Italian Group Fracture (IGF): E-Journals / Gruppo Italiano Frattura
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On the use of the stepped isostress method in the prediction of creep behavior of polyamide 6
Get PDFThe stepped isostress method (SSM) is an advanced technique which allows the prediction of the long-term behavior and enables the construction of creep master curves of materials with short-term experimental tests. However, the performance of this method is highly dependent on the numerical model and the time spent in data processing. In this paper, the effect of the extrapolation techniques on the creep curves trend is investigated using the SSM data of Polyamide test. Three extrapolation functions are used to offset the delay of the stress history: polynomial, power and exponential functions. Furthermore, a numerical routine is developed during the last step of the SSM, where the shift factors are computed taking into account the rescaling and the dwell times of each level of stresses. The processing of the SSM raw data has revealed that the rescaling parameters are the most determining factors to reach an accurate long-term creep curves. The rescaling process has shown an appropriate time, whether achieved by the exponential or power functions. Larger shift factors for exponential functions are assessed and therefore a long period of creep master curve was obtained
Interaction diagram for RC column strengthened by steel angles and strips
Get PDFThis paper presents an analytical model to construct the interaction diagrams (normal force and moment) for the RC column strengthened using the steel jacket technique. The proposed model is defined using the strain distribution block by determining the location of the neutral axis in the concrete section. The proposed analytical formulation is verified by experimental results performed by previous researches and numerical models using the nonlinear program ANSYS. The factors affecting the capacity of the strengthened column are taken into consideration, such as the amount of loads resisted by the steel cage, steel strips spacing, and the effect of concrete confinement. The results of the proposed model are in good agreement with the results from the experimental and numerical work used in verification. A practical design formula has been presented for strengthened columns
Recycling of plastic waste polyethylene terephthalate (PET) as a modifier in asphalt mixture: study of Creep-Recovery at Low, Medium, and Hot Temperatures
Get PDFOne environmental problem in most countries is the huge quantities of plastic waste, which has different types of polymers such as polyethylene terephthalate (PET), polypropylene (PP)., These plastics become a problem because of their non-biodegradability, toxicity, etc. The recovery of plastic waste in pavements has become an ecological technique that contributes to the preservation of natural resources.
In this study, PET waste was used as an additive for hot mix asphalt at two sizes (2.50 to 1.25 mm, and 0.315 to 0.160 mm) and three contents (3%, 5%, and 7% by weight of binder), PET modified mixes creep-recovery behavior was tested by four points bending test and compared with control mix (without PET waste) at three different temperatures (0°, 25° and 50° C), were added directly to the mixture as the method of dry process.
The results showed that the addition of PET waste yields better results that which could increase the asphalt bituminous resistance against permanent deformation and a clear rigidity improvement in the various temperature because it's more thermally stable and can limit the degradation risks of the bituminous mixtures compared to the control mixture. Further, can be prepared an eco-friendly road construction with less material cost
Mesoscale investigation of mass concrete temperature control systems and their consequences on concrete mechanical behaviour.
Get PDFThis study investigates the impact of aggregate and pipe cooling systems on concrete behaviour at a mesoscale level. Firstly, a Chemo-Thermo-Mechanical model is developed to investigate the initial stress state of early age hydration concrete followed by a mechanical analysis of the consequences brought by this initial state. Pipe and aggregate cooled concrete samples have been subjected to tensile and cyclic loadings. The results have been discussed in terms of damage and crack openings. It has been concluded that early age hydration modifies the initial conditions of any concrete structures. Regarding the cyclic behaviour, initial state due to the hydration process leads to permanent displacements corresponding to damage and cracking. The cooling methods improve the mechanical behaviour of concrete
Mechanical Behaviour and Fractured Surface Analysis of Bauxite Residue and Graphite Reinforced Aluminium Hybrid Composites
Get PDFComposite materials application areas have gradually grown, allowing them to reach and conquer new markets from consumer products to specialized niche applications, advanced composite materials make up a significant portion of the engineered materials industry. The purpose of this study is to investigate the mechanical properties of Aluminum (Al), Red Mud particle (RMp), Graphite particle (GRp) hybrid composites. The different combinations of Rm and Gr wt. % were used to prepare Al-Rm-Gr and Al-Gr-Rm hybrid composites. The mechanical properties namely Ultimate tensile strength, Compressive strength and Hardness of prepared hybrid composites are tested to know the influence of reinforcements in Al-8011 alloy. Synthesis of Aluminum-Red Mud-Graphite hybrid composites done by Stir casting method. Drastic reduction in grain size (Grain refinement) was observed in Scanning Electron Microscopic images of fractured surfaces of the tensile specimens, with addition of RMp and GRp to the matrix alloy thus soft alloy is turned into hard and brittle material. Among all the compositions of hybrid composites series AG8R10 was observed to be higher compressive strength and hardness while AR8G10 has higher ultimate tensile strength
The proposition of analytical expression HM–(√P/S) in microindentation pile-up deformation mode
Get PDFIn this article, the characteristic curves of microindentation measured on Cu99 were analyzed on the basis of the analytical expression proposed by Habibi et al. (J. Mater. Res, 2021, 36 (15): 3074-3085). It was found that the ratio of the applied load to the square of the displacement, P/(h+h0)2, does not remain constant during the loading segment of the microindentation test. An empirical expression for the determination of Martens hardness as a function of indentation load, contact stiffness and reduced modulus of elasticity by analyzing indentation load curves has been proposed for pile-up mode strain with the corrections imposed by the tip defect, the compliance of the instrument and the axial axisymmetry coefficient of the Vickers indenter. The results from microindentation tests on this examined ductile material show excellent agreement
Experimental behavior based on effective slab width acting as a flange with supporting steel beams in composite floors with openings
Get PDFAn experimental study with many variables was carried out to investigate the effective width of simply supported composite beams (T&L sec. beams) with & without slab opening. Three full-scale composite slab models with six different carrier simply supported composite beams (three with T-sec. & three with L-sec.) with constant slab rectangularity was tested. Each model loaded by uniform load (in the elastic zone) then loaded by means of two-concentrated load system acting at equal distances from supports till failure. One of them without slab opening and the others with two symmetric slab openings and constant opening horizontal position.
All standard tests were performed and all instructions and precautions were followed as perfect as the laboratory instruments permitted. All experimental steps were executed in a manner such that meeting practical conditions as exactly as could. In this research, the tested model features, materials properties and measurement instrumentations are described in brief. The maximum load carrying capacity; crack patterns, generated strains and deflections at different positions were experimentally investigated. For the sake of analysis generalization and error minimization, all results were analyzed by means of dimensionless relations. The results were recorded and analyzed guided by their mechanical behavior. Interesting gained results, conclusions and recommendations are introduced
Numerical analysis of bonded composite patch efficiency in the case of lateral U and V-notched aluminium panels
Get PDFIn this study, the finite element method is applied to investigate the mechanical behavior of aluminium notched structures reinforced by composite patch. In order to evaluate the efficiency of patches in the case of lateral semicircular and V-notches, it is very important to analyze the stress distribution at the notch tip and to take in consideration the influence of the geometrical and mechanical properties of the patch and the adhesive. Simple and double patch were used as reinforcement techniques. Results showed that the stress concentration factor is reduced at the notch tip by using a double patch reinforcement. This reduction becomes more noticeable when the patch thickness increases
Statistical evaluation of the effect of hygrothermal aging on the interlaminar shear of GFRP
Get PDFИзучение закономерностей изменения свойств, накопления повреждений и разрушения конструкционных композитов после гигротермического старения представляет собой актуальное и важное направление. В работе представлены результаты механических испытаний на межслойный сдвиг образцов электротехнического конструкционного стеклопластика и эпоксидного композита до и после предварительного гигротермического старения в рабочих средах (техническая вода, морская вода, машинное масло) различной продолжительности (15, 30 и 45 суток. ) и различных температур (22, 60 и 90ºС). Результаты испытаний были использованы для статистической оценки значимости немонотонных изменений прочности в случае межслойного сдвига после предварительного гигротермического старения относительно номинального материала с использованием ANCOVA и регрессионного анализа. Такие методы показали, что морские и технологические водные растворы отрицательно влияют на прочность на межслойный сдвиг, но их влияние было немного различным и сильно зависело от эффекта взаимодействия между временем воздействия и температурой раствора. Таким образом, максимальная разница составляет около 15% и 12% после 45 дней внутри технологической и морской воды при температуре 90 ºC соответственно. Напротив, воздействие машинного масла привело к увеличению прочности, но эффект более слабый по сравнению с водными растворами (около 6%)
Detection of Uniaxial Fatigue Stress under Magnetic Flux Leakage Signals using Morlet Wavelet
Get PDFThis paper demonstrates the application of continuous wavelet transform technique for magnetic flux leakage signal generated during a uniaxial fatigue test. This is a consideration as the magnetic signal is weak and susceptible to being influenced by an external magnetic field. The magnetic flux leakage signal response of API steel grade X65 is determined using Metal Magnetic Memory under cyclic load conditions ranging from 50% to 85% of the UTS. To facilitate further signal analysis, the magnetic flux gradient, the dH(y)/dx signal were converted from a length base into time series in this study. Magnetic flux leakage readings indicated a maximum UTS load of 56.5 (A/m)/mm at 85%, where a higher load resulted in a higher reading and the signal contained Morlet wavelet coefficient energy of 1.02×106 µe2/Hz. As increasing percentages of UTS loads were applied, the signal analysis revealed an increasing linear trend in the dH(y)/dx and wavelet coefficient energy. The analysis revealed a strong correlation between the wavelet coefficient energy and the dH(y)/dx amplitude, as indicated by the coefficient of determination (R2) value of 0.8572. Hence, this technique can provide critical information about magnetic flux leakage signals that can be used to detect high stress concentration zones