Residual Strength Determination

Background

Residual strength is the load or cycles (usually mechanical) that a damaged structure or material can still carry without failing. This type of analysis requires an understanding of damage state in a given structure. The damage can be caused by in-service loading, such as introduction of micro-cracks in a composite panel, or damage and delamination in a panel when subjected to impact loading. The capability is critical for aerospace and infrastructure applications where post damage response is of great importance. For example, when fatigue causes a crack in an aircraft panel to grow in flight, residual strength analysis is crucial to determine how many more cycles can the aircraft sustain for safe landing assessment. Another example, what is the reduction in compressive strength of a stiffened panel after the panel is subjected to low velocity impact. Integrated computational simulation such as the one developed by AlphaSTAR, can be used to determine post damage reduction ins residual strength.

Objective

Provide analysts and designers with accurate computational simulation capability to determine residual strength following a specific damage event (example: tension after impact TAI, compression after impact CAI and shear after impact SAI, residual strength after discrete source damage in a stiffened panel of wing).

Approach

Use GENOA's multi-scale progressive failure analysis MS-PFA to determine all stages of damage evolution under service loading. Damage evolution comprises damage initiation and propagation (including delamination). MS-PFA is finite element based progressive failure analysis that augments traditional commercial FEA stress solvers for durability and damage tolerance. It allows the extraction of damage history for use in post-damage residual strength calculation.

Tools Used

Relevant GENOA modules are MS-PFA: static, fatigue, and impact (explicit). For example, low or high cycle fatigue analysis for a given number of cycles, then damage history is extracted from fatigue analysis for use in determining maxim static failure load (as typically done for aircraft panels or wing component).

Benefits Provided

Determine damage history under service loading.
Determine post damage residual strength including failure modes and failure location)
Answer what can be done to improve residual strength post damage
Evaluate and manage risk associated with certain damage events

Past Experience

Technology was applied successfully to determine post impact residual strength on coupon and element, and component level structures made polymer composites. Furthermore, it was applied to determine residual strength on wing structures after fatigue.