9.3 Create Part Failure Diagrams

For components containing additional detail in the form of parts and part-pairs, part failure diagrams can be constructed and connected to the component FFM. Part failure diagrams are constructed in a similar manner to component failure modes with the exception that the failure path ends at a fault. This is because parts do not fulfil a function until they are connected to another part. Together, two parts form a pair whose function can then be defined.

Example: the "Lining" part failure diagram (left editor) shows Causes "Damaged surface protection", "Corrosive contaminant", "Untimely maintenance actions" feeding Mechanism "Corrosive attack [Inner Surface]", feeding Faults "Corroded", "Pitted", "Perforated" — ending at faults (no FFM, since a lone part has no function). The corresponding "Inlet_Lining" part-pair failure diagram (right editor) nests this same part failure tree inside an "Inlet" / "Lining" grey box pairing, with the faults connected via OR-gate weightings down to the pair FFM "Contain Liquid Flow rate (Inlet_Lining)".

Each part's Characteristics/Environment/Features summary is shown alongside the failure diagram, e.g. for "Lining": Environment = Corrosive Environment (× 3 entries); Characteristics = Loading Type(s): Internal Pressure, Loading Factor: Transient Load, Time Factor: Low, Operating Temperature: Medium, Operating Temperature Factor: Steady; Features = Inner Surface.

9.4 Create Part-Pair Failure Diagrams

Part-Pairs contain the Functional Failure mode of two connected parts in its Failure Diagram. Part Failure Trees are connected to the pair FFM which connect the failure path from part-level to part-pair level. Failure concepts can also be defined for the part-pair (known as pair-specific failure concepts).

9.4.1 Opening a Pair Failure Diagram

• Select (Right-click) the part-pair icon on the pair connection in the system model
• Select Failure Diagram from the right click menu

Two grey boxes inside the pair diagram represent the failure diagram of the two parts that form the pair.

To open a part failure diagram from within the pair failure diagram:

• Click on the plus symbol on the top-right of the part failure diagram box

Example: clicking the plus icon on the "Lining" grey box within the "Inlet_Lining" pair diagram expands it to reveal a Fault "Secure Solid Shape (Inlet_Lining)".

9.4.2 Create a Part-Pair Failure Connection (Failure Path)

• Open a pair failure diagram
• Expand a part failure diagram from within the pair failure diagram
• Select (Left-click) a part fault
• Drag the connection to the Pair Functional Failure Mode

Example: within the expanded "Lining" box, Causes "Untimely maintenance actions", "Damaged surface protection", "Corrosive contaminant", "Insufficient cleaning" feed Mechanism "Corrosive attack [Inner Surface]", feeding Faults "Pitted", "Perforated", "Corroded" — each connected via OR-gate ("−") weighted links, alongside the sibling "Inlet" part box, down to the pair FFM "Contain Liquid Flow rate (Inlet_Lining)".

9.4.3 Create a Pair-Specific Failure Diagram

Certain failure concepts apply specifically to the interaction between two parts, rather than to individual parts – a failure tree diagram must then be generated to describe the failure of a part-pair.

To generate a pair-specific failure diagram:

• Open a pair failure diagram
• Insert the required mechanisms, causes, faults and symptoms
• Connect the failure concepts in order
• Connect the Faults to the part-pair FFM to complete the failure path

Example ("Pair-Specific Failure Path connected to the part-pair FFM"): Causes "Cyclic mechanical loads", "Imbalanced mechanical loads", "Vibration loading" (all for "Inlet_Lining") feed an AND-gate into Mechanism "High cycle fatigue (Inlet_Lining)", feeding Fault "Fractured (Inlet_Lining)", which connects (alongside the "Inlet" and "Lining" part-level grey boxes, each contributing their own OR-gate weighted paths) into the pair FFM "Contain Liquid Flow rate (Inlet_Lining)".

Currently, the Failure Diagram is limited to using cut or copy actions (no drag-and-drop) to transfer failure concepts from one item to another e.g. a Fault from a part to a part-pair failure diagram.

To transfer failure concepts between Failure Diagram editors:

• Select (Right-click) a failure concept
• Select Copy or Cut from the right-click menu options
• Open the desired failure diagram editor to place the copied/cut failure concept
• Select (Right-click) the system model of the failure diagram editor
• Select Paste from the right-click menu options

9.4.4 Connect Pair-Component Failure Modes

To complete the failure path from part to pair and to component, the pair functional failure mode (FFM) must be linked to the component failure mode. Once this connection has been established, a positive polarity is assigned to show a directly proportional influence. For example, if the bolt-coupling part pair fails to transmit rotational angular velocity (pair FFM), then this will cause a reduction in rotational angular velocity (component FFM).

To connect the part-pair FFM to the component FFM:

• Open the component failure diagram
• Expand the part-pair grey box
• Select (left click) and drag from the pair FFM
• Drag failure connection to the component failure mode icon

Example ("Connecting a Pair FFM to a Component FFM in the Failure Diagram"): a "Lining_Outlet" pair-level grey box (containing "Lining" and "Outlet" part boxes feeding an OR-gate into pair FFM "Supply Liquid Static pressure (Lining_Outlet)") is connected (positive polarity, "+") along with a sibling "Inlet_Lining" pair-level box (also feeding via positive polarity) into the component-level FFM "Provide Liquid Static pressure (Fuel Tank)".