Other Technology Days have focussed on durability, reliability and associated data analytics of in-field, proving ground and laboratory vehicle testing (hosted in 2020) and applications of measurement, monitoring and modelling for electrical, acoustical and structural performance from batteries to bridges to aircraft landing gear and electric vehicles (2022 edition). Both the presentation recordings and downloadable content is available to access below.
A wide range of joints is used to assemble structures including welds, rivets, bolts, and adhesives, between similar and dis-similar materials - metals, polymers and composites. These joints distribute load into or through the structure, and when these loads vary during operational use they introduce fatigue cycling at and close to the joint. The local geometry detail at the joint acts as a stress raiser reducing the fatigue strength at the joint. Any evaluation of the durability of the structure must therefore place a high priority on a fatigue assessment of the joints.
This seminar presents an overview of fatigue simulation methods to predict the fatigue performance of joints and focuses on the stress severity factor method commonly used to give an indication of which locations are fatigue critical in an aircraft structural joint.
Welding is a commonly used and effective method for making structural joints between metal parts. However, the nature of the welding process means that these welds generally have a fatigue strength that is inferior to that of the parts being joined together. The result is that, even in a well-designed structure, the welded joints are likely to fatigue. Any evaluation of the durability of a welded structure must therefore place a high priority on a fatigue assessment of the welded joints.
This presents applications and methods for the fatigue life prediction of welds from finite element results. These include mesh insensitive structural stress techniques for both shell and solid elements making model generation less time-consuming. This concludes by describing the material testing and subsequent fatigue characterization required to obtain the bending and membrane weld fatigue curves for seam weld and spot weld damage models.
Cranfield University is leading a five-year research programme with multiple UK universities for New Wire Additive Manufacturing “NEWAM”. This is a directed energy deposition additive manufacturing technology, with a research focus on process, material and structural integrity. Linear “walls” of material are manufactured for cutting and machining into test specimens for non-destructive and destructive tests.
Coventry University is leading the “Material Performance and Structural Integrity” of NEWAM, determining structural integrity through fatigue initiation, fatigue fracture, and residual stress. Prenscia is contributing mechanical fatigue testing services and material characterization services to this NEWAM research programme.
Aircraft landing gear manufacturing and overhaul/maintenance processes alter surface material properties that influence fatigue life. As aging aircraft continue to be pushed beyond their originally intended service life, it has become increasingly critical to characterize specific surface processing conditions. For this reason, Select Engineering Services, General Atomics and Prenscia are conducting research/testing to develop tools and methods that incorporate surface treatment effects in USAF landing gear fatigue models.
Laser shock peening is an emerging technology used for the enhancement of the fatigue performance of safety-critical components and structures. This is achieved through the introduction of a beneficial compressive residual stress field in the near-surface layer of the component which counteracts applied tensile stresses and so extends the fatigue life. In the aerospace industry laser, shock peening has been applied to the root of engine turbine blades and wing attachment lugs.
All of the previous seminar sessions in this HBK Technology Days virtual seminar series have described or used results from fatigue tests performed by the Prenscia Advanced Materials Characterisation & Testing (AMCT) facility. This seminar presents these facilities and fatigue testing capabilities of the AMCT, and subsequent characterisation into strain-life, stress-life and/or load-life fatigue curves.
The AMCT specialises in strain-controlled fatigue testing in the low cycle fatigue (LCF) and high cycle fatigue (HCF) regions, typically between 500 and 5,000,000 cycles. Above this, very high cycle fatigue (VHCF) testing introduces additional challenges.
Like their thermal-engine counterparts, electric vehicles are susceptible to structural fatigue failures. The mechanical complexity of the battery structure and its mountings also give rise to significant additional fatigue failure issues. Insights into these structural and vibration-induced failures enable engineers to eliminate the risk of fatigue failure, improve the durability of battery structures, and increase vehicle reliability.
This seminar considers fatigue design of battery packs, accelerated vibration testing of battery packs and fatigue analysis of electric vehicle structures with industry applications.