Failure Analysis in Graphite Epoxy Composite Laminates

The present analysis was performed to obtain bearing strength for pinned joints in uni-directional graphite epoxy composite laminates using characteristic curve model. The characteristic dimensions used to determine the characteristic curve were evaluated using a two-dimensional finite element model that was developed in ANSYS14.5 Software. Also, two-dimensional finite element stress analysis was developed to determine the stress distribution needed to evaluate the failure. Tsai-Wu failure criterion was used in the analysis with the characteristic curve to predict bearing strength. The results of the analysis showed good agreement with experimental data.

Strain-induced formation of a gradient nanostructured surface layer on an ultrahigh strength bearing steel

In the present work, an ultrahigh strength bearing steel（AISI 52100） was subjected to surface mechanical rolling treatment（SMRT） at room temperature. Microstructural observations showed that martensitic laths, twins and cementite particles in the initial microstructure underwent distinct plastic strains and were gradually refined into nanostructures. Consequently, a gradient nanostructured（GNS） surface layer with a mean grain size of -24 nm at the top surface was obtained on the bearing steel, resulting in an increment of -20% in the surface hardness. Analyses based on microstructural evolution, phase constitution and in-depth hardness distribution revealed a mechanically induced formation mechanism of the GNS surface layer. The multiple surface severe plastic deformation under fine lubrication and cooling during SMRT contributed to the formation of a thick hardened surface layer on the bearing steel.

Damage propagation and strength prediction of a single-lap interference-fit laminate structure

Experimental and finite element research was conducted on the bolted interference fit of a single-lap laminated structure to reveal the damage propagation mechanism and strength change law. A typical single-lap statically loading experiment was performed, and a finite element damage prediction model was built based on intralaminar progress damage theory. The model was programmed with a user subroutine and an interlaminar cohesive zone method. The deformation and damage propagation of the specimen were analyzed, and the failure mechanism of intralaminar and interlaminar damage during loading was discussed. The effect of secondary bending moment on load translation and damage distribution was revealed. The experimental and simulated load–displacement curves were compared to validate the developed model’s reliability, and the ultimate bearing strengths under different fit percentages were predicted. An optimal percentage was also recommended.

Quantitative characterization of damage-aggravation effect caused by progressive damage

Aiming at the progressive damage phenomenon in geotechnical field,it attempts to study the effect of progressive damage on the macro-bearing capacity.Firstly,based on the theoretical analysis of a two-dimensional plane inside representative volume element,it is proposed that progressive damage will occur if the bearing capacity of microplanes is different.Besides,“damage-aggravation effect”is proposed according to the difference between the macro-bearing capacity of entire plane and the sum of bearing capacity of all microplanes when progressive damage occurs.Secondly,progressive damage ratio K_(t)is proposed to quantify“damage-aggravation effect”.Finally,based on the rod model,the correspondence between K_(t),and some influence factors is studied by theoretical analysis and numerical simulation.The results show that“damage-aggravation effect”does exist,and the macro-bearing capacity of entire plane is less than the sum of bearing capacity of all microplanes when progressive damage occurs.If the bearing capacity of rods in the rod model obeys uniform distribution,as the minimum of bearing capacity increases linearly,the macro-bearing capacity increases linearly,and K_(t)decreases inversely.