Domenico Furfari

Compression After Multiple Impacts: Modelling and Experimental Validation on Composite Curved Stiffened Panels

This research investigates the post-impact behaviour of composite fuselage panels subjected to multi-site low-velocity impacts. Large curved stiffened panels (1.2 m × 0.8 m, with composite skins/stiffeners and aluminium frames) of two different skin thicknesses were subjected to sequential drop-weight impacts at locations previously determined to be critical in FE simulations. After assessment of the impact damage, each panel was tested in compression. High-speed video, strain gauges, digital image correlation and acoustic emission were used to monitor the failure development and to provide data for comparison with the FE simulations. The FE models, which were based on a mesomechanical approach, showed a good agreement with both the impact damage and the subsequent compression performance.

Finite Element Analysis for Advanced Repair Solutions: A Stress Analysis Study of Fastened and Bonded Fuselage Skin Repairs

The advanced repair solutions investigated within this research programme, both mechanically fastened and adhesively bonded repairs, could extend their in-service life beyond the Design Service Goal (DSG) of the aircraft in which they are embodied. Beside the test activity (discussed in previous publications), calculation methods (based on Finite Element models) were developed to improve current methods to predict the fatigue behavior of repairs and to optimize the design principles of the advanced repair solutions. The use of internal doubler to reduce the secondary bending, different fastener type or additional fastener row, as well as, the influence of fastener installation (Hi-Lok® interference fit) are reported. Other advanced repair solutions, such as bonded repair or the use of glare® doubler to repair aluminum skin, were also investigated and reported in this work. In this paper different kind of Finite Element (FE) models used to simulate the tests are reported. The stresses resulted from the FE analysis were compared with the ones measured experimentally by strain gauges.

Laser Shock Peening to Repair, Design and Manufacture Current and Future Aircraft Structures by Residual Stress Engineering

This paper will provide an overview on potential applications for the aerospace industry for repairing aircraft as well as to ensure salvage for identified hot spots in terms of fatigue and crack growth performance. Residual stress engineering is a field of engineering aiming to improve the economic and ecological impact of future aircraft structures by controlling the residual stresses induced by Laser Shock Peening (LSP). Managing the residual stresses for designing structures represents an innovative approach for next generation aircraft. Predicting crack turning induced via a LSP treatment and the optimization of the LSP treatment itself for reaching the crack growth design stress for the targeted weight benefit will be discussed. Advanced forming processes in aircraft manufacturing represent another potential area of interest and the benefits and challenges of applying laser peen forming in this context will be presented. The aeronautical industry requirements for future developments of the laser shock process will also be included for applications ranging from the repair environment to design and manufacturing of aircraft structures.

Experimental investigation of reinforced bonded joints for composite laminates

An experimental study has been carried out to investigate the behaviour of co-bonded carbon fibre reinforced plastics joints with a novel design incorporating a through the thickness local reinforcement. Different specimens were manufactured to investigate static and fatigue behaviour, as well as delamination size after impact and damage tolerance characteristics. The mechanical performances of the specimens with local reinforcement, consisting of the insertion of spiked thin metal sheets between co-bonded laminates, were compared with those ones obtained from specimens with purely co-bonded joints. This novel design demonstrated by tests that damage progression under cycling load results significantly delayed by the reinforcements. A significant number of experimental results were obtained that can be used to define preliminary design guidelines.

Compression After Multiple Impacts: Modelling and Experimental Validation on Composite Coupon Specimens

This research investigates the post-impact behaviour of CFRP coupon specimens subjected to multisite impacts. Sequential low-velocity impacts at different locations were performed on coupons with different thicknesses. The impact load history was recorded, and the extent of damage was assessed by ultrasonic inspection. The residual strength in compression was then measured in a compression after impact rig which was specially modified for the testing of thin composites. High-speed video and digital image correlation records were taken for a number of specimens during testing. The experimental results were used to validate a finite element mesomechanical modelling approach which accounts for both intralaminar damage and interlaminar damage.