Key Engineering Materials Vol. 627

Abstract: The paper presents an analysis of the influence of the compressive (vertical) component of the loading force in the wedge splitting test on the values of fracture characteristics determined using standard procedures where this component is ignored. Particularly, a portion of work of fracture due to this compressive component of loading working on vertical displacements is investigated and given into relation with the common part of work of fracture calculated in the horizontal direction only. The results show that, based on the angle and width of the wedge used in the particular WST configuration, the portion of the work of fracture due to compressive loading can be considerable and should not be neglected.

Abstract: The paper describes the basic attributes of the new developed analytical method used for the calculation of corrosion losses on structural elements designed from weathering steels. The calculation takes into account the locality of the structure, type of the weathering steel, position and location of a surface in the structure and compliance with structural and maintenance requirements. The methodology for experimental testing of the realistic corrosion rates is introduced in this paper as well.

Abstract: 1D nonlinear model of a thin plate (or beam) with delamination was developed earlier. Large deflections and membrane strains of a plate in buckled state, as well as the strain energy described using elliptic integrals. The Griffith-type energy condition was used as a criteria of delamination propagation. The analysis of the destruction of the plate was performed depending on the geometrical dimensionless parameters of a plate and the material strength performance. Here the mentioned model is extended to the general mode of delamination and it allows to describe the post-buckling stage and damage propagation. Model application as a base for the alternative determination of the interlaminar fracture toughness of the layered composites is indicated.

Abstract: Silicon nitride based ceramics have received considerable attention during the last decades due to their very good room and high-temperature properties. Ceramics such as silicon nitride (Si₃N₄) are acknowledged as first choice for modern bearing applications. The influence of grain bridging on the strength and toughness was found. The prediction of crack propagation through interface elements based on the fracture mechanics approach and cohesive zone model is investigated from amount damage models. Using cohesive models the behaviour of materials is realized by two types of elements. The former is the element for classical continuum and the latter is the connecting cohesive element. Within the standard finite element package Abaqus the new finite element has been developed; it is written via the UEL procedure. The shape of the traction separation law for experimental materials is estimated from macroscopic tests, J–R curve is predicted and stability of the bridging law is tested. The shape of the bridging law is verified using the microindentation test, where the maximum crack length not exceeded 150 μm. The scope of the bridging effect is verified using the standard XFEM elements implemented in Abaqus.

Abstract: Continuous cyclic loading on concrete constructions involves a progressive cracking mechanism, leading to significant changes of the material properties during the lifetime of the structure. Gradually, irreversible damage is inflicted and the carrying capacity is affected, which may cause structural collapse at a stress or strain level much lower than in case of a single static load. This so-called fatigue phenomenon is well-documented in literature for traditional, vibrated concrete (VC), but this is not the case for self-compacting concrete (SCC). Given the fact that this latter concrete type is already used worldwide in many types of structures, including cyclically loaded ones, a good knowledge and understanding of the static and fatigue material behaviour is crucial. Up till now, it is unsure whether SCC performs better, worse, or equally under fatigue loading conditions. Therefore, in this study, destructive four-point bending tests are performed on large beams, made from VC and SCC, both statically and cyclically (at different loading rates). A comparison of the deflection, strain, crack pattern and crack width evolution of the different concrete types is made. The results reveal some significant differences regarding concrete strain and crack width development during the cyclic tests.

Abstract: Complex welded structures such as bridges are very often designed with the help of FE analysis. However, one should remain cautious when using such an analysis, since the results are mesh sensitive, with especially the mesh density and the element type influencing the results. In addition, these results are in most cases retrieved in hot spot areas with high stress gradients, where the maximum stress even cannot be correctly determined with linear elastic finite element analysis. For that reason, a stress evaluation method is required to obtain relevant stress levels that can be directly related to fatigue detailing. The most complete set of stress evaluation recommendations is given in the Recommendations for Fatigue Design of Welded Joints and Components from the International Institute of Welding. Nevertheless, several authors have recently commented on the difficulties regarding the application of these methods for the rib to floorbeam welds in orthotropic bridge decks. This paper provides findings for this type of connections based on both shell and solid model analysis and relates these findings to work from other authors.

Abstract: This paper presents an integrated creep-fatigue (ICF) theory to describe the non-linear creep-fatigue interaction during thermomechanical loading. The ICF theory recognizes the damage evolution as a holistic process consisting of nucleation and propagation of surface or subsurface cracks in coalescence with internally distributed damage, leading to final fracture. In a polycrystalline material under combined cyclic and dwell loading, crack nucleation and propagation occurs by fatigue or oxidation mechanisms, whereas internally distributed damage often occurs in the form of grain boundary cavities or microcracks due to creep or dwell effects, particularly at high temperatures. Based on the above mechanism, a damage evolution equation is mathematically derived, and the generality of the above physical mechanisms warrants the applicability of the ICF theory over a wide range of stresses and temperatures. This paper uses Mar-M 509, a cobalt base superalloy, as an example to illustrate how the ICF theory describes creep and low cycle fatigue (LCF).

Abstract: Stress fields in a single-domain sample of MMC containing multiple cracks in the ceramic layer are investigated using a direct analytical method and finite element modeling.

Abstract: This paper presents a FE² multi-scale framework for numerical modeling of the structural failure of heterogeneous quasi-brittle materials. The model is assessed by application to cementitious materials. Using the Continuum Strong Discontinuity Approach (CSD), innovative numerical tools, such as strain injection and crack path field techniques, provide a robust, and mesh-size, mesh-bias and RVE-size objective, procedure to model crack onset and propagation at the macro-scale.

Abstract: A major concern affecting the efficient use of carbon fibre reinforced composite laminates in the aerospace industry is the low velocity impact damage which may be introduced accidentally during manufacture, operation or maintenance of the composite structures. It is widely reported that the contact behavior of composite laminates under low-velocity impact can be obtained under quasi-static loading conditions. This paper focuses on the study of the correlation of the dent depth to the maximum contact force and damage of composite laminates under quasi-static loading. Analytical and finite element simulation approaches were employed to investigate relations between the contact force and the dent depth. Experimental investigations on the correlation between dent depth, maximum contact force and damage include quasi-static indentation testing, optical and scanning electron microscopic examination of the damage under different loading levels. The effect of damage initiation and growth on the contact behaviour has been discussed. Results show that consistent correlations between the dent depth, maximum contact force and damage exist and can be predicted with the analytical and numerical approaches. Dent depth can be used as an engineering parameter in assessing the severity of damage for composite structures that are subjected to low-velocity impact. This may lead to the development of a cost-effective technique for the inspection and maintenance of composite structures in aerospace applications.