Mechanical properties and tribological behaviour of electroless Ni–P–Cu coatings on corrosion-resistant alloys under ultrahigh contact stress with sprayed nanoparticles.

Threaded components manufactured from corrosion resistant alloys (CRA's) are vulnerable to galling. This paper develops a test matrix to systematically investigate the mechanical properties and tribological performance of electroless nickel phosphorous coatings on CRA's when subjected to high contact stress. Samples manufactured from 28Cr stainless steel were shot-peened for various periods prior to being electo/electroless coated. The coefficient of friction (CoF) of different coating systems was evaluated via sliding cross-pin method. Various wet and dry lubricants were utilised to examine tribological performance, furthermore the adhesion strength of the coatings was investigated by a bond and pull-off method. The study has shown a significant reduction in CoF for electroless nickel phosphorous coatings with prior shot-peening treatment and sprayed nanoparticles.N/

Effects of marine environment exposure on the static and fatigue mechanical properties of carbon fibre-epoxy composite

This thesis studies the static and fatigue failure of carbon fibre-epoxy composite for marine use. The primary objective is to investigate the effects of sea water ingress on the static and cyclic performance of laminated composites, by using the combination of experimental, numerical and analytical approaches. Experiments were carried out to collect evidence, including data and images, for further analysis. Samples were made from autoclave-cured carbon fibre-epoxy pre-preg for the static, moisture diffusion and fatigue tests. Three chambers were used in the diffusion test, containing fresh water (tap water), sea water and sea water at 70 bar hydrostatic pressure respectively. And the chambers were placed in an oven at a constant temperature 50 °C in order to accelerate the water absorption. Optical and scanning electron microscopies (SEM) were employed to inspect for manufacturing defects and to identify the failure modes. Some formulae were derived to predict the material properties of laminated composites, to validate the mechanical tests, and to explain the failure criteria of composites. Finite element analysis (FEA) was employed to study the phenomena that were observed in the experiments. FEA has the aim to simulate the static, diffusion and fatigue behaviour involving multiphysics and multiscale effects. The FEA modelling has revealed details of the stress and moisture distributions, which have helped to understand the failure mechanisms of laminated composites. Classical laminate theory (CLT) was employed to develop an analytical model. The basic principles of CLT were extended to three-dimensions, and the analytical solution was critically compared with the FEA results. Some MATLAB tools based on CLT were developed to predict the properties of laminated composites and to analyse the experimental data. These MATLAB codes are shown in the appendix. This thesis has contributed to an improved knowledge of the failure mechanisms of composite materials in both normal and marine environments, and to optimize structural design of FRP composites.School of Marine Science and Engineering, Plymouth Universit

Multi-scale modelling of moisture diffusion coupled with stress distribution in CFRP laminated composites

Laminated composite structures operating in a marine environment are subject to moisture ingress. Due to the slow diffusion process of moisture, the distribution of moisture is not uniform so that the laminates can develop hygrothermal stresses. An accurate prediction of the moisture concentration and the associated hygrothermal stress is vital to the understanding of the effect of marine environment on failure initiation. The present paper investigates the time-dependent moisture diffusion and the stress distribution in carbon fibre reinforced polymeric (CFRP) composites by means of experimental study and Finite Element Analysis (FEA). Samples were made from CFRP pre-preg autoclave-cured, and then immersed in fresh water and sea water at a constant 50 °C for accelerated moisture diffusion. Laminates with [0]16, [90]16, [±45]4s lay-up sequences were investigated. A multiscale 3D FEA model was developed to evaluate the interfacial stresses between polymer matrix and carbon fibre and the stress distribution in the composite laminates. The analysis revealed that both the stress distribution and stress level are time-dependent due to moisture diffusion, and the interphase between fibres and matrix plays an important role in both the process of moisture diffusion and the stress/strain transfer. The interlaminar shear stresses of the laminates induced by hygrothermal expansion exhibited a significant specimen edge effect. This is correlated with the experimental observations of the flexural failure of laminates

Effects of hygrothermal stress on the failure of CFRP composites

This paper investigates the hygrothermal effects on the failure mechanisms in bending of carbon fibre reinforced polymer (CFRP) composites. Accelerated diffusion testing was carried out by immersion at 50 °C constant temperature and 70 bar hydrostatic pressure to study the effects of fresh or sea water diffusion into pre-preg CFRP laminates. Consequently the composite laminates were tested in bending after 1 and 3 months’ immersion. A three-dimensional finite element analysis (FEA) model was developed to couple the moisture diffusion, hygrothermal expansion and bending. Optical and field emission scanning electronic microscope (SEM) were employed to analyse the failure mechanisms of CFRP composites in bending after immersion. The study showed that the mechanical properties are significantly reduced after short term immersion due to the edge effects, while the damage to the fibre/polymer interface becomes more significant to laminate degradation after longer-term immersion

The effects of unequal compressive/tensile moduli of composites

Abstract This paper investigates the effects of unequal compressive and tensile moduli of carbon fibre reinforced plastic (CFRP) composites. The basic assumption is based on the statistics that the compressive modulus is a fraction lower than the tensile modulus. Data evaluated by Finite Element Analysis (FEA) model, Classical Laminate Theory (CLT) model, and experiment are used to investigate these effects. The terms of compressive modulus are successfully introduced into the Tsai–Wu failure criterion for the production of failure envelops, into the Classical Beam Theory (CBT) and CLT for the investigation of flexural behaviour as well as the fibre microbuckling model for the analysis of compressive failure. The study shows that the failure criteria shift from stress domain to strain domain when the compressive modulus is considered, and the strain dominated failure criteria could generally provide more accurate prediction in composite material. Therefore it is proposed to apply strain dominated failure criteria for composite design, testing and certificate.Abstract This paper investigates the effects of unequal compressive and tensile moduli of carbon fibre reinforced plastic (CFRP) composites. The basic assumption is based on the statistics that the compressive modulus is a fraction lower than the tensile modulus. Data evaluated by Finite Element Analysis (FEA) model, Classical Laminate Theory (CLT) model, and experiment are used to investigate these effects. The terms of compressive modulus are successfully introduced into the Tsai–Wu failure criterion for the production of failure envelops, into the Classical Beam Theory (CBT) and CLT for the investigation of flexural behaviour as well as the fibre microbuckling model for the analysis of compressive failure. The study shows that the failure criteria shift from stress domain to strain domain when the compressive modulus is considered, and the strain dominated failure criteria could generally provide more accurate prediction in composite material. Therefore it is proposed to apply strain dominated failure criteria for composite design, testing and certificate

Marine environmental effects on a graphene reinforced epoxy adhered single lap joint between metals and CFRP

This study investigates the marine environmental effects on the bonding strength of graphene nanoplatelets (GNPs) reinforced adhesive for a metal/composite single lap joint. Samples were immersed for periods of 1, 2 and 3 weeks in a 50 °C, 3.5% NaCl solution, with the purpose of the heat being the creation of an environment in which simulated an increased ageing period in the joint structure. In a dry condition, the use of GNPs produced a slight increase in lap shear strength of 17% and 14% in the carbon fibre reinforced plastics (CFRP) composite laminate to aluminium and stainless-steel joints respectively. Post immersion, the stainless-steel samples endured 10% less strength degradation than the aluminium samples in the cases with and without GNPs, however the degradation between the same materials with and without GNPs differed less than 2%. On the other hand, the rate at which the materials with GNPs and without GNPs degraded, differed greatly between immersion periods. Mathematical methods were carried out via analytical calculation and FEA modelling, for which values converged with experimental results. The outcomes of these experiments have been the production of highly useful information in terms of material selection and adhesive modification via GNPs for use in the marine environment