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The crack tip blunting and re-sharpening on the crack tip is one of the basic mechanisms for fatigue crack growth in ductile metals and alloys, e.g. Laird [ 1 ], Neumann [ 2 ]. Previous numerical studies of crack tip blunting made by Mc Meeking [ 3 ], Needleman and Tvergaard [ 4 ] have been carried out for monotonic loading. Subsequently, this kind of analysis has been made for cyclic loading (Gu and Ritchie, Tvergaard and Hutchinson [ 5 ]), for the load ratio R=0. It is shown that is possible to obtain fatigue crack growth, which can be comparable with Paris law. Perfect plasticity and a finite element mesh with a small initial radius of the crack tip were used. Because of strong mesh distortion they were applied only three full cycles.

The Charpy impact test is widely used to monitor the quality requirements of industrial processes. It was also adopted by engineers and scientists to monitor material embrittlement resulting from environmental effects like for example irradiation. In this work, we investigated the effect of loading rate, namely quasi-static versus impact loading, on the ductile fracture behavior. Two low alloyed steels used in the reactor pressure vessel industry were selected, namely A533B and 20MnMoNi55. These steels were extensively characterized from the flow, Charpy impact and fracture toughness properties [ 1 ]–[ 2 ]. Figure 1 shows how the loading rate affects the ductile to brittle transition curve for both materials. As can be seen, the major effect of loading rate is located in the fully ductile regime where quasi-static loading requires significantly less energy to full fracture than dynamic (impact) loading. Two temperatures, namely 25°C and 290°C were selected to investigate these loading rate effects. At both temperatures, tensile and crack resistance measurements were performed at both quasi-static and dynamic loading. For the A533B steel, at 25°C, the fracture is not fully ductile and therefore only tests at 290°C were considered for this material. The results are shown in Table 1 for the various materials and conditions. These result clearly show that empirical correlations [ 3 ] relating fracture toughness to Charpy impact energy are not applicable without an in-depth analysis. Moreover, the loading rate effects on the crack resistance cannot be solely attributed to the strain rate sensitivity of the material.

Although the enormous progress in fatigue investigations and the understanding achieved during the last years, fatigue phenomenon stays as an important problem concerning strength of metals, their life and structural integrity of engineering constructions. One method which is very useful, informative and easy for application is that of investigation of short fatigue-crack growth by replica monitoring of surface crack propagation from the initiation to failure. In our case, this method includes short-crack rotation-bending (R-B) experiments and length measuring of propagating crack a at some cycles N on smooth hour-glass specimens subjected to different frequency and symmetric cycling loading, Table 1. Material under investigation is a rolled lowcarbon, low alloyed steel (RLCLAS), mostly used for off-shore applications and in shipbuilding, marked as 092 according to the Bulgarian Construction Steel Standard. Experimental conditions under in-air R-B are the following: specimen 1 (Stress range, MPa — 620, Frequency f , Hz — 11), and respectively: specimen 2 (620, 11), specimen 3 (580, 11), specimen 4 (620, 6.6).

Heavily loaded structural components may present local yield at stress concentrators, such as, notches and geometrical discontinuities [ 1 ]. In cases involving cyclic loads, the presence of local plasticity could lead to the nucleation and propagation of fatigue cracks and complete fracture of the components [ 2 , 3 ]. In such cases, the strain life approach should be used to evaluate fatigue damage, making it necessary to perform an elastoplastic analysis of stresses and strains at the proximities of these stress concentrators. Due to reduced computational effort requested, approximated models are widely used with that purpose. The most used are the ones proposed by Neuber [ 4 ], Seeger et al. [ 5 ], Glinka [ 6 ] and Ye et al. [ 7 ].

In order to study the fatigue behavior of 6000 aluminium alloy welded structures and to take into account the small size of the affected zone, a specific heat treatment was developped to get a structure equivalent to that of the heat affected zone (simulated HAZ). Such an equivalent structure was determined by comparing their hardness, microstructure and tensile properties. A new cumulative damage law has been developed taking in account the loading history.

An AFM technique established for observing two types of fine and complicated tempered martensite structures was developed into a technique for quantitatively evaluating local plastic deformation near tensile yield points. Surface steps with 5–40 nm were observed in locally deformed martensite blocks near prior austenite grain boundaries.

Magnesium (Mg) alloys are very attractive materials for structural applications because of excellent specific strength. However, their absolute strengths are insufficient, thus it is necessary to further improve the mechanical properties, particularly fatigue strength. One of the methods for improving mechanical properties is grain refinement, but studies on grain refinement in Mg alloys are very limited (Yamashita et al. [ 1 ], Kumar et al. [ 2 ]). The purpose of the present study is to achieve grain refinement due to controlled extrusion and associated improvement of fatigue strength in wrought Mg alloys. First, grain refinement due to extrusion was studied and then the fatigue behaviour of the extruded materials was discussed.

The use of PMMA bone cement is the most successful way of fixing implants such as hip and knee replacements, and has many other uses in orthopaedic surgery. However, in the long term mechanical failure of the cement is common and may lead to clinical failure. Despite a large volume of published research, the fatigue of bone cements is not well understood and much more research is needed before fatigue failure can be reliably predicted and avoided.

Ceramic thermal barrier coatings are commonly used in gas turbine hot components ( e.g. , combustor liners/buckets and guide vane platforms). In components that are only partially coated or have cooling-air outlets, coating-end stress singularities may lead to the spallation of the coating.

The strength of a composite material in form of laminate is obtained from the properties of the constituent laminae. The interface between different laminae is an important factor since it influences the stresses which are developed in the laminate and hence the strengths.