Abstract: The aim of this study was to analyze the effect of successive TIG (tungsten inert gas) welding repairs on the reverse bending fatigue strength of AISI 4130 steel, which is widely used in components critical to the flight-safety. In order to simulate the abrupt maneuvers, wind bursts, motor vibration and helixes efforts, which generate cyclic bending loadings at the welded joints of a specific aircraft component called "motor cradle", experimental reverse bending fatigue tests were carried out on specimens made from hot-rolled steel plate, 1.10 mm (0.043 in) thick, by mean of a SCHENK PWS equipment, with load ratio R = -1, under constant amplitude, at 30 Hz frequency and room temperature. It was observed that the bending fatigue strength decreases after the TIG (Tungsten Inert Gas) welding process application on AISI 4130 steel, with subsequent decrease due to re-welding sequence as well. Microstructural analyses and microhardness measurements on the base material, heat-affected zone (HAZ) and weld metal, as well as the effects of the weld bead geometry on the obtained results, have complemented this study.
Abstract: Many components can reach or exceed 109 cycles in their service time. When fatigue life is beyond 106, the Wöhler S-N curve was always considered to be asymptotic in horizontal axis, but the fatigue behaviour over 106 cycles can not be neglected. It is not usual to carry out a fatigue test beyond 109 cycles due to the conventional fatigue test’s constraints, time consuming and expensive. High strength steel is widely applied in automobile, railway industry after surface treatment in order to improve performance of material in practice. Carburizing process hardens surface to increase wear and fatigue resistance and shot peening has a beneficial effect on the material fatigue strength from the surface residual compressive stresses. A piezoelectric gigacycle fatigue machine is used to do the tests in gigacycle regime on specimens with different surface treatments. The effect of different surface treatments is investigated in gigacycle regime at a frequency of 20KHz with a fixed stress ratio R=0.1 at room temperature. Moreover, Scanning Electron Microscopy (SEM) observations of fracture surfaces are analyzed to evaluate the mechanism of damage related to surface treatments, microstructure scored inclusion size. The role of inclusions and microstructure is emphasized at 109 cycles.
Abstract: A test methodology is employed to investigate the cutting behaviour of five different diamond impregnated tools for cutting hard materials, such as rocks. A set of parameters, which characterise the tool wear (specific wear loss in the tool), and its relationship with the cutting force of the examined tools, are established to evaluate the tool wear performance. The procedure established in this work describes the specifications of the equipment used to carry out the tests, the different cutting conditions, the format of the output parameters and the characterisation of the different materials used (binders and rocks), hence allowing to discuss the overall cutting wear behaviour of the tools. The methodology presented indicates a universally applicable procedure for measuring the wear performance of the diamond tools as, at the same time, it establishes a relationship between wear and the mechanical parameters of the different metallic binder materials used to manufacture the correspondent tools. The procedure is proven to be an indispensable instrument for correctly carrying out wear performance tests and for reliably interpreting the wear mechanisms of the tool.
Abstract: The creep degraded nickel base single crystal superalloy CMSX-4 of two axial orientations  and  was investigated with aim to assess the structure degradation. Constant load creep tests were conducted in the stress/temperature ranges of 250–780 MPa/750 – 50°C resulting in rupture time variation from 50 to 4000 hours. A combination of scanning electron microscopy (SEM) and non-destructive small-angle neutron scattering method (SANS) was used to investigate the directional coarsening (rafting) of the gamma prime (γ') precipitates in relation to the stress and temperature applied as well as to the initial crystallographic orientation of the specimens. The SANS results are discussed in terms of the correlation with the raft development, the axial orientation of specimen, the creep parameters and the mechanical properties.
Abstract: Among various coatings for industrial and engineering applications, vitreous enamel ones have advantages of chemical inertness, high temperature stability and superior mechanical properties with reference to abrasion or impact as a comparison to other coating materials applied by thermal spraying. The enamelled composite, due to its internal composition, functionalization and architecture can be considered as a functionally graded composite material. In the present work, a first systematic characterization of the mechanical behaviour of enamelled steel sheets is presented. Tests were performed under four-point bending load with displacement control and acoustic emission monitoring. The mechanical response of tested materials was used to determine some key elastic parameters (e.g. Young Modulus), and the First Crack Failure parameter. Moreover, the mechanical performance of tested coated specimens was also related and discussed with reference to microstructure, surface characteristics, and residual strains in the coated structure.
Abstract: The fracture behaviour of brazed joints of the soft martensitic stainless steel X3CrNiMo13-4 under cyclic loading is investigated. The fatigue crack propagation curves (da/dN-ΔK) were derived for different load ratios R. The fatigue crack threshold values ΔKth were estimated to be 9 MPa m0.5, 7 MPa m0.5, 6 MPa m0.5 and 4 MPa m0.5 for the R values of 0.1, 0.3, 0.5 and 0.7, respectively. In addition, crack growth curves were derived for different constant loads ΔF. The Paris exponent, n, was estimated for the different R values and found to be very high compared to homogeneous materials. The work was completed with microstructural and fractographic investigation by scanning electron microscope (SEM).
Abstract: This paper focused on the tensile performance of PVC-coated membrane materials under multi-axial loads. Several groups of experiments were carried out to investigate the effect of the specimen configuration and the loading speed on the tensile properties. It could be concluded that the configuration of the specimen plays an important role on the tensile performance of the materials. The suitable configuration for multi-axial loading tests had been identified. It was also found out that the loading speed had certain effect on the tensile failure performance and the tensile response. A loading speed of lower than 20mm/min was suggested to achieve a reasonable result of the multi-axial tensile performance of PVC-coated membrane materials. Another group of tensile experiments with a crack in the center of the specimens under multi-axial loads were performed. It was noticed that the tensile properties in warp direction of the coated membrane materials play an important role in the tensile failure under multi-axial loads, no matter the initial crack length and the crack orientation are.
Abstract: The testing setups, results and analysis of constant load creep and low-cycle high temperature fatigue tests of tungsten inert gas (TIG) butt-welded, thin-section INCONEL 718 (IN718) specimens are presented. The main objectives were to determine the effect the welds have on failure time and analyse any differences in their failure behaviour. It was found that although welded IN718 may exhibit comparatively little loss of tensile strength, its ductility and creep and high temperature fatigue properties are severely compromised due to its changed microstructure.
Abstract: Tensile and fatigue crack growth tests of the 6056 T651 and T6 aluminium alloys were carried out. The fatigue crack propagation tests were performed on compact tension 4mm thick (CT) specimens, under cyclic loading with R ratios 0.1 and 0.5. The resulting data was used to predict the fatigue behaviour of stiffened panels subjected to fatigue loading under similar R ratios. The AA6056-T651 panels were fabricated using High Speed Machining (HSM) starting with 30mm thick plates. AA6056-T651 CT specimens were cut from the panels mentioned above, whereas AA6056-T6 CT specimens were machined from 5mm thick material. It was found that the AA6056-T651 (HSM material) specimens, machined from a 30mm thick plate presented higher rupture and yield stress than the AA6056-T6 material extracted from a 5mm thick plate. When tested at the same R value the AA6056-T6 specimens present higher crack growth rate than the AA6056-T651 specimens.
Abstract: The interlaminar fracture toughness in pure mode II (GIIc) of a Carbon-Fibre Reinforced Plastic (CFRP) composite is characterized experimentally and numerically in this work, using the End-Notched Flexure (ENF) fracture characterization test. The value of GIIc was extracted by a new data reduction scheme avoiding the crack length measurement, named Compliance-Based Beam Method (CBBM). This method eliminates the crack measurement errors, which can be non-negligible, and reflect on the accuracy of the fracture energy calculations. Moreover, it accounts for the Fracture Process Zone (FPZ) effects. A numerical study using the Finite Element Method (FEM) and a triangular cohesive damage model, implemented within interface finite elements and based on the indirect use of Fracture Mechanics, was performed to evaluate the suitability of the CBBM to obtain GIIc. This was performed comparing the input values of GIIc in the numerical models with the ones resulting from the application of the CBBM to the numerical load-displacement (P-) curve. In this numerical study, the Compliance Calibration Method (CCM) was also used to extract GIIc, for comparison purposes.