Key Engineering Materials Vols. 577-578

Abstract: Pounding between insufficiently separated buildings, which may result in considerable damage or may even lead to the total collapse of colliding structures, has been repeatedly observed during earthquakes. Earthquake-induced collisions of buildings has been intensively studied applying various structural models. It was assumed in the analyses, however, that the seismic excitation is identical for all structural supports; whereas, in the reality, the ground motion differs from place to place due to spatial seismic effects connected with propagation of the seismic wave. The aim of the present paper is to conduct a detailed non-linear damage-involved analysis of pounding between two structures under non-uniform earthquake loading. A case of pounding between the Olive View Hospital main building and one of its stairway towers, observed during the San Fernando earthquake of 1971, has been considered in the study. In the numerical FEM analysis, non-linear material properties have been simulated using stiffness degradation (due to damage under cyclic loading) model of concrete and elastoplastic damage model of reinforcing steel. A method of conditional stochastic modelling has been used to generate the input ground motion records. The results of the study indicate that the incorporation of the non-uniform ground motion excitation may lead to substantial change of pounding-involved response of the structures. The difference between the uniform and non-uniform responses has been found to be relatively large considering the fact that the variation in the simulated input ground motion records was rather small. This shows the importance of incorporation in the damage-involved numerical analysis the effects connected with propagation of the seismic wave.

Abstract: The corrosion environments of individual parts of members in a steel structure vary significantly. Therefore, efficient maintenance requires accurately evaluating these environments and predicting corrosion damage over time. This research focused on comprehensively evaluating the corrosive environment of each part of members in the structures based on the mean corrosion depth of uncoated steel plates mounted on the members. Atmospheric exposure tests were conducted in four exposure fields in which the environments varied widely as a function of rainfall and airborne sea salt. Based on the test results, a practical method of estimating the mean corrosion depth using the thickness of the corrosion-product layer on the mounted plates that does not require removal of the corrosion product is proposed. Furthermore, a method for estimating the time-dependence of corrosion depth for parts of the members after deterioration of the paint coating is proposed.

Abstract: Vibrated concrete (VC) and self-compacting concrete (SCC) have a substantially different composition, resulting in dissimilar mechanical properties regarding cracking behaviour. The critical value of the mode I stress-intensity factor K_IC is an appropriate fracture parameter for evaluating fracture toughness and can be obtained from three-point bending tests (3PBT) on small, notched specimens. Subsequent determination of the energy release rate thus allows to examine the crack propagation and fracture process of both concrete types. This paper describes the results of such 3PBTs on samples, made from VC and SCC. Evaluation of the cracking behaviour, derived from these results, reveals remarkable differences.

Abstract: Composite laminates meanwhile are of common use, especially in aerospace engineering. Inter-fiber cracks within a laminate ply are often accepted in practice to be still within failure tolerance, although the structural mechanics of this situation is not fully understood. The situation gets even more complex when the interaction of inter-fiber cracks in neighboring plies is considered. In this work, such three-dimensional crack configurations in composite laminates involving inter-fiber cracks and the influence of the laminate free-edge effect are studied by means of the Scaled Boundary Finite Element Method (SBFEM). The SBFEM is an efficient semi-analytical method that permits the analysis of linear elasticity problems including stress singularities or infinite domains. It is shown that in crack configurations in composite laminates so-called hypersingularities (or supersingularities) can occur, i.e. stress singularities which are of higher order than the classical crack singularity. This indicates that the laminate failure risk induced by certain considered crack configurations is not to be underestimated.

Abstract: The simultaneous effect of crack length and crack front shape on plasticity-induced crack closure (PICC) for a 304L austenitic stainless steel is simulated through 3D numerical modelling using finite element software Abaqus for through-thickness cracks with different curved crack fronts in CT specimens in comparison with bidimensional through crack with a straight front. The influence of possible loading history effect is avoided by applying constant K amplitude. The local stress intensity factor range for crack opening K_op is evaluated from the simulation of the loss of the last local contact between the crack lips near the crack tip. The pertinence of the different crack front shapes is discussed in term of the effective stress intensity factor range K_eff and in comparison with the experimental crack front observations.

Abstract: In the present experimental work, a WC/C coated 7075-T6 aluminum alloy was considered from the corrosion point of view. The coating was deposited by PVD technique with a final thickness of about 2.5μm. In order to study the influence of the coating on the corrosion behavior of the aluminum alloy, the samples surfaces were partially coated and the interface among the metal and the coating was analyzed after the corrosion tests described into the ASTM G110 standard. Such experimental plan was decided in order to simulate the possible in-service local removal of the thin and hard coating. This kind of damage, due for example to a foreign object impact, can occur because of the great hardness difference between the coating and the substrate. The experimental tests were carried out on samples with different surface finishing, ranging from about 0.02μm Ra (mirror-polished surface) to about 0.8μm Ra (320 grit paper). The aim of such choice was to investigate the effect of a surface roughness different from the optimal one (mirror polished) on the coating deposition. Moreover a different corrosion resistance is expected.

Abstract: 7075-T6 is one of the most performing aluminium alloys, considering its mechanical properties and good fatigue behaviour. In this work the influence of WC/C and DLC PVD coatings on the fatigue behaviour was investigated by rotating bending tests at 2·10⁵ cycles. The fatigue behaviour of polished and untreated specimens was considered as reference. In order to decouple the effect of the deposition temperature from the coating one, some uncoated specimens were submitted to the thermal cycles of the WC/C and DLC processes and then tested under fatigue loading. Fatigue life was determined using a step-loading technique. SEM micrographs of the fracture surfaces were taken in order to characterize the fatigue mechanisms of coated and uncoated specimens.

Abstract: It is Common Practice for Polymer-Metal Interfaces, Frequently Encountered in Microelec-Tronic Devices, to Improve Adhesion by Surface Roughening or Micro-Patterning. the Competitionbetween Adhesive Fracture and Cohesive Fracture in the Vicinity of a Patterned Interface, i.e., Inter-Face Crack Deflection, is One of these Key Mechanisms that Contribute Significantly to the Macroscopicadhesion. in this Paper, these Fracture Phenomena are Described Simultaneously by Cohesive Zoneelements with an Exponential Traction-Separation Law (TSL) for the Adhesive Failure and an Initiallyrigid, Exponentially Decaying, TSL for the Cohesive Failure. it is Demonstrated that the Conditions Atwhich Crack Kinking Occurs are Dominated by Fracture Strength Values as Opposed to the Commonlyused Fracture Toughness Values. Experimental Verification is Performed by Means of Four Point Bend-Ing Tests on Specifically Designed Micro-Patterned Polymer-Metal Samples.

Abstract: Advancements in the numerical modelling of 3D woven composites have allowed improved understanding of the mechanical behaviour and in turn aided the design and analysis of new materials. The objectives of this paper are to utilise FEA (Finite Element Analysis) methods to determine the elastic properties of a given woven composite. The investigation focuses on satin weaves, considering both 5-harness and 8-harness varieties. Multi-scale analysis results of an RVE are used to formulate the stiffness matrix and consequently determine the elastic properties; these will be compared to published analytical methods and experimental results. Further investigations considering the effect of weave parameters on the elastic properties are conducted.

Abstract: A 3D grain-level formulation for the study of brittle failure in polycrystalline microstructures is presented. The microstructure is represented as a Voronoi tessellation and the boundary element method is used to model each crystal of the aggregate. The continuity of the aggregate is enforced through suitable conditions at the intergranular interfaces. The grain-boundary model takes into account the onset and evolution of damage by means of an irreversible linear cohesive law, able to address mixed-mode failure conditions. Upon interface failure, a non-linear frictional contact analysis is introduced for addressing the contact between micro-crack surfaces. An incremental-iterative algorithm is used for tracking the micro-degradation and cracking evolution. A numerical test shows the capability of the formulation.