9 Failure Diagrams

WF06: Create Failure Diagram

Pre-requisites:

• A. FBD Model: contains model items defined with functions
• B. SRA Module: access enables ability to edit Criticality parameters

Workflow steps:

1. Access Failure Diagram viewer — Select a model item and access 'Failure Diagram' viewer under 'Modeling' of main menu bar or via the right-click context menu opened on the model item.
2. Define FFM General Details (Display Name, Unit of Measurement, Initial Value, Internal Damping, Narratives) — Select a Functional Failure Mode (FFM), to define general details and narratives, in the 'General' tab of the Properties viewer.
3. Edit FFM Criticality Parameters (Difficulty of Detection, Probability/Occurrence, Severity, Is FFM a Failure?, Controllability, Probability/Exposure, Failure Mode Ratio, Failure Effect Probability) — Continue to the 'Criticality' tab of the Properties viewer and edit the Criticality parameters, for both low FFM and high FFM. Complete this for all FFMs of the model item.
4. Decision: Build Failure Diagram? — Build the failure diagram if necessary and if the physics of the failure are known.
5. Build Failure Diagram (Causes, Mechanisms, Faults, Failure Conditions, Losses/Symptoms, Display Name, Narrative) — Use the Failure Concepts Taxonomy Library to build Failure Diagrams, and where necessary, defining a display name and/or narrative in the 'General' tab of the Properties viewer.
6. Edit Fault Criticality Parameters (Difficulty of Detection, Probability/Occurrence, Controllability, Probability/Exposure, Failure Mode Ratio, Failure Effect Probability) — For all faults, open 'Criticality' tab of Properties viewer and edit Criticality parameters.
7. Edit Connection Criticality Parameters (Causal Probability, Progression Rate, Polarity, Causal Strength) — Edit Criticality parameters for the connections between the failure concepts of the failure diagram.
8. Failure Diagram Created — Failure diagrams created for selected model item.

9.1 Assign Functional Failures

When modelling concept designs that have not yet defined solution-specific components, failure responses can be assigned to a generic component based on the expected response of its functional outputs, without having to reference physical processes of failure or hardware degradation.

To assign Functional failures to a component:

• Select (left click) a component and ensure the Properties viewer is opened
• From the Properties viewer, select the Functional Failures tab
• Ensure the Override Failure Diagram? checkbox is checked
• Select failure response/s (high or low) to be considered for each functional failure mode

Example: a hypothetical failure response of the Fuel Tank has been activated in the Functional Failures tab. In this case, it is assumed that any failure of the tank will lead to loss of fuel, but since the tank itself cannot generate extra fuel, Static Pressure High response has been deactivated — the properties table shows Functions & Flow Properties = "Provide > Liquid Static pressure", with Increase (High) unchecked and Decrease (Low) checked.

Note for Functional Failures: When there are no Failure Diagrams created for a component or failure diagrams are disconnected from the functional failure mode, the Override Failure-Diagram check-box is disabled (greyed-out). This means that Functional Failures are automatically enabled for the component. Example: the Air Filter's "Refine > Gas Mass flow rate" functional failure shows both High and Low checked and enabled by default because no failure diagram exists for it yet.

9.2 Create a Component Failure Diagram

The failure diagram maps out the sequence of events leading to an item's functional failure mode. This graphical representation shows a chain of causes, mechanisms and faults that lead to a functional failure mode and is used to inject faults into the system during failure simulation or failure mode, effects & criticality analysis (FMECA). Definitions for failure causes, mechanisms, faults, symptoms and functional failure modes can be found in the Help Glossary.

To open a component failure diagram:

• Select (Right-click) an item (component, part or pair) in the system model
• Select Failure Diagram from the right-click menu

When the failure diagram editor is opened, the user will find a circular icon representing the component functional failure mode (output flow property) will be displayed. This icon cannot be removed or changed unless the function, flow and flow property of the item in the Function editor is removed or modified.

Trivalent thresholding is the default failure simulation threshold set in MADE. This threshold type assigns three possible states to a functional failure mode (FFM):

1. Low (Flow fails Low)
2. Nominal (Flow is Nominal)
3. High (Flow fails High)

To determine whether the outcome of a failure mode results in one of these failure states during analysis, the failure path (i.e. sequence of events) leading to a FFM must first be mapped out in the failure diagram. This is done by connecting failure causes, mechanisms and faults to the FFM. Failure concepts are defined in MADE using a standardized taxonomy of failure concepts.

9.2.1 Adding Failure Concepts to a Failure Diagram

Failure concepts can be found in the Failure Concepts viewer on the left side of the screen. Alternatively, the viewer can be accessed by selecting Windows → Open View → Failure Concepts from the main menu. Failure concepts are found by browsing sub-folders (Assembly and reassembly, Design, Maintenance, Manufacturing, Operation, Transportation) or using the search field at the top of the viewer.

A drop-down menu allows filters to sort failure concepts into broad categories:

• Electrical
• Mechanical
• Plastics
• Software

(An additional checkable "Auto Design" option also appears in this same drop-down — see 9.2.2.)

Note for Incipient Faults: Incipient Faults (e.g. Buckling) are located on the tooltip when the user places the cursor over a fault to view the tooltip.

Placing the cursor over each Failure Concept will also display a tooltip showing its name, category, sub-category (if applicable) and description. Example: hovering over "Corrosive attack" (under category Corrosion) shows: "Name: Corrosive attack. Category: Corrosion. Synonym: Caustic attack, oxygen pitting, hydrogen damage, acid attack, chemical attack."

The Failure Concepts icon legend at the top of the viewer distinguishes: Cause (blue downward triangle), Mechanism (green diamond), Fault (red "no entry" circle), Failure Condition (black icon), Symptom (brown icon).

9.2.2 Adding Auto-Design Failure Concepts

An additional option called Auto-design enables users to drag out complete failure tree diagrams (connected Causes, Mechanisms & Faults) when dragging out a Failure Mechanism.

To enable Auto Design:

• Select the drop-down icon in the Failure Concepts viewer
• Select Auto Design (verify that a checkmark is visible next to it – this means it is enabled)

To assign a failure concept or failure tree diagram to a component, part or part-pair:

• Open a component failure diagram (right-click item in system model)
• Select the Mechanism Failure Concept category (green diamond)
• Use the search field or browse through the categories for a failure concept
• Select (left click) a Failure Concept
• Drag the concept onto the failure diagram editor
• Select (left click) and drag a Fault to connect it to a Failure diagram

Example: adding the Corrosive Attack mechanism with auto-design enabled displays a connected tree in the failure diagram with Causes "Untimely maintenance actions", "Insufficient cleaning", "Corrosive contaminant", "Damaged surface protection" feeding into Mechanism "Corrosive attack", which feeds into Faults "Pitted", "Corroded", "Perforated". The failure diagram is completed by connecting the faults to the FFM ("Refine Gas Mass flow rate").

FFMs can be connected from the faults of the Failure tree diagram to represent multiple failure paths leading to the component failure mode — e.g. Failure Path 1 (via "Pitted"), Failure Path 2 (via "Corroded"), Failure Path 3 (via "Perforated"), all converging on the FFM "Refine Gas Mass flow rate (Air Filter)".

9.2.3 Adding Custom Failure Concepts

If automatic failure tree generation has not produced the desired fault tree, manual customization can be performed. The prescribed order of failure concepts to create a failure path is as follows:

Cause(s) → Mechanism(s) → Fault(s) → Functional Failure Mode(s) & Symptom(s)

To delete any unwanted failure concepts:

• Select (left click & drag) one or more failure concepts
• Select (right click) and select Delete from the right-click menu

9.2.4 Add New Failure Concepts to Existing Failure Trees

Failure paths define the relationship between failure concepts leading into an item FFM. These paths are necessary for the generation of Functional Fault Trees during Fault Tree Analysis. Similarly, during system-wide failure simulations (propagation analyses), each failure path is automatically mapped – the level of complexity of failure paths in the system is entirely dependent on the amount of detail provided in the item failure diagrams.

To add & connect a new failure concept to an existing failure tree:

• Select (left click) and drag a failure concept into the failure diagram editor
• Select (left click) the failure concept and drag the arrow to the next concept
  • Method 1: Select the Failure Connection Icon from the Icon Menu and click-and-drag from one failure concept to the next. A plug symbol will indicate whether a causal connection is possible or cannot be achieved due to a conflict in the order of failure concepts (e.g. connecting "Damaged surface protection" directly to a Fault "Perforated" is blocked with a "no entry" icon, since a Cause cannot connect directly to a Fault, skipping the Mechanism).
  • Method 2: Drag-and-drop the selected failure concept on another failure concept in the Failure Diagram editor. This will automatically connect both failure concepts. Example: dragging "Untimely maintenance actions" onto "Damaged surface protection" (both Causes feeding an unconnected Mechanism placeholder "Solid particle contaminants") automatically wires the connection and the Mechanism becomes "Corrosive attack", now fed by all three causes: Damaged surface protection, Untimely maintenance actions, Solid particle contaminants.

9.2.5 Creating AND & OR Gates

The Failure Diagram editor provides AND & OR gates for conditional connections between causes and mechanisms. AND gates are used when two or more failure causes are necessary to initiate a failure path leading to a failure mechanism; OR gates are used to define individual failure paths when more than one cause is connected to a mechanism.

To create an AND gate:

• Select (Right-click) a failure Mechanism from the failure diagram editor.
• Select New → AND Gate from the right-click menu.
• Connect Failure Causes to the AND gate.

To create an OR gate:

• Link a single, unconnected Failure Cause directly to a failure mechanism.
• An OR gate will be automatically assigned to the newly connected failure cause.

9.2.6 Editing a Failure Connection between Failure Concepts

The impact of the failure path on the output flow property is defined by the criticality factors and polarity of failure concepts and the failure connections between them. After a failure path or diagram is defined, its criticality factors and/or polarities should be edited to prioritize failure paths in a FMECA.

To edit a failure connection:

• Select (Left-click) a failure concept or failure connection
• Open the Properties Viewer
• Edit the displayed factors using the slider or numerical entry field

The criticality tab is context-sensitive and will change according to the failure concept or failure connection selected in the failure diagram. The table below shows the list of fields shown for the type of failure concept selected and the tab selected in the Properties viewer.

Note on the Reliability tab: The Reliability tab is only displayed in the RAM Module. The impact of these variables will be investigated in more detail in the RAM module user manual.

Table 3: Description of Failure Concepts and Connection tabs in the Properties view

Failure Concept¹ / Failure Connection²	Properties view Tab	Descriptions, Editable* Fields, Sliders or Toggles
Cause¹	General	Name, Category, Sub-Category, Description, Narrative*
Cause → Mechanism²	General	Source (Cause), Target (Mechanism)
	Criticality	Probability*
Mechanism¹	General	Name, Category, Sub-Category, Description, Narrative*
Mechanism → Fault²	General	Source (Cause), Target (Mechanism)
	Criticality	Probability*, Progression*
Fault¹	General	Name, Category, Sub-Category, Description, Narrative*
	Failure Conditions	Failure Conditions*, Narrative*
	Criticality	Difficulty of Detection*, Occurrence*
	Number	Failure Mode Ratio*, Failure Effect Probability*
	Reliability	Failure Mode Ratio*
Fault → Failure Mode²	General	Source (Fault), Target (Functional Failure Mode), Function, Polarity*, Causal Strength*
	Criticality	Probability*
Fault → Symptom²	General	Source (Fault), Target (Symptom)
Symptoms¹	General	Name, Category, Sub-Category, Description, Narrative*
Failure Mode¹	General	Display Name*, Flow Property, Function, Measurement Unit*, Initial Value*, Weight Coefficient*
	Narrative (High/Low)	Cause, Response Narrative, Remarks, Detection Method
	Criticality (High/Low)	Difficulty of Detection*, Occurrence*, Severity*, Is Failure (Yes/No)*
	Number (High/Low)	Failure Mode Ratio*, Failure Effect Probability*
	Reliability (High/Low)	Failure Mode Ratio*, Is Failure (Yes/No)*

Example connection edited: a "Biological corrosion" cause node — General tab shows Name = "Biological corrosion", Category = "Corrosion", Description = "Corrosive attack from the waste products of living organisms."