Manufacturers of aerospace propulsion systems are well aware of the positive effects of compressive residual stress (RS) fields on turbo-machinery components in terms of improved fatigue life and durability. Tensile RS, however, can cause unfavorable conditions which may lead to premature failure during operational usage. Thus, the industry objective is to capitalize on compressive RS and prevent or minimize tensile RS at critical locations of engine components but this requires a new NDE/I capability. The Proto Team intends to exploit high energy x-ray diffraction (HEXRD) technologies and demonstrate feasibility for measuring RS distributions non-destructively at subsurface depths in a high-strength aerospace material. Initial experimentation will be performed on laser-peened titanium as the basis for establishing feasibility. The related challenge in this effort is to define and design a small transportable system that can be installed in a factory or depot setting while retaining the depth and resolution performance of the much larger research systems. The Proto Team will capitalize on the experimental research of Iowa State University into HEXRD for measuring subsurface RS and Protos expertise in developing, fielding and delivering low-energy, highly portable XRD systems. The Metal Improvement Company will provide Ti-alloy LSP specimens and modelling support.
Benefit: Proto will develop a non-destructive inspection system utilizing high-energy x-ray diffraction (HEXRD) technologies for nondestructively and quantitatively measuring subsurface residual stress (RS) profiles in aerospace turbine engines. While Protos current man-portable systems provide a sound basis for in-situ diagnostics of surface RS, the new transportable NDE/I system will provide a dramatic advancement enabling a fuller evaluation of the state of RS and a definitive contribution to the structural health of propulsion components. Current low-energy XRD technology samples metals to a depth of roughly 10 to 20 microns depending on the metal, but Proto proposes to use higher energy x-rays and extend interrogation much deeper to 2 to 3 mm or more. This advancement will yield subsurface RS profiles nondestructively. Protos HEXRD system will support in-house research and robust quality assurance and life prediction programs for metal engine components. The technical basis and feasibility of this enhanced system will be demonstrated on laser-peened titanium in Phase I. The more mature system that is to be demonstrated in Phase II will provide OEMs, military researchers and DOD depots a transportable capability to non-destructively measure the subsurface RS state of engine components. It will provide a sound method for: (1) Process control, testing and verification of RS; (2) Managing product quality and weight reductions; and (3) Supporting materiel disposition and life prediction decisions based on actual RS fields. Fundamentally, Protos HEXRD system will form the basis for RS life-cycle management of engine componentsa new paradigm.
Keywords: Nondestructive Testing, Nondestructive Testing, NDE/I, Residual Stress, XRD, high energy x-ray diffraction, residual stress depth profiling, subsurface residual stress
