the damage indication feature which exceeds the stress in the primary structure.
10. A method of inspecting the apparatus of claim 1 for damage, the method comprising inspecting the damage indication feature for a visual indication that the load transmitted by the damage indication feature has exceeded a threshold.
11. A method of designing the apparatus of claim 1 , the method comprising:
a. creating a design space;
b. analysing expected loads acting on the design space when the apparatus is in an undamaged state to calculate a first load path within the design space;
c. analysing expected loads acting on the design space when the apparatus is in a damaged state to calculate a second load path within the design space;
d. selecting a region of the second load path which falls outside the first load path; and
e. creating a final design which includes:
i. a primary structure falling within the first load path; and
ii. a damage indication feature falling within the region selected in step d., the damage indication feature being designed to provide a visual indication when the load transmitted by the damage indication feature exceeds a threshold.
12. A method of manufacturing the apparatus of claim 1 , the method comprising designing the apparatus by the method of claim 11 ; and manufacturing the apparatus according to the final design created in step e.
13. Apparatus manufactured by the method of claim 12 .