Impact Simulation Through Progressive Failure Dynamic Analysis
|Soft Body Impact Simulation|
Copyright J. Bayandor, CRASH Lab, Virginia Tech
Composite automotive and aerospace structures are subjected to various
types of impact loading in service. The impact loading can be characterized into two categories:
low and high velocity. The ability to accurately design for impact is key to the reliability
and safe operation of the product or structure. AlphaSTAR developed and validated analytical
simulation methods for assessing impact resistance characteristics of composite structures.
The capability is suitable for modeling: automotive crush and crash events; impact and post-impact
residual strength assessment under tension, compression, or shear; hail impact on aerospace
structures, and for bird strike analysis and certification.
Assessing composite or sandwich structures damage under impact loading is challenging
as it requires integration of explicit dynamic finite element solution with damage tracking
and fracture. The loading is usually in perpendicular direction to the main axis of structure
exhibiting different failure mechanisms as compared to those experienced under static loading.
Other challenges stem from determination of strain rate effect on material properties. Traditional
methods are capable of assessing peak load but lack when it comes to simulating the failure
process observed in test.
Most analytical models are adjusted to replicate test behavior, especially for high velocity
impact. (i.e. bird strike simulation). The challenge is to provide a priori prediction of test
behavior rather than just duplicate test behavior, especially in high strain and deformation
fields. The focus of AlphaSTAR is to provide engineers with a reliable tool for assessing behavior
of structures under all types of impact loading.
Relying on test alone to design for impact loading compromises the durability,
reliability, integrity, and operational safety of the structure. This lead to an increase in
weight to account for scatter in impact conditions under service.
How we address it
By use of multi-scale based progressive failure analysis integrated with explicit
dynamic finite element solution. Most explicit finite element analysis (FEA) solvers assess
damage at the lamina level whereby damage initiates at lower scale in the fiber, matrix, and
GENOA Progressive Failure Dynamic Analysis PFDA augments Explicit Dynamics (ED) finite element
analysis with multi-scale composite mechanics, and damage tracking and fracture to determine
all stages of damage evolution under impact, crush, or crash loading condition. The methodology
determines conditions for damage/delamination initiation and growth to fracture. The damage
tracking is done by identifying and accumulating damage at the "root cause" of the composite
in matrix and fiber using dedicated physics based damage and failure criteria. PFDA calculates
crack density, micro-cracks in the matrix, delamination within the plies, and fiber failure
in tension and compression including micro-buckling.
Capture damage and fracture evolution process under impact loading.
Determine how failure occurs and how to fix it.
Reduce number of tests by relying on accurate analysis and simulation methods.
Eliminate unnecessary increase in weight by determining the residual strength post impact.
Increased durability and reliability.
Inclusion of material properties due to high strain rate effect.