Finite element analysis and experimental validation of polymer-metal contacts in block-on-ring configuration

The wear profile analysis,obtained by different tribometers,is essential to characterise the wear mechanisms.However,most of the available methods did not take the stress distribution over the wear profile in consideration,which causes inaccurate analysis.In this study,the wear profile of polymer–metal contact,obtained by block-on-ring configuration under dry sliding conditions,was analysed using finite element modelling(FEM)and experimental investigation.Archard’s wear equation was integrated into a developed FORTRAN-UMESHMOTION code linked with Abaqus software.A varying wear coefficient(k)values covering both running-in and steady state regions,and a range of applied loads involving both mild and severe wear regions were measured and implemented in the FEM.The FEM was in good agreement with the experiments.The model reproduced the stress distribution profiles under variable testing conditions,while their values were affected by the sliding direction and maximum wear depth(hmax).The largest area of the wear profile,exposed to the average contact stresses,is defined as the normal zone.Whereas the critical zones were characterized by high stress concentrations reaching up to 10 times of that at the normal zone.The wear profile was mapped to identify the critical zone where the stress concentration is the key point in this definition.The surface features were examined in different regions using scanning electron microscope(SEM).Ultimately,SEM analysis showed severer damage features in the critical zone than that in the normal zone as proven by FEM.However,the literature data presented and considered the wear features the same at any point of the wear profile.In this study,the normal zone was determined at a stress value of about 0.5 MPa,whereas the critical zone was at about 5.5 MPa.The wear behaviour of these two zones showed totally different features from one another.

Engineering phosphorus-containing lignin for epoxy biocomposites with enhanced thermal stability,fire retardancy and mechanical properties

Fabricating a high-performing thermoset using bio-based flame retardant is critical for the sustain-able development of engineering materials with superior fire safety and robust mechanical properties.Herein,the epoxy(EP)composites with the industrial requirements are manufactured with a novel high-efficient,lignin-based flame retardant named DAL-x,which is fabricated by grafting 9,10-dihydro-9-oxa-10-phosphaze-10-oxide(DOPO)onto lignin.The resulting DAL-x/EP composite exhibits excellent flame retardancy with a desirable UL-94 V-0 rating and a satisfactory limiting oxygen index(LOI)of 29.8%due to the appropriate phosphorus content of DAL-x with adjustable molecular chain structure.More-over,the DAL-x/EP composite shows an unexpected improvement in the elastic modulus(∼36%)and well-preserved strength and ductility compared with those of pure EP.This work offers a feasible strat-egy for creating efficient bio-based flame retardants utilizing industrial waste lignin and preparing high-performance EP composites that meet the demanding requirement of fire retardancy in industries,con-tributing to the circular economy and sustainability.

Influence of graphene nanoplatelets on mechanical properties and adhesive wear performance of epoxy-based composites

Epoxy resin is one of the most widely used thermoset polymers in high-performance composite materials for lightweight applications.However,epoxy has a high coefficient of friction,which limits its tribological applications.In this study,the effect was investigated of different weight fractions of solid lubricant graphene nanoplatelets(GNPs),ranging from 0 to 4.5 wt%,on mechanical and adhesive wear performance of epoxy.Adhesive wear tests covered mild and severe wear regimes.The correlation of tribological and mechanical properties was studied as well.Scanning electron microscopy(SEM)was used to observe the failure mechanisms for both tribological and mechanical samples after each test.The results revealed that the addition of GNPs to the epoxy improved its stiffness and hardness but reduced its fracture strength and toughness.Adhesive wear performance exhibited high efficiency with GNP additions and showed reductions in the specific wear rate,the coefficient of friction,and the induced interface temperature by 76%,37%,and 22%,respectively.A fatigue wear mechanism was predominant as the applied load increased.Most importantly,severe wear signs occurred when the interface temperature reached the heat distortion temperature of the epoxy.The tribological,and mechanical properties showed only a weak correlation to each other.The addition of GNPs to epoxy by less than 4.5 wt%was highly efficient to improve the wear performance while maintaining the fracture strength and toughness.Fourier transform infrared spectroscopy(FTIR)analysis shows no chemical interaction between the epoxy matrix with GNPs,which implies its physical interaction.