Course Length: 5 days

Pre Requisites:

Mathematical skills in matrix algebra and familiarity with engineering stress and strain concepts are required. Some knowledge of composite materials technology is helpful, but not required. Either M-1/R-1 or E-1 courses are suggested to provide suitable materials background if deemed necessary by the student.

Summary:

This course is designed for degree-qualified aerospace and mechanical engineers, or persons having practical experience in strength of materials calculations, that are responsible for the design analysis and substantiation of repairs to primary and secondary composite structures.

E-3 was developed with no firm prerequisite to provide commercial and military aircraft “repair” engineers with a fundamental level understanding of composite materials & processes (40%) and repair analysis (40%), in order to substantiate damage to a typical composite aircraft structure.Additionally, E-3 is 20% hands-on coupon testing to further provide engineers with the experience of fabricating a composite panel, performing a repair, and pulling test coupons.The E-3 course is optimal for repairs developed for surface panels, flight controls, wing-to-body fairings, landing gear doors, etc.

The E-3 course is prerequisite for the E-10 Advanced Aerospace Repair Analysis and Substantiation course.

Introduction:

In the aerospace world, composite repairs are most often performed in accordance with approved repair instructions. When the damage size falls outside the scope of these instructions, then the repair has to be individually analyzed and engineered for the specific structure. Just as important, the repair design has to be carefully substantiated to the appropriate authorities for final approval to proceed with the physical repair.

This course will provide attendees with the necessary skills in analyzing structural integrity loss, repair design development, and the mathematical analysis techniques and documentation needed to substantiate the repair to the satisfaction of the regulatory authorities, such as the FAA. Computer analysis is combined with hands-on coupon fabrication and repair testing for comparison.

Students will learn how to determine the type of repair required, analyze load transfer across the repair joints, determine the type of repair joints required (i.e.: taper-scarfed, stepped, bonded doublers, bolted doublers, etc.) and prepare the specific repair instructions.

This course also reviews the basis of strength calculations in composite materials and discusses several common “failure criteria” methods widely used in the industry.

A significant portion of the course will be devoted to repair documentation and validation techniques, and the types of information needed to substantiate the repair to regulatory authorities. While the emphasis in this area will be on substantiation to meet FAA requirements, the same types of data and support documentation would be needed for military applications, spacecraft applications or for repairs done under the supervision of other regulatory agencies.

Topics:

Key Lecture Topics:

  • Overview of composite and adhesive bonding technologies.
  • Strength of composite materials.
  • Original structural material categories: matrix systems, reinforcement fibers, fiber forms, core materials, adhesives, etc.
  • Repair material categories: Prepregs, resins, weaves, cores, potting compounds, adhesives, material substitution options, etc.
  • Material and Process Specification categories applicable to the original laminate and repair design.
  • Repair analysis techniques.
  • Documentation and repair substantiation techniques.
  • Effects of low impact, medium impact, and high impact damage.
  • Co-cured and pre-cured techniques for both wet layup and prepreg repairs.
  • Material properties/allowable data.
  • Strength and Stiffness analysis for both the original and repair laminate.
  • Original and repair laminate testing techniques.
  • Repair scarf joints and bonded doubler repairs.
  • Use and application of the structural repair manual (SRM).
  • Repair documentation and analytical substantiation reports.
  • Repair processing: cure cycles, vacuum bagging, oven curing, autoclave curing, hot bonders and heat blankets, etc.

Workshop Exercises:

  • Hands-on computer analysis of both the original laminate and the repair using simple Excel spreadsheets.
  • Analysis performed on unique repair scenarios as well as on typical structural repair manual (SRM) repairs to determine stiffness margins and strength margins of safety.
  • Repair of damaged composite panel using scarfing techniques, laying up the repair, vacuum bagging and curing the repair to help to give the engineers an appreciation for the subtleties involved in obtaining a high-quality repair.
  • Test coupons are made from both the original laminate and repaired laminates and mechanically tested to determine the strength and stiffness of each.
  • Manufacturing drawings and repair manuals are utilized with the physical repair and combined with the analysis process to experience the real world engineering application of the techniques covered in the course.