Italian Group Fracture (IGF): E-Journals / Gruppo Italiano Frattura
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Effect of yield stress on fatigue crack growth
Get PDFAbstract. Fatigue crack growth (FCG) depends on loading, geometry and also material properties. Since FCG is supposedly linked to crack tip plastic deformation, material’s yield stress, Y0, is an important parameter. The main objective here is to develop a parametric study focused on the effect of Y0 on FCG. The study is based on the plastic CTOD, dp, determined numerically using the finite element method. The increase of Y0 was found to decrease dp, and therefore FCG rate. The variation is non-linear, being more important for lower values of Y0. The effect of Y0 was found to be much more relevant for the 7050 aluminium alloy than for the 304L stainless steel, which indicated a major influence of isotropic saturation stress. With the inclusion of crack closure, the reduction of dp is kept, but there is a substantial reduction of dp and therefore of FCG rate
Using a cohesive zone modeling to predict the compressive and tensile behavior on the failure load of single lap bonded joint
Get PDFThe detachment plates 2024T3 by an Araldite adhesive is studied in this work by using the finite element method to predict the damage in traction and compression behavior under the effect of geometrical parameters such as the lap length and the geometric shape of the plates called tapered. The numerical calculation is done by the ABAQUS calculation code. The adhesive has been modeled by an element of the cohesive zone CZM which takes part of the analysis in the first place on the influence of these parameters in mixed mode such as the critical energy and the maximum stress in opening and sliding. It is well shown that the behavior and parameters evaluated condition the resistance of our bonded structure to damage. The effect of these various parameters evaluated on the resistance is presented as results by failure load curves where each value represents an analyzed model
Experimental uncertainty budget for concrete compressive strength test based on a multifactorial analysis
Get PDFThe objective of the study is to introduce an experimental uncertainty budget process for concrete compressive strength test, based on a protocol that incorporates effects of multiple factors significant for the measurement result. The proposed procedure is rather useful for laboratories seeking accreditation according to ISO/IEC 17025, in order to emphasize the contribution of type A uncertainty estimations, rather than relying on type B estimations that are unable to address the correlation between those factors. Two independent experiments were performed. Experiment I is proposed as a simple, suitably designed, reproducibility trial for laboratories performing EN 12390 test method, i.e. when a specified nominal curing age is targeted, following experimental design on multiple uncertainty parameters. A sensitivity analysis was introduced based on a semi-empirical multifactorial regression model (experiment II) for concrete compressive strength as a function of specimen’s curing age and W/C ratio. The present study is an effort towards an integrated and standardized method for experimental, semi-empirical multifactorial regression estimation of the uncertainty budget for the EN 12390 test method, being useful, also, as a baseline for internal quality control programs when adjusted for the specific characteristics of concrete specimens tested by a laboratory
Experimental and numerical study on the influence of critical 3D printing processing parameters
Get PDFIn the present work the temperature profile variations generated in rectangular specimens built using the Fused Deposition Modeling (FDM) process, at different printing speeds and orientations, were investigated. The temperature recordings were achieved by the integration of temperature sensors throughout the 1st and/or 21st building layer of the specimens. The experimental results show that the temperature values inside the specimen re-main above the glass transition temperature (Tg) even at the end of the fabrication process. Higher values were obtained when increasing the printing speed and decreasing the printing path. The experimental results were compared to the corresponding ones derived by simulation of the thermal diffusion problem via Finite Element Analysis. The calculated maximum temperature values were in good agreement with the experimentally recorded ones
Double initial and caustic curves in diametrically compressed transparent discs - Application to the contact length
Get PDFGeneral formulae for double initial and caustic curves (reflected and transmitted) are obtained in the case of smooth contact of two cylindrical elastic bodies of arbitrary radii. Namely, based on the method of reflected and transmitted caustics, the conditions for the development of double initial and contact caustic curves are established as functions of six independent parameters, while easy-to-use closed-form expressions are given for obtaining the contact length. An experimental protocol is then implemented in the case a thin cylindrical transparent disc is compressed between the jaws of the International Society for Rock Mechanics suggested device for the execution of the Brazilian-disc test. The experimental method of caustics can provide the contact length quite accurately, even in the case of double curves which seem that are not always a consequence of a wide contact region
Use of by-products for partial replacement of 3D printed concrete constituents; rheology, strength and shrinkage performance
Get PDFIn this paper, fly ash, ladle furnace slag and limestone filler were utilized in concrete used as material for additive manufacturing (3D printing). Fly ash and ladle furnace slag were used as a replacement of cement (30% wt.) and limestone filler as a replacement of siliceous aggregates (50% wt.). Workability of fresh concretes that contained these by-products was measured 0, 15 and 30 minutes after mixing. Three different workability tests were conducted and compared: flow table, ICAR rheometer and an experimental method that measures the electric power consumption of the motor that rotates the screw extruder. Workability parameters that were measured were evaluated regarding printability of mixtures. Density, ultrasonic pulse velocity, compressive and flexural strength were measured on hardened concrete. Additionally, relative likelihood of cracking of different concrete mixtures was estimated by performing restrained shrinkage test (ASTM C1581). Results showed that use of fly ash or ladle furnace slag as binder, and limestone filler as aggregate decreases slightly the mechanical properties of concrete but improve its durability regarding cracking potential. Monitoring of electric power consumption of screw extruder motor was found to be an effective method for measuring easily real-time workability and define if a mixture is printable or not
Multi-response optimization of CuZn39Pb3 brass alloy turning by implementing Grey Wolf algorithm
Get PDFMachinability of engineering materials is crucial for industrial manufacturing processes since it affects all the essential aspects involved, e.g. workload, resources, surface integrity and part quality. Two basic machinability parameters are the surface roughness, closely associated with the functional and tribological performance of components, and the cutting forces acting on the tool. Knowledge of the cutting forces is needed for estimation of power requirements and for the design of machine tool elements, tool-holders and fixtures, adequately rigid and free from vibration. This work investigates the influence of cutting conditions on machinability indicators such as the main cutting force Fc and surface roughness parameters Ra and Rt when longitudinally turning CuZn39Pb3 brass alloy. Full quadratic regression models were developed to correlate the machining conditions with the imparted machinability characteristics. Further on, an advanced artificial grey wolf optimization algorithm was implemented to optimize the aforementioned responses with great success in finding the final optimal values of the turning parameters
Numerical Comparison of Cruciform weld and Butt weld simulation and a Study of Fracture Mechanics on Two Types of Welds
Get PDFThe modeling of the welding is desirable to guess the deformation of the components during manufacture, the position and the magnitude of maximum residual stresses and to envisage metallurgical effects in specific zones. The welding are problems of complex modeling requiring the thermal and structural solutions. This has to lead to the development of several software packages and codes for simulation by finite elements. The welding condition, the properties of the structure and their interactions have significant influences on the thermal and structural responses (temperature history, distortion, and residual stress) in welded structures. This paper presents a finite element procedure for the prediction of welding-induced residual stresses and distortions. Comparison is made with tow numerical example. The first example is a butt welded joint of two plates, while the second is a Cruciform welded joint of two plates with four passes. Moreover, a comparison between the Cruciform weld and the butt-weld which we can obtain the parameters of the linear fracture mechanics; stress intensity factor K and energy release rate G
Tension - torsion fatigue tests on the proton exchange membrane Nafion 115 (Perfluorosulfonic acid)
Get PDFBiaxial tension-torsion fatigue tests are carried out on the membrane material Nafion 115 (perfluorosulfonic acid, PFSA). This polymeric material is used in fuel cells as proton exchange membrane, undergoing frequently mechanical loading of tension and torsion during its industrial life. In order to carry out the fatigue tests on this polymeric material a self-designed and self-constructed machine was used, working under the following conditions: from 0 to 50 degrees of torsion, 0 to 60 MPa of initial tensile stresses, from room temperature (22 to 25° C) to 80° C, and two values for relative humidity: environmental and saturated relative humidity. All fatigue tests were carried out at the frequency of 1.2 Hz. This paper presents the first results, which concerns the following testing conditions: constant torsion angle of 50 degrees, 5 initial tensile stress of 60, 55, 50, 45 and 40 MPa, room temperature (22-25° C) and environmental humidity (50 – 60 %). The experimental results show that fatigue endurance decreases noticeably when the tensile stress increases. In the final section are presented the fracture surfaces observed by SEM, in order to investigate the principal trends of crack initiation and propagation under this modality of biaxial fatigue loading
Multi-axial fatigue numerical crack propagation in cruciform specimens
Get PDFTwo cracks, initiated from the opposite tips of a central notch inclined by 45°, were considered in cruciform specimens made of Ti6246. A static load was applied to a cruciform arm while a cyclic load was applied along the other arm.
Fatigue propagation of cracked specimens was performed by means of Dual Boundary Element Method (DBEM) and Finite Element Method (FEM) codes. For crack path assessment, the Minimum Strain Energy Density (MSED) and the Maximum Tensile Stress (MTS) criteria were adopted in DBEM and FEM approaches, respectively. Moreover, the J and M integrals’ formulations were used to evaluate the SIFs along the crack fronts for DBEM and FEM codes, respectively. Crack-growth rates were predicted by using a Walker law, calibrated on mode I fracture experimental data.
A good agreement between numerical and experimental crack paths was obtained