This paper describes a microstructure-based uniaxial strain-controlled fatigue life prediction model applied to A319 aluminum alloy which is widely used in automobile industry. The materials made with different casting conditions are characterized and quantified in terms of secondary dendrite arm spacing (SDAS), size, and aspect ratio of eutectic Si particles. Uniaxial low cycle fatigue tests have been performed on four groups of A319 alloy under different casting conditions in which cooling rate and Sr addition are variables. It is shown that the effect of various degrees of microstructure on the fatigue life and fatigue behavior is obvious. The first part of the paper is quantitatively characterizing the microstructure of samples to identify the influence of different casting conditions. With regard to mechanic properties, the tensile properties and fatigue behavior of samples are analyzed combining with microstructure. Finally, a microstructure-based Manson-Coffin-Basquin model is proposed to predict fatigue life of Al-Si alloy.
Purpose
The purpose of this paper is to understand the effect of particle content, applied load and sliding speed on the tribological properties of A356-SiCP composites manufactured using a newly developed vacuum stir casting technique.
Design/methodology/approach
A356 alloy reinforced with 10, 15 and 20 vol% SiC particles was prepared by vacuum stir casting. Tribological tests were carried out on block-on-ring tribometer under dry sliding conditions, room temperature. Wear mechanism was investigated by scanning electron microscope and energy dispersion spectrum.
Findings
SiCP is homogeneously dispersed in the matrix. The increase in SiCP content decrease wear rate, but it leads to an increase in coefficient of friction. The wear rate increase and friction coefficient present different variation trends with increasing load. For A356-20%SiCP composite, when the load is less than 10 MPa, wear rate and friction coefficient under sliding speed of 400 rpm are lower than those of 200 rpm. Wear mechanism transition from abrasion, oxidation, delamination, adhesion to plastic flow as load and sliding speed increasing.
Practical implications
Results of this study will help guide the use of A356-SiCP in many automotive products such as brake rotors, brake pads, brake drums and pistons.
Originality/value
There are few paper studies the effect of particle content, applied load and sliding speed on the tribological properties of A356-SiCP composites. Aluminum matrix composites with uniform distribution of reinforcing particles were successfully prepared by using the newly developed vacuum stir casting technique.
Purpose
This study aims to understand the multiaxial fretting fatigue, wear and fracture characteristics of 35CrMoA steel under the elliptical loading path.
Design/methodology/approach
By keeping the contact pressure and torsional shear cyclic stress amplitude unchanged; the axial cyclic stress amplitude varied from 650 MPa to 850 MPa. The fretting fatigue test was carried out on MTS809 testing machine, and the axial cyclic strain response and fatigue life of the material were analyzed. The fretting zone and fracture surface morphology were observed by scanning electron microscope. The composition of wear debris was detected by energy dispersive X-ray spectrometer.
Findings
In this study, with the increase of axial stress amplitude, 35CrMoA steel will be continuously softened, and the cyclic softening degree increases. The fretting fatigue life decreases unevenly. The fretting scars in the stick region are elongated in the axial direction. The area of fracture crack propagation zone decreases. In addition, the results indicate that wear debris in the slip region is spherical and has higher oxygen content.
Originality/value
There were few literatures about the multiaxial fretting fatigue behavior of 35CrMoA steel, and most scholars focused on the contact pressure. This paper reveals the effect of axial cyclic stress on fretting fatigue and wear of 35CrMoA steel under the elliptical loading path.
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