Key Engineering Materials Vols. 488-489

Abstract: In this paper polymer particulate composite was studied. The composite was modeled as a three-phase continuum – soft matrix, interphase and rigid particles. On the basis of fracture mechanics methodology the interaction of micro-crack propagation in the soft matrix filled by rigid particles (covered by the interphase) was analyzed. The properties of soft matrix (elasto-plastic material) were determined from the experiment and they were used for estimations of the crack behavior.

Abstract: Methodology is suggested for calculation of effective elastic constants of layer containing intralaminar cracks. Trends are presented for layers with low and medium high crack densities, where the interaction between cracks can be neglected. The effective properties of the damaged layer are determined by back- calculation using previously developed GLOB-LOC model for thermo-mechanical properties of damaged laminate [1]. It is shown that the effective transverse modulus and shear modulus of a layer decrease linearly with increasing crack density, whereas longitudinal modulus and major Poisson’s ratio do not change at all. Experimental data for multiple cracking are analyzed showing that linear approximation of crack density versus applied strain may have sufficient accuracy. These two linear trends are used to calculate the effective elastic properties of a layer as a function of strain.

Abstract: Defect size of wall thinned pipe is measured by using Speckle Shearing Interferometry (SSI) and Digital Image Correlation (DIC) techniques. A wall thinned defect of a carbon steel pipe was typically caused by flow accelerated corrosion (FAC). As wall thinned pipe can cause a huge accident at the nuclear power plant (NPP), a wall thinned defect should be detected for structure safety. SSI is one of the optical nondestructive techniques and can provide to inspect in real-time and to measure on the whole visible area at a time. DIC is a kind of the visual testing method. This method which uses a stereo vision system can measure the deformation or strain/stress of a structure in 3D. In this paper, ASTM A106 Gr.B carbon steel pipe is used as specimen. When the pressure load is provided by the pressure pump, the out-of-plane deformation along the longitudinal direction of a pipe can be detected quantitatively. Both results of SSI and DIC experiments are compared.

Abstract: The problem of treatment parameter optimization focused on the fatigue resistance is analysed through a case study about Deep Cryogenic Treatment (DCT) of AISI 302 steel. In particular, the possibility to integrate fatigue data fittings through the Maximum Likelihood Estimation (MLE) method in the optimization process is evaluated. Two levels of two parameters (soaking time and temperature) are considered and then expanded to three by proper scaling of their values in order to include the untreated case as a “zero” level. Fatigue focused optimization is then achieved by standard Response Surface Method (RSM) and by MLE with two models for comparison purposes.

Abstract: This work focuses on the fatigue behaviour of notched Ti-6Al-4V titanium alloy in inert environment. V-notched flat samples were cycled under axial fatigue (R = 0.1) under inert conditions by immersion in paraffin oil. A step-loading technique was used to determine the fatigue limit at the complete fracture for a constant fatigue life of 2×10⁵ load cycles. The results were compared with previous data obtained with tests carried out in air and 3.5 wt.% NaCl solution. Fracture surfaces were examined under stereoscopic microscope.

Abstract: In this work a preliminary data set including experimental results from fatigue tests on smooth and foreign object damaged (FOD) aluminium samples coated with WC/C deposited with PVD (physical vapour deposition) technique was considered before testing WC/C-coated spur gears for racing motorcycles under rolling contact fatigue (RCF). The fatigue behaviour of the samples was correlated with the results obtained with the RCF tests on the coated gears. A special device mounted on a universal testing machine was used to carry out the RCF tests.

Abstract: Shot peening is a mechanical treatment usually performed on metals for improving the mechanical properties of the surface layers. The application of such treatment to sintered steels causes a local surface densification and the birth of residual compression stresses. In this paper, the effect of different shot peening cycles, selected after a preliminary optimization, has been investigated focusing especially on the fatigue resistance measured by bending tests and on the surface residual stresses measured by XRD technique. Two high performances PM steels were considered: the former was sintered starting from a diffusion bonded powder, whereas the latter is based on a pre-alloyed powder. Two different nominal densities were considered, 6.9g/cm³ and 7.1g/cm³.

Abstract: The bending properties of high strength precipitation-hardening AA6016-type Al alloy thin sheets in pre-aged T4P temper state were studied in this work. Microstructural features like grain boundary particles distribution and volume fraction of the matrix strengthening phases were considered as factors controlling the mechanical properties and the fracture of this grade. Remarkable decrease in ductility, accompanied by severe deterioration of bendability occurred when coarse precipitates were found into the grain boundaries. The in-situ fracture sequence investigations as well as the post-failure surfaces observations indicated that grain boundary ductile fracture mechanisms were involved in the propagation of the cracks during bending. Heat treatment simulations were carried out and the results showed that the precise control of the technological parameters during production of these sheets is the key factor responsible for obtaining an appropriate combination of strength and bendability. Only by providing both, homogeneous distribution of the matrix strengthening phases and a favourable grain boundary structure, the severe and often contradictory requirements for the functional properties of these alloys can be successfully satisfied.

Abstract: This paper presents the implementation of fatigue crack growth power law equations based on ΔK, ΔJ-integral and ΔCTOD fracture mechanics parameters determined in an FE analysis, to plates with multiple site damage (MSD). Results of fatigue tests with constant amplitude tensile loading carried out on mild steel plate specimens damaged with a single central crack and with three collinear cracks are presented. A relatively larger plastic zone occurred in the crack tip region at higher fatigue crack growth rate (FCGR), from 10^-7 to 10^-6 m/cycle. The crack growth models based on the elastic-plastic fracture mechanics (EPFM) parameters describe better fatigue crack growth in this range as compared to the liner elastic models.

Abstract: The concept of random tessellation is extensively used in wide area of natural sciences, especially material sciences. In this paper a simple but complete explanation of the random tessellation and mathematical tools requirements is presented. Then introducing the algorithm and the program for display random tessellation diagram was written. This program, with high speed and simple algorithm for random tessellation has the ability to change the level of statistical parameters such as number, mean, variance of the area of the grain. The ability to model microstructures of metals and grains for mechanical application, such as estimation of mechanical properties and crack propagation model in microstructure scale is very important. Finally, the microstructure produced by this program show good fitness of random generation with real microstructure.