Transverse tensile strength of unidirectional fibre-reinforced polymers and self-healing of interfacial debonding

Abstract

A study of the healing of interfacial debonding in fibre-reinforced polymers (FRPs) was performed. In the composite, a microencapsulated healing agent and a solid chemical catalyst are dispersed within the coating layer on the surface of the fibres. Healing is triggered by crack propagation through the microcapsules, which then release the healing agent into the crack plane. Subsequent exposure of the healing agent to the chemical catalyst initiates polymerisation and bonding of the crack faces. Self-healing is demonstrated on flat tensile specimens of neat epoxy (no fibres) and unidirectional FRPs. The ratio of tensile strengths of the virgin and healed materials is used to quantitatively measure crack healing.     

The Effect of Resin Matrix Composition on Mechanical Properties of E-glass Fiber-Reinforced Composite for Dental Use

The effects of resin matrix composition including bis-phenol-A-diglycidyl dimethacrylate (bis-GMA)-methyl methacrylate (MMA) based or urethane dimethacrylate (UEDMA)-triethylene glycol dimethacrylate (TEGDMA) based composition and storage conditions on the mechanical properties of E-glass fiber-reinforced composites (FRCs) were studied. Three experimental groups ('Exper 1', 'Exper 2', 'Exper 3') with differing UEDMA to TEGDMA ratio in the matrix together with a control group ('Control') based on bis-GMA–MMA resin matrix were prepared by light-curing. The storage conditions for each group were dry storage at room temperature for 24 h and 30- and 60-day immersion in deionized (DI) water at 37°C, which further divided each group into three subgroups. For all the four composition groups, mechanical properties including hardness, flexural strength and modulus in both three-point and four-point bendings were tested (n = 6), together with water sorption and solubility study (n = 6) and fracture site scanning with a scanning electron microscope (SEM). The experimental specimens were relatively strong and stiff in three-point bending compared to previous research. The same specimens in three-point bending had a lower flexural modulus and fractured at higher flexural stress than in four-point bending. According to the SEM images after fracture, some resin matrix was still bound to the fiber surface, showing cohesive–interfacial fracture type and relatively stable matrix–fiber adhesion. According to comprehensive analysis, the control group showed superior mechanical performance in most of the tests.     

Technical note Fabrication of alumina dispersion strengthened copper strips by internal oxidation and hot roll bonding

Abstract

Alumina dispersion strengthened copper strips were fabricated by internal oxidation and hot roll bonding of Cu–Al alloy strips. Cu–Al alloy strips were internally oxidised without using any oxidant powders by a surface oxidation method. Several of the internally oxidised alloy strips were stacked and bonded by rolling at high temperatures. The bonded strip was cold rolled to achieve tensile strengths of 484–539 MPa and yield strengths of 472–522 MPa with thermally stable mechanical properties.     

31—OBSERVATIONS ON THE MECHANICAL BEHAVIOUR OF LINCOLN-WOOL FIBRES SUPERCONTRACTED IN LITHIUM BROMIDE SOLUTION

A brief summary of certain phenomena associated with the two stages of supercontraction in aqueous lithium bromide solution is given; in particular, the mechanical properties, in the cold solution, of wool fibres at the end of each stage are discussed. Results previously obtained by Feughelman and Haly are reinterpreted in terms of the simple two-phase model of crystalline microfibril embedded in a less ordered matrix. On the basis of certain assumptions, it is possible to obtain an estimate of the Stress–Strain curve of the matrix in LiBr solution. The matrix Stress–Strain curve so obtained compares well with the theoretical inverse Langevin rubber-elasticity curve up to a certain strain level.

A value for the number of random links between cross-links is obtained.     

Influence of P on hot ductility of high C,Al, and Nb containing steels

Abstract

Hot ductility curves for high carbon Nb and Nb free steels have been determined immediately after casting at two P levels, ~0.01% and ~0.045%. High strain rates of 0.1-0.55 s^-1 were generally used but some limited low strain rate testing at 7 × 10^-3 s ^-1 was carried out on Nb containing steels. Nb containing steels showed, as expected, worse ductility than the Nb free steel but high P level was detrimental to ductility for both steels and ductility in general was very poor. Failure was intergranular with the presence of films of a P rich phase at the boundaries in the case of the Nb free steels and in addition to this, in Nb containing steel there was a Nb rich phase. The films were thicker and more continuous in the higher P steels. It is suggested that the P rich films are probably the low melting point phase Fe₃P or Fe₃(Mn)P, which can remain liquid down to temperatures as low as 950°C. Some back diffusion of P into the grain interior is possible if the strain rate is reduced and/or at high testing temperatures during the 5 min hold prior to testing. This allowed some improvement in ductility to occur in the lower P containing steels by reducing the amount of the low melting point phase at the boundaries.     

Martensitic transformation kinetics and shape memory effect in Co–Ni alloys

Abstract

The shape memory effect (SME) and martensitic transformation kinetics in Co–Ni alloys were studied. The degree of SME decreased with increasing Ni content, and was proportional to the pre-existing ? martensite content, suggesting that the SME in Co–Ni alloys is related to the coalescence of the pre-existing ? plates. Thermal cycling (α ?) increased the ? martensite content, and the SME became greater with an increasing number of thermal cycles. The martensitic transformation kinetics of Co–Ni alloys can be expressed as Y = 1- exp[-0.00526(M _s-25)], where Y is the volume fraction of ? martensite and M _s is the starting temperature of martensitic transformation (°C).     

Study of structure/property relationships of diffusion bonded Ti6Al4V + 10 wt-%TiC particulate composite

Abstract

Ti–C particulate reinforced Ti6Al4V metal matrix composites (Ti6Al4V + 10 wt-%TiC) have demonstrated a high strength-to-weight ratio as well as good high temperature properties. A poor fusion welding performance is commonly observed in these materials making solid-state diffusion bonding a potential process to produce complex structural components. This work aims to characterise the microstructure and the mechanical properties of Ti6Al4V + 10 wt-%TiC diffusion bonded joints. Microstructural evaluation has been performed using both optical and scanning electron microscopy. Mechanical characterisation consisted of room temperature microflat tensile tests for the different bonding conditions and microhardness along the joint. The best results were associated with a bonding temperature of 1000°C and pressure 5 MPa together with bonding times ranging from 35 to 60 min.     

Centrifugal casting of functionally graded aluminium matrix composite components

Abstract

Centrifugal casting is one of the potential manufacturing techniques used for producing near net shaped components with improved properties. The emergence of new class of functionally graded materials has made it an important technique for the fabrication of engineering components and structures with graded property. The present paper describes the studies carried out on processing and characterisation of functionally graded Al matrix composites components based on Al–SiC ex situ and Al–Si in situ composites. The microstructural and mechanical characteristics of the composites are evaluated. In the case of Al–SiC functionally graded metal matrix composites discs, the particles are segregated gradiently towards the outer periphery of the casting exhibiting high strength and hardness towards the outer periphery. The Al–Si in situ composite cylinder shows the dispersion of primary Si particles towards the inner periphery of the casting which can lead to higher hardness and wear resistance.     

Influence of intercritical austenitising,tempering time and martensite volume fraction on the tensile properties of ferritic ductile iron with dual matrix structure

Abstract

The present study investigates the effects of intercritical austenitising, tempering time and martensite volume fraction on the tensile properties of ferritic ductile iron with a dual matrix structure. The results showed that a structure having proeutectoid ferrite plus martensite (the dual matrix structure) has been developed and that the volume fraction of proeutectoid ferrite and martensite can be controlled to influence the strength and ductility. Specimens quenched from the (α+γ) temperature range exhibited significantly greater ductility than conventionally heat treated specimens. By changing only the intercritical austenitising time and keeping the rest of the heat treatment conditions constant it was observed that specimens intercritically austenitised for 30 s exhibited higher strength and ductility than those intercritically austenitised for 20 min. This was considered to result from carbon enrichment of the austenite depending on the time for carbon diffusion during intercritical austenitising. The specimens intercritically austenitised for 30 s and having ～49% martensite volume fraction exhibited the best combination of high strength and ductility. The tensile and proof stresses of this material are much higher than pearlitic and ferritic grades and ductility is significantly lower than ferritic grades.     

Microstructure and tensile properties of Ni3 (Si,Ti) alloys containing second phase dispersions

Abstract

The alloying behaviour, microstructure, and high temperature mechanical properties of quaternary polycrystalline Ni₃ (Si,Ti), which was alloyed with transition elements V, Nb, Zr, and Hf beyond their maximum solubility limits, were investigated. The solubility limits of the quaternary elements in the L1₂ Ni₃ (Si,Ti) phase were determined to be ranked in the sequence of Nb > V > Hf > Zr, and correlated with the size misfit parameter between Si and the quaternary element X, and with the difference in formation enthalpy between Ni₃ Si and Ni₃ X. The second phases (dispersions) formed beyond the solubility limit were identified as a face centred cubic type Ni solid solution for the V containing Ni₃ (Si,Ti) alloy and Ni₃ X type compounds of the Nb, Zr, and Hf containing Ni₃ (Si,Ti) alloys. The second phase dispersions in the L1₂ phase matrix resulted in strengthening over a wide range of temperatures. The high temperature tensile elongation was improved by the introduction of the second phase dispersions. Among the quaternary Ni₃ (Si,Ti) alloys observed in the present study, the Nb containing Ni₃ (Si,Ti) alloy with the Nb containing second phase dispersion was shown to have the most favourable mechanical properties.