Cyclic Bending Loads Research Articles

Experimental and numerical study of circular columns reinforced with steel and glass FRP bars

Fibre-reinforced polymer (FRP) bars are important replacements for reinforcements made of ordinary steel because the former offer structural durability, electromagnetic neutrality and a high strength/weight ratio, as well as being lightweight and flexible. In the present study, six concrete columns with a diameter of 29·7 cm, a height of 1·5 m but with different percentages of steel and glass FRP bars were tested for endurance under a combination of an axial load and a reversed cyclic bending load up to failure. The experimental and numerical results in terms of force–displacement hysteresis are presented and discussed in this paper. Theoretical analysis was devoted to the refined modelling of the complex hysteretic response of experimentally tested columns with ordinary and composite reinforcement. Finite-element models of the specimens were formulated using a modelling concept of refined fibre sections.

Patterned Metal/Polymer Strain Sensor with Good Flexibility, Mechanical Stability and Repeatability for Human Motion Detection.

Wearable health monitoring smart systems based on flexible metal films are considered to be the next generation of devices for remote medical practice. However, cracks on the metallic surface of the films and difficulty in repeatability are the key issues that restrict the application of such wearable strain sensors. In this work, a flexible wearable strain sensor with high sensitivity and good repeatability was fabricated based on a patterned metal/polymer composite material fabricated through nanoimprint lithography. The mechanical properties were measured through cyclic tension and bending loading. The sensor exhibited a small ΔR/R0 error line for multiple test pieces, indicating the good mechanical stability and repeatability of the fabricated device. Moreover, the sensor possesses high sensitivity with gauge factors of 10 for strain less than 50% and 40 for strain from 50% to 70%. Various activities were successfully detected in real-time, such as swallowing, closing/opening of the mouth, and multi-angle bending of elbow, which illustrates the proposed sensor’s potential as a wearable device for the human body.

Fatigue strength of cruciform joints and longitudinal joints with laser-arc hybrid welding

This study examined the fatigue strength of cruciform joints and longitudinal joints fabricated with laser-arc hybrid welding. Load-carrying and non-load-carrying cruciform welded joints with plate thicknesses of 8, 16, and 25 mm were tested under tensile cyclic loads and out-of-plane bending cyclic loads. In longitudinal joints, four-point bending fatigue tests were performed on plate girders with flanges and a web connected by laser-arc hybrid welding. When assembling the plate girder, tack welds were installed at the flange-to-web connection to clarify their effect on the fatigue strength of the longitudinal joints. Measurements of weld toe profiles and residual stress were also conducted. The residual stress was measured using X-ray diffraction. The test results revealed that the fatigue strengths of hybrid welded joints are equivalent to those of arc welded joints and satisfy the fatigue design curves specified by the Japanese Society of Steel Construction. In addition, the effect of plate thickness on the fatigue strength was observed in hybrid welded joints as well as in arc welded joints.

Fatigue strength of laser-arc hybrid welded joints with tack welds

ABSTRACT This study examined the fatigue strength of cruciform joints and longitudinal joints fabricated with laser-arc hybrid welding, in which tack welds were installed at the connection. The cruciform joints were tested under tensile cyclic loads and out-of-plane bending cyclic loads. In the longitudinal joints, four-point bending fatigue tests were performed on plate girders fabricated with the hybrid welding. In addition, finite element analysis was performed on the cruciform joint to investigate the effect of tack welds on stress concentration at weld toes. The test results revealed that the fatigue strengths of the hybrid welded joints are equivalent to those of arc welded joints with or without tack welds and satisfy the fatigue design curves specified in JSSC recommendation. Moreover, the analysis results indicated that tack welds have little influence on stress concentration at weld toes in cruciform joints fabricated with laser-arc hybrid welding.

Enhanced Fatigue Behavior in Quenched and Tempered High-Strength Steel by Means of Double Surface Treatments

The aim of this study is to maximize the fatigue life of a high-strength steel. For this purpose, two different kinds of double surface treatments were studied: shot peening plus vibratory finishing and shot peening plus grit blasting. First, a high-intensity peening treatment was applied, with the aim of inducing a deep region submitted to high compressive residual stresses, and a second surface treatment was followed, to reduce the roughness induced in the first treatment and mitigate the damage produced on the specimen surface. The use of such double treatments was demonstrated to be a good choice to achieve high surface hardening and deep compressive residual stress profiles and to minimize surface defects. The fatigue life of the steel was greatly enhanced following the application of both double surface treatments. A vibratory treatment applied for 24 h after the application of a previous shot peening treatment was able to increase the average fatigue life of the single shot-peened samples almost sevenfold, but a much greater fatigue enhancement was produced using grit blasting for only 60 s. Anyway, both second treatments are able to remove the damaged surface layer produced in the first high-intensity shot peening treatment. The obtained results also revealed that an appropriate combination of surface treatments (shot peening + secondary treatment) avoided the initiation of cracks at the surface of the specimens under cyclic bending loads. Instead, crack initiation took place beneath the compressive residual stress field, induced in alumina inclusions that acted as stress concentrators.

Experimental Study and Analytical Modeling on Fatigue Properties of Pervious Concrete Made with Natural and Recycled Aggregates

As a solid pollutant, the recycled aggregate can be reused to replace the natural aggregate to cast pervious concrete, promoting resource recycling and reducing environmental pollution. Pervious concrete is usually applied to transportation engineering as pavements and decks, which are often subjected to fatigue loads in service. Therefore, it is essential to investigate the fatigue mechanical properties of pervious concrete. In this study, four-point cyclic bending loading test of natural aggregate pervious concrete and recycled aggregate pervious concrete were conducted under four different stress levels. By analyzing the experimental results, the mechanical performances, including hysteresis curve characteristics, damping ratio, dynamic elastic modulus and cyclic strain, of two kinds of pervious concrete under cyclic loading were revealed. Based on the improved EPF model, the relationship between fracture parameters, plastic strain and unloading strain were obtained. Besides, the relationship between the loading cycles and the ratio of plastic strain to unloading strain was received according to fatigue testing data under different stress levels. Further, the simplified fatigue model of pervious concrete was proposed and the experimental data was fitted with the model results. The fitting result reached a good agreement.

Ratcheting boundary of pressurized pipe under reversed bending

Ratcheting boundary is firstly determined by experiment, elastic-plastic finite element analysis combined with C-TDF and linear matching method, which is compared with ASME/KTA and RCC-MR. Moreover, based on elastic modulus adjustment procedure, a novel method is proposed to predict the ratcheting boundary for a pressurized pipe subjected to constant internal pressure and cyclic bending loading. Comparison of ratcheting boundary of elbow pipe determined by the proposed method, elastic-plastic finite element analysis combined with C-TDF and linear matching method, which indicates that the predicted results of the proposed method are in well agreement with those of linear matching method.

Experimentally and Numerically Analyzed Piezoelectric Characteristics of PZT Ceramics

The electric generation characteristics of the PZT piezoelectric ceramics were examined experimentally and numerically. In this case, cyclic bending loading was applied to the PZT ceramics: bulk and thin-film membrane. Electric voltage increased with increasing the strain value. There was a sharp initial increase in positive voltage for the PZT ceramics as bending load was applied. Following this initial increase stage, a rapid fall to zero occurred. The reduction rate of the positive voltage was changed depending on the rigidly of the PZT ceramic: the higher the reduction rate, the higher the rigid of the ceramic. The electrical voltage from the circular membrane PZT ceramic during cyclic loading showed the higher level compared to that for the bulk one, in which the flexibility of the PZT ceramic was significant factor to obtain the high electric voltage. The variation of the electric voltages was estimated numerically, which was relatively in good agreement with the experimental one.

Comparative Approaches for Fatigue Life Estimation of Aluminium Alloy for Aerospace Applications

The objective of this paper is to estimate the fatigue life behaviour of Al 7075-T6 using experimental and numerical methods for the purpose of aerospace applications. In this paper, initially static properties for the specimens are determined using Universal Testing Machine (UTM) under tensile loading. The cyclic bending load is applied on the material using fatigue test and the dynamic properties are determined. Experimental and numerical studies are carried out to determine the fatigue strength and endurance limit values of aluminium alloy 7075-T6 at different types of loading. The fatigue strength and structural integrity of the aluminium alloy 7075 - T6 are investigated using S-N curve. In numerical simulation, the reference model of this paper has been modelled by CATIA and thereby it is imported into ANSYS workbench 16.2 to investigate the stress distribution and number of cycles to failure of an aluminium alloy 7075-T6 under tensile loading. The mechanical properties are evaluated using both the approaches and finally the comparative study is carried out.

Fatigue crack propagation behaviour of RC beams strengthened with prestressed CFRP under cyclic bending loads

AbstractNumerical and experimental methods were applied to investigate the fatigue crack propagation behaviour of the reinforced concrete (RC) beams strengthened with prestressed carbon fibre laminate (CFL). On the one hand, a theoretical analysis method was presented to calculate the stress intensity factor K of the main crack on RC beam strengthened with prestressed CFL. On the other hand, fatigue crack propagation tests were carried out to obtain the crack propagation rate on RC beams strengthened with CFL, which had different prestressing levels (0%, 15%, and 22%). For accurate description of the fatigue crack propagation and fatigue life prediction, the digital image correlation method was used to capture the fatigue crack pattern. Based on the numerical and experimental method, a modified version of Paris' law was proposed. Compared with RC beams strengthened with nonprestressed CFL, the main crack propagation rates on RC beams strengthened with prestressed CFL having prestressing levels of 15% and 22% were decreased by 28% and 33%, respectively. The effectiveness of the proposed modified version of Paris' law was verified.

Mechanical Behavior of Dented Steel Pipes Subjected to Bending and Pressure Loading

The presence of dents on steel pipeline wall may constitute a threat for pipeline structural safety. Experimental testing results supported by numerical simulations are reported, in an attempt to assess the structural integrity of smoothly dented (nongauged) steel pipes. Ten experiments on 6 in diameter X52 steel pipes are reported, where dented steel pipes are subjected to bending and pressure loading, in order to estimate their residual strength and remaining fatigue life. Six specimens were subjected to cyclic bending loading, whereas four dented pipe specimens, following cyclic pressure loading, have been pressurized to burst to determine their ultimate pressure capacity. Numerical simulation of the testing procedure and, in particular, the loading pattern of each specimen (denting and cyclic loading) has also been performed so that local stress and strain distributions at the dented region are calculated accurately. Based on the finite element results, a simple and efficient fatigue assessment methodology is adopted, to estimate the remaining fatigue life and the predictions were found to compare with the experimental results. Finally, following a parametric numerical study, strain concentration factors (SNCFs) for dented pipes subjected to bending are calculated, to be used in fatigue life assessment.

J-integral approach for main crack propagation of RC beams strengthened with prestressed CFRP under cyclic bending load

Compared to the passive bonding strengthening technique using carbon fiber reinforced polymer (CFRP) for reinforced concrete (RC) structures, an active strengthening technique with prestressed FRP for reinforcing RC bridge structures with crack-like defects can make the stress distribution more reasonable, and can inhibit crack propagation. In this study, experimental and numerical methods were applied to investigate the fatigue crack propagation behavior of RC beams strengthened with prestressed carbon fiber laminate (CFL). Fatigue crack propagation tests were carried out to obtain the crack propagation rate on RC beams strengthened with CFL, which had different prestressing levels (0%, 15%, and 22%). The digital image correlation (DIC) method was used to capture the fatigue crack pattern. The finite element method was applied to calculate the J-integral of the main crack on RC beams strengthened with prestressed CFL. For accurate description of the fatigue crack propagation and fatigue life prediction, fatigue crack propagation tests were conducted. Based on a theoretical derivation, a modified version of Paris’ law was proposed. Compared to RC beams strengthened with non-prestressed CFL, the main crack propagation rates on RC beams strengthened with prestressed CFL having prestressing levels of 15% and 22% were decreased by 38.6% and 43.0%, respectively. Higher prestressing levels contribute to a greater resistance to crack propagation.

Effect of sulphate attack on the flexural fatigue behaviour of fly ash–based geopolymer concrete

In this work, the erosion effect of sulphate solution on the flexural fatigue behaviour of fly ash–based geopolymer concrete was investigated. Under cyclic bending loading, the effect of sulphate attack on the fatigue life of geopolymer concrete was analysed using the static flexural strength as the damage index. Results revealed that the fatigue life of geopolymer concrete after sulphate erosion was significantly reduced compared with uncorroded samples under the same fatigue loading condition. And the fatigue life of corroded/uncorroded geopolymer concrete can be approximately described by the two-parameter Weibull distribution model. Since the sulphate attack would increase the actual stress level of corroded geopolymer concrete, a fatigue equation considering the damage index was deduced to predict the fatigue life of geopolymer concrete after sulphate attack.

Surface Crack Propagation Rules of CFL-Strengthened Steel Plate under Fatigue Loading

Steel is a kind of common materials in construction. Surface crack in steel components can reduce the bearing capacity and durability of steel structures, so it is important to strengthen the steel components with crack defects. Strengthening with fiber reinforced polymer (FRP) is a reliable reinforcement method to improve structural mechanics properties. This paper presents an experimental study on surface crack propagation rules. Carbon fiber laminate (CFL) is adopted to strengthen X80 steel plate with a semi-elliptical surface pre-crack. Specimens are tested under cyclic bending load and fatigue lives, crack lengths and depths in various stages, and crack propagation rates are discussed.

Effect of cyclic bend loading on a cobalt-chromium clasp fabricated by direct metal laser sintering

Statement of problemLimited information is available regarding the mechanical properties of a partial removable dental prosthesis clasp fabricated by direct metal laser sintering (DMLS). PurposeThe purpose of this in vitro study was to measure the mechanical properties of cast clasps, DMLS clasps, and annealed DMLS clasps and to determine the correlation between cyclic bend loading, annealing, and mechanical properties. Material and methodsSixty half round clasp specimens were fabricated, with a length of 20 mm and a diameter of 1.5 mm at 10 mm from the tip. The specimens were divided into 6 groups (n=10). Twenty specimens were fabricated by casting (CS, CSAC), and 40 specimens were fabricated by DMLS (DS, DSAC, ADS, ADSAC). Of the DMLS specimens, 20 underwent annealing (ADS, ADSAC). Equivalent to 5 years of clinical use, 0.25 mm of bending was applied to group CSAC, DSAC, and ADSAC 14 600 times. After cyclic bending loads, a cantilever bend test was conducted on all groups, and the loads were measured. To compare the load values, 1-way ANOVA and the Tukey HSD test were performed and statistical significance among the groups was evaluated (α=.05). Scanning electron microscopy and energy-dispersive spectroscopy analyses were also used for surface morphology evaluation and element analysis. ResultsBending loads of the DMLS specimens were significantly lower than those of the cast specimens (P<.05). The influence of cyclic bending loads was significant for cast specimens (P<.05), but not for DMLS specimens (P>.05), in terms of variation of loads. Annealed DMLS specimens had significantly higher bending loads than DMLS specimens (P<.05). ConclusionsThe DMLS specimens had lower load values at 0.25 mm bending than cast specimens. The DMLS specimens were less influenced by cyclic bending loads than the cast specimens. Annealing increased load values of the DMLS specimens at 0.25 mm bending.

Cyclic loading of model silicone elastomer samples with regard to the failure of silicone breast implants

It is estimated that 15.000 to 20.000 breast augmentations are performed annually in Germany and several million worldwide. To obtain better knowledge of the reason for and the time of a possible failure of the implant shell, it is important to acquire information regarding the stability and durability of the material used and the associated failure criteria. The mechanical properties of silicone elastomers have, therefore, been investigated with regard to breast implants. Sample strips of the elastomer of various thicknesses were prepared and exposed to a cyclic bending load for a number of load cycles. Tensile specimens were punched out according to a defined pattern from the preloaded sample strips and tested with regard to their tensile properties, particularly the influence of cyclic loading on the stress at break. However, as quality of a silicone implant depends, not only on the strength of the material, but also on the spatial variation in the mechanical properties the quality of the silicone samples was also assessed in terms of the characteristic stress at break and the Weibull modulus, applying Weibull statistics to the tensile test results. The study revealed that the characteristic stress at break remained constant with increasing number of load cycles, but that the Weibull modulus decreased exponentially during the first 10.000 cycles to a critical level.

Fatigue Performance of SFPSC under Hot‐Wet Environments and Cyclic Bending Loads

A new structural material named “steel fiber polymer structural concrete (SFPSC)” with features of both high strength and high toughness was developed by this research group and applied to the bridge superstructures in the hot‐wet environments. In order to investigate the fatigue performance and durability of SFPSC under hot‐wet environments, the environment and fatigue load uncoupling method and the coupling action of environment and fatigue load were used or developed. Three‐point bending fatigue experiments with uncoupling action of environments and cyclic loads were carried out for SFPSC specimens which were pretreated under hot‐wet environments, and the experiments with the coupling action of environments and cyclic loads for SFPSC specimens were carried out under hot‐wet environments. Then, the effects of hot‐wet environments and the experimental methods on the fatigue mechanism of SFPSC material were discussed, and the environmental fatigue equations of SFPSC material under coupling and uncoupling action of hot‐wet environments and cyclic bending loads were established. The research results show that the fatigue limits of SFPSC under the coupling action of the environments and cyclic loads were lower about 15%. The proposed fatigue equations could be used to estimate the fatigue lives and fatigue limits of SFPSC material.

The influence of the structure on the fatigue properties of aluminium alloys for the casting

The article will be focused on monitoring the influence of the structure on the fatigue properties of Al-Mg cast alloy. As an experimental material were used aluminium alloys EN AC 51200 and EN AC 51500, supplied in a cast state without a heat treatment, which were produced by the continuous casting method. These alloys were selected on the basis of the chemical composition, where the content of most alloying elements is comparable. Fatigue properties of aluminium alloys were tested by three-point bending cyclic loading. The fracture surface of the testing sample was examined using scanning electron microscopy (SEM), where samples were observed on various stages of the fatigue process, their characteristics and differences of fracture surfaces.

The Structure of the Aluminium Alloy and Its Influence on the Fatigue Properties

The article will be focused on monitoring the influence of the structure on the fatigue properties of aluminium alloys for the casting of type Al-Mg, especially EN AC 51200 and EN AC 51500. These alloys were selected on the basis of the chemical composition, where the content of most alloying elements is comparable, only in the case of the concentration of magnesium are these alloys significantly different. Fatigue properties of aluminium alloys were tested by three-point bending cyclic loading. The fracture surface of the testing sample was examined using scanning electron microscopy (SEM), where samples were observed on various stages of the fatigue process, their characteristics and differences of fracture surfaces.

The Influence of the Structure on the Fatigue Properties of Al-Mg Cast Alloy

AbstractThe article will be focused on monitoring the influence of the structure on the fatigue properties of aluminium alloys for the casting of type Al-Mg. As an experimental material were used aluminium alloys EN AC 51200 and EN AC 51500, supplied in a cast state without a heat treatment. They were produced by the continuous casting method. These alloys were selected on the basis of the chemical composition, where the content of most alloying elements is comparable, only in the case of the concentration of magnesium are these alloys significantly different. Fatigue properties of aluminium alloys were tested by three-point bending cyclic loading. The fracture surface of the testing sample was examined using scanning electron microscopy (SEM), where samples were observed on various stages of the fatigue process, their characteristics and differences of fracture surfaces.