Tomasz Wojcik

2024-10

Shock loading analysis of electronics chassis — simulated pyroshock event using modal transient analysis (Abaqus Standard) from measured shock spectrum input. Validated against test SRS data.

Challenge: Converting a test-measured SRS into a time history input for Abaqus required synthesizing a time domain signal that reproduces the SRS. Standard SRS synthesis methods (wavelets) gave poor agreement below 100 Hz.

Learned: SRS synthesis is a known difficult problem — multiple time histories can produce the same SRS. The synthesized signal must also have realistic duration and temporal characteristics, not just match the SRS envelope.

2024-05

Hail impact analysis on composite nacelle panel — 30mm ice sphere impact at 60 m/s, progressive damage with Hashin criterion, post-impact residual strength assessment.

Challenge: Ice material model (elastic brittle with tensile failure) was numerically unstable at impact. Replaced brittle failure with a crushable foam material model (Abaqus) with carefully calibrated volumetric hardening — gives physically reasonable energy dissipation without numerical instability.

Learned: Ice in impact simulations is numerically challenging. The brittle failure model leads to explosive element deletion and mass loss. Crushable foam analogy with appropriate energy absorption calibration is more stable and equally accurate for the structural response.

2023-12

Blade-off containment analysis per FAR 33.94 — rotating fan blade fragment released at maximum speed, impacting containment ring at highest kinetic energy. Assessed ring deformation and fragment capture.

Challenge: Rotating the blade in Abaqus Explicit requires prestress from the spinning state (centrifugal loading) before the impact event. The prestressed initial state had to be imported from an Abaqus Standard static analysis — ODB import with SIGINI not straightforward.

Learned: For rotating impact problems, the prestress from centrifugal and thermal loads significantly affects the blade fragment's post-release behavior. Neglecting it gives non-conservative predictions for fragment energy and trajectory.

2023-08

Equipment drop test simulation — avionics box dropped from 1.2m on steel plate. Rigid body rotation before impact, elastic-plastic deformation of housing, acceleration time history at mounting interface.

Challenge: Contact between the box corner (sharp edge) and rigid floor caused severe hourglassing in the element directly at the contact point. Selective reduced integration with enhanced hourglass control resolved the numerical instability.

Learned: Sharp corner contacts in explicit dynamics often trigger hourglassing. Strategies: finer mesh at contact, enhanced hourglass control, or small geometric radius on the contact feature. Do not simply increase the hourglass coefficient — that artificially stiffens the response.

2023-02

Bird strike simulation on engine fan blade per FAR 33.76 — bird modeled as a fluid-like projectile using SPH (Smoothed Particle Hydrodynamics), blade modeled with CFRP progressive damage (Hashin). Assessed blade failure and energy absorption.

Challenge: SPH bird model requires careful calibration of Murnaghan equation of state parameters against Hugoniot test data. Default Abaqus bird material parameters (from literature) overestimated impact load by ~25% vs test. Calibrated using GE internal bird strike test database.

Learned: SPH bird material model accuracy is crucial — the impact load determines everything downstream. Always calibrate against test data for the bird mass and impact velocity range of interest. Do not rely on generic literature parameters for certification analyses.