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Nitriding is a thermochemical surface treatment that is often utilized to improve the fatigue strength of mechanical elements. In fact it is well known that, after the treatment, owing to the formation of a nitrided external layer and a field of residual stresses that are compressive on the surface, the high-cycle strength is strongly increased. Treatment characteristics include temperature and duration, whose values are generally decided by the operator. In this study, experimental axial tests were conducted on smooth specimen groups, which were each treated by using different durations. The results ow- the strong influence of treatment time on the elastic modulus values: in particular, if the duration increases, the elastic modulus increases too. A simple model allowed us to evaluate the distribution of the stresses in the case and in the core, and it was found that by increasing the treatment time the external layer is more stressed with respect to the core. Low-cycle fatigue was investigated, and the ϵa−Nf curves obtained by means of the differently treated specimens were compared. The results show that increasing the duration decreases the fatigue behaviour for high applied strains, and only one overload may be sufficient to fracture the external layer.

In this paper the problem of predicting and optimising the fatigue strength of shot peened specimens is dealt with. A series of notched cylindrical specimens, peened by using different parameters, was fatigue tested, being the aim to determine the improvement of the fatigue limit of the treated specimens. After the tests, the specimens were observed at the SE microscope and non-propagating microcracks were found. On the basis of this experimental evidence it was considered that the fatigue alleviation due to shot peening is mainly due to the ability of stopping crack propagation. A finite element procedure of the cracked notched specimens was established, with the aim of calculating the stress intensity factor including the applied load, the residual stresses and the contact between the crack faces. The results enable the prediction of the improvement of fatigue strength due to shot peening.

Differential scanning calorimetry has been carried out on native nuclei and intact cells from rat liver before and after partial hepatectomy in the temperature range between 320 and 410 K. Heat capacity profiles, properly background subtracted by means of a computerized system for data acquisition and analysis, reveal six and four thermal transitions respectively for the G0 cells and G0 nuclei. Following the induction of cell proliferation a significant enthalpy redistribution takes place among the various transitions. By comparison with the melting enthalpy and temperature for each transition being present in isolated nucleohistone, DNA, RNA and proteins and by the effect of selective enzyme digestions, unique assignment of the various transitions appears possible, pointing to a unique sequence of chromatin conformational changes following the induction of cell proliferation and prior to DNA replication. Results are discussed in terms of membrane proteins, cytoplasmic RNA and of secondary, tertiary, quaternary and quinternary DNA structures.

Dealing with composites in polymeric matrix, the pultruded ones are among the more suitable for large production rates and volumes. For this reason, their use is increasing also in structural applications in civil and mechanical engineering. However, their use is still limited by the partial knowledge of their fatigue behaviour; in many applications it is, indeed, required a duration of many millions of cycles, while most of the data that can be found in literature refer to a maximum number of cycles equal to 3 millions. In this paper a pultruded composite used for manufacturing structural beams is considered and its mechanical behaviour characterized by means of static and high-cycle fatigue tests. The results allowed to determine the S-N curve of the material and to assess the existence of a fatigue limit. Observations at the scanning electronic microscope (SEM) allowed to evaluate the damage mechanisms involved in the static and fatigue failure of the material.

— The problem of fatigue crack propagation in surface treated specimens similar to gear teeth is analysed. Experimental fatigue tests were carried out on carburized, and carburized and shot peened, specimens. In order to predict crack propagation and to consider the effect of the treatments, different models of the cracked specimens were realized. Two numerical approaches were followed: the finite element method and the weight function technique. Two- and three-dimensional finite element models were constructed, and the stress-intensity factors were evaluated by considering the effect of both the load and the residual stresses due to the treatments. The agreement between these and those obtained through the weight function technique is good. The weight function approach was used directly in the computer software package (which allows crack propagation predictions) and considered the effects of hardness and residual stresses. The comparison between theoretical predictions and experimental results validated the approach followed.

The problem of the rolling contact fatigue crack propagation in gear teeth is dealt with. An approach based on the weight function method for the determination of KI and KII of internal cracks was developed. The effect of the contact and of the friction between the crack faces was taken into consideration by using approximate relations. The results were compared with the ones obtained by finite element analyses and the agreement was found satisfactory. By means of the determined weight function several analyses were performed and an interpolating function of KII versus the crack length were found. An approach for rolling contact fatigue crack propagation prediction based on the obtained solution and on a short crack propagation law was developed and implemented in a computational routine. The results are critically discussed.Copyright © 2003 by ASME

Computational and experimental studies were performed in order to investigate the propagation of cracking in a spur gear tooth. The stress intensity factors were numerically calculated by the definition of weight functions and by finite element analysis. The influence of the hardness and the residual stress was evaluated and a computational procedure, based on crack tip opening displacement, was defined in order to assess the crack closure effect. Different propagation laws were adopted and life predictions were made. Experimental results were obtained by using special equipment with which it is possible to carry out fatigue tests on gear teeth. These results were compared with the life predictions. The comparison clearly indicates the importance of residual stresses, hardness and, particularly when the loads applied are lower, the crack closure effect.

Solid tumors develop resistance to retinoids during carcinogenesis. One of the strategies to overcome this resistance may include the combination of these molecules with other differentiating, cytotoxic or chromatin-remodelling agents. We analysed the anti-proliferative activity of two histone-deacetylase inhibitors (HDACIs), Trichostatin A (TSA) and sodium phenylbutyrate (PB), alone or combined with retinoids, all-trans retinoic acid (ATRA) and Ro 41-5253, on two human breast cancer cell lines: the hormone-dependent MCF-7 and the hormone-independent MDA-MB-231. These lines responded differently to retinoids: MCF-7 were sensitive, whilst MDA-MB-231 were rather resistant. When the retinoids were combined with HDACIs, these molecules potentiated the retinoid activity on growth inhibition, especially for the association Ro 41-5253 and TSA. By FACS analysis, we observed that the anti-proliferative effects were only partially due to pro-apopotic mechanisms, suggesting a cell-cycle block. The efficacy of the retinoids/HDACIs combinations could represent a new strategy in breast cancer chemotherapy, allowing inhibition of both ER + and ER- cell populations.

In this paper, an elastic plastic behaviour model based on internal state variables is investigated. The final aim is to describe the mechanical stress-strain cyclic response of oxide dispersion strengthened (ODS) steels during the cold pilgering process. In this tube forming operation, a material element undergoes a series of small incremental deformations, alternatively under tensile and compressive stresses. The cyclic model considers isotropic hardening and kinematic hardening which can be related to the typical continuous cyclic softening of the ODS steels. Moreover, the identification process of the cyclic model parameters involves experimental data from only one sample. ODS steels tubes usually reveal an anisotropic strength in the radial, ortho-radial and longitudinal directions due to a crystallographic and strongly elongated grain morphology in the rolling direction. Identification of 3 Hill's parameters is done using compression tests of cylindrical specimens cut in three different directions (longitudinal, radial and ortho-radial) combined with an inverse analysis. © 2011 Published by Elsevier Ltd.