Failure analysis of a failed anchor chain link

ARA acknowledges the financial support of Binks Trust through funding made available to the School of Engineering, University of Aberdeen, UK.Peer reviewedPostprin

Compressive Properties of Additively Manufactured Functionally Graded Kagome Lattice Structure

Cellular lattice structures have important applications in aerospace, automobile and defense industries due to their high specific strength, modulus and energy absorption. Additive manufacturing provides the design freedom to fabricate complex cellular structures. This study investigates the compressive properties and deformation behavior of a Ti-6Al-4V unit Kagome structure fabricated by selective laser melting. Further, the mechanical performance of multi-unit and multi-layer Kagome structure of acrylonitrile butadiene styrene (ABS) ABS-M30™ manufactured by fused deposition modeling is explored. The effect of a number of layers of Kagome structure on the compressive properties is investigated. This paper also explores the mechanical properties of functionally graded and uniform density Kagome structure. The stiffness of the structure decreased with the increase in the number of layers whereas no change in peak load was observed. The functionally graded Kagome structure provided 35% more energy absorption than the uniform density structure

Performance of strut-reinforced Kagome truss core structure under compression fabricated by selective laser melting

Lattice structures are regarded as an excellent candidate for lightweight applications owing to their high specific strength and stiffness. In this paper, a novel lattice design is proposed, and its compressive properties are investigated. The Kagome lattice design is modified to form a new lattice core structure, namely, strut reinforced Kagome (SRK) with the presence of extra vertical strut. Ti-6Al-4V SRK unit structures with different aspect ratio are fabricated through selective laser melting. The compressive properties, elastic modulus and peak strength are predicted using analytical solution and are compared with the finite element analysis results and experimental measurements. The SRK unit structures outperformed Kagome unit structures of the same relative density by 13.42% and 12.87% in terms of peak strength and effective modulus, respectively. The sub-β-transus heat treatment on the SRK and Kagome unit structure has led to an increase in the effective moduli, ductility, and energy absorption with a slight decrease in the peak strength.MOE (Min. of Education, S’pore)Published versio

Effect of scarf repair geometry on the impact performance of aerospace composites

This experimental study investigates the effect of scarf geometry in restoring the impact response of scarf-patched 3 mm thick glass-fiber reinforced polymer (GFRP) matrix composite laminates. Traditional circular along with rounded rectangular scarf patch configurations are considered repair patches. Experimental measurements revealed that the temporal variations of force and energy response of the pristine specimen are close to that of circular repaired specimens. The predominant failure modes were witnessed only in the repair patch which includes matrix cracking, fiber fracture, and delamination, and no discontinuity in the adhesive interface was witnessed. When compared with the pristine samples, the top ply damage size of the circular repaired specimens are larger by 9.91%, while that of the rounded rectangular repaired specimens is larger by 434.23%. The results show that circular scarf repair is a more suitable choice of repair approach under the condition of a 37 J low-velocity impact event even though the global force-time response is similar.National Research Foundation (NRF)Published versionThis work was financially supported by the National Research Foundation (NRF) of Singapore under the Corporate Laboratories @ Universities Scheme (ARMS 1.3 project)

Three-dimensional topography modelling of regular prismatic grain coated abrasive discs

Regular precision-shaped abrasive grains are preferred to irregular grits due to their superior performance regarding uniform polishing. Three-dimensional modelling of abrasive disc’s topography is essential to understand the material removal rate and surface roughness estimations through finite element based numerical simulations. Topography modelling of one such precision (prism)-shaped grain abrasive disc is carried out in this work through stochastic studies. The abrasive discs are scanned using laser profilometer, and high-frequency noise is filtered out using spectral analysis. Spatial parameters such as autocorrelation length and texture aspect ratio are considered for the topology mapping. Based on the statistical information from the measured grit sizes #60 and #120, such as peak protrusion grain height, spatial distributions, the topography is simulated. The analysis reveals that the peak height and spatial distribution follow a normal distribution. Unlike irregularly shaped grains where the orientations of the grains are neglected, the height variations in the precision-shaped grains in coated abrasive discs are mainly caused by random orientations of the grains. So, iterations are carried out for orientation in the three (mutually perpendicular) axes of the grain till the required statistical parameters are achieved. Surface fitting is performed for the distributed grains and the 3D-surface parameters of the simulated coated abrasive topography match well with the actual discs.ASTAR (Agency for Sci., Tech. and Research, S’pore

Enhanced cooling rates in laser directed energy deposition with interlayer peening

Purpose: This study aims to investigate the effect of mechanical peening on the cooling rate of a subsequently deposited layer in a hybrid additive manufacturing (AM) process. Design/methodology/approach: In this experimental study, 20 layers of 316 L stainless steel are built via directed energy deposition, with the tenth layer being subject to various peening processes (shot peening, hammer peening and laser shock peening). The microstructure of the eleventh layer of all the samples is then characterized to estimate the cooling rate. Findings: The measurements indicate that the application of interlayer peening causes a reduction in primary cellular arm spacing and an increase in micro segregation as compared to a sample prepared without interlayer peening. Both factors indicate an increase in the cooling rate brought about by the interlayer peening. Practical implications: This work provides insight into process design for hybrid AM processes as cooling rates are known to influence mechanical properties in laser-based AM. Originality/value: To the best of the authors’ knowledge, this work is the first of its kind to evaluate the effects of interlayer peening on a subsequently deposited layer in a hybrid AM process.Agency for Science, Technology and Research (A*STAR)Nanyang Technological UniversitySubmitted/Accepted versionThe funding support from Advanced Remanufacturing Technology Centre (ARTC), Singapore and Nanyang Technological University is gratefully acknowledged. Abeer acknowledges the financial support from A*STAR Graduate Academy (AGA), Singapore in the form of a PhD scholarship

Printing and characterisation of Kagome lattice structures by fused deposition modelling

Sandwich structures with lattice cores exhibit high specific bending strength and stiffness when compared to monolithic structures. Additive manufacturing is able to further expand the available design space to fabricate novel core structures with complex features. In this paper, the compressive performance of the Kagome truss unit cell of acrylonitrile butadiene styrene (ABS) ABSplus™ fabricated by fused deposition modelling is investigated. The influences of part build orientation, truss radius and surface roughness on strength and stiffness are critically explored. The change in build orientation improved the average peak strength and effective stiffness by 23% and 19%, respectively. 90% (v/v) acetone was used to polish the printed surfaces and 5 min chemical treatment was optimal based on the measured surface roughness, strength and stiffness values. These single cell studies will help to understand the macroscopic behaviour of the beams and plates with Kagome cores under quasi-static bending and impact loading scenarios.MOE (Min. of Education, S’pore

Processing and characterisation of MWCNT reinforced aluminum matrix composites

Metal matrix composites comprising aluminum matrix and multi-wall carbon nanotubes (MWCNTs) as reinforcements are fabricated using cold uniaxial compaction followed by sintering and cold extrusion as secondary processes. The MWCNTs are pretreated with sodium dodecyl sulfate (SDS) for improved adhesion with aluminum powder. The effect of sintering temperature on the microstructure is explored using differential scanning calorimetric (DSC) spectrum. The tensile yield and ultimate strength of Al/MWCNTs increased to 90% with 2 wt% addition of MWCNTs. Various theories for the strengthening and stiffening of Al/MWCNTs composites are explored.Accepted versio

Thermo-mechanical debonding map for repairing composite–metal adhesive joints

Adhesive bonding is one of the dominant joining technologies in Design for Assembly to obtain innovative engineering products with complex geometries. These permanently bonded joints could be disassembled for repair purposes using the thermo-mechanical debonding technique to salvage the high-cost composite components without any damage. In this work, the temperature dependent storage modulus, loss modulus and tensile properties of the bulk modified epoxy film adhesive were measured through instrumented tests. Glass fibre reinforced composite and Ti–6Al–4V alloy sheets were bonded with the modified epoxy film adhesive and the floating roller peel performance was studied as a function of temperature to understand the load-displacement and failure mechanisms for generating a debonding map. The debonding region was identified in the temperature range between 1.17 Tg and 1.33 Tg. The knock-down in storage modulus and initial peel load exhibited a similar trend with respect to the temperature.Agency for Science, Technology and Research (A*STAR)Economic Development Board (EDB)Nanyang Technological UniversityNational Research Foundation (NRF)Accepted versionThis work was conducted within the Rolls-Royce@NTU Corporate Lab under the project ‘ARMS 1.3 Repair of Composite Aero-engine Structures’ with support from the Industry Alignment Fund (IAF) Singapore under the Corp Lab@University Scheme

Failure Mode Analysis Of Kagome Lattice Structures

Ultralight weight structures are today’s essential need in aerospace, marine and automotive industries. Strength and stiffness optimization of load bearing structures is made possible with the evolution of additive manufacturing technologies through shape or topology optimization. Further composite materials and sandwich constructions reduce the design weight. To fully realize the lightweight structure, core designs with low density and high strength are necessary for sandwich panel design. In this study, the performance of the 3D Kagome truss core structure in compression loading is experimentally investigated. These bio-inspired core structures are fabricated by Fused Deposition Modelling (FDM) with Acrylonitrile butadiene styrene (ABS) ABSplus® material for experimental validation purposes. The geometrical parameters of the Kagome structure in terms of its slenderness ratio are varied to study the switch of failure mechanism from yielding dominant behavior to buckling. The effective stiffness of the truss found from finite element modeling and based on experimental results are compared, and the reasons for their discrepancy are explored. The modulus of the Kagome unit-cell is found to be linearly related to its relative density. The result show that with the increase in the slenderness ratio (l/r), the strength of the Kagome structure decreases.MOE (Min. of Education, S’pore)Published versio