scholarly journals Estimation of Notched Composite Plates Fatigue Life Using Residual Strength Model Calibrated by Step-Wise Tests

Materials ◽  
2018 ◽  
Vol 11 (11) ◽  
pp. 2180 ◽  
Author(s):  
Paweł Romanowicz ◽  
Aleksander Muc
Keyword(s):  
Fatigue Life ◽  
Residual Strength ◽  
Stress Ratio ◽  
Composite Plates ◽  
Fatigue Tests ◽  
Strength Model ◽  
Damage Growth ◽  
Testing Frequency ◽  
Fatigue Model ◽  
Layer Orientation

The proposed new technique of fatigue life prediction for notched composite plates is based on a residual strength model calibrated with the use of step-wise fatigue tests. It was proposed to calibrate the fatigue model with fatigue tests in which load conditions are in a step-wise fashion. The adopted fatigue model takes into account the most important loading parameters such as testing frequency, stress ratio, layer orientation and maximal fatigue stress. It was demonstrated that with the use of step-wise fatigue tests, it is possible to calibrate the fatigue model for a particular material and structure with the use of fewer samples. In the experimental tensile and fatigue tests TVR 380 M12/26%/R-glass/epoxy composite plates [+45°/−45°]4 with circular and elliptical cut-outs were used. The fatigue tests were performed under different loading conditions. The influence of testing frequency, stress ratio, maximal fatigue load and also geometry of the cut-out on damage growth rate and fatigue life were studied. The predicted fatigue life was in good agreement with the durability determined experimentally in all investigated samples.

Enhanced Portland Cement Concrete Fatigue Model for StreetPave

2005 ◽  
Vol 1919 (1) ◽  
pp. 29-37 ◽  
Author(s):  
Leslie Titus-Glover ◽  
Jagannath Mallela ◽  
Michael I. Darter ◽  
Gerald Voigt ◽  
Steve Waalkes
Keyword(s):  
Portland Cement ◽  
Stress Ratio ◽  
Design Method ◽  
High Volume ◽  
Fatigue Tests ◽  
Slab Thickness ◽  
Portland Cement Concrete ◽  
Cement Concrete ◽  
Fatigue Model ◽  
Pavement Thickness

The Portland Cement Association (PCA) pavement thickness design method for jointed concrete pavements is mechanistically based and consists of both fatigue and erosion analyses. It determines the minimum slab thickness required for a given set of site and design conditions on the basis of both fatigue and erosion criteria. At the heart of the fatigue analysis is the fatigue model, which establishes the number of allowable load repetitions for a given stress ratio [ratio of flexural edge stress caused by the application of wheel loads to the portland cement concrete (PCC) slab flexural strength]. The PCA fatigue model is based on data derived from beam fatigue tests conducted in the early 1950s and 1960s. The model estimates the conservative lower-bound estimate of the allowable number of load applications at a given stress ratio (i.e., it incorporates a high degree of reliability–-approximately 90% or higher). Although this may be desirable for high-volume, high-traffic pavements, it is too conservative for low-volume roads or street pavements. The PCA pavement thickness design method currently is being used in the American Concrete Pavement Association (ACPA) pavement design software, StreetPave. StreetPave incorporates the PCA's pavement thickness design methodology in a Windows-based user platform. ACPA commissioned a study to expand, improve, and broaden the current PCA fatigue model by including reliability as a parameter for predicting PCC fatigue damage and by calibrating the enhanced model with additional fatigue data from recently completed studies. An enhanced fatigue model was then developed.

scholarly journals Comparative Study on Fatigue Life of CFRP Composites with Damages

2019 ◽  
Vol 2019 (11) ◽  
pp. 28-38
Author(s):  
Marta Baran ◽  
Piotr Synaszko ◽  
Janusz Lisiecki ◽  
Sylwester Kłysz
Keyword(s):  
Residual Strength ◽  
Stress Ratio ◽  
Fatigue Tests ◽  
Equivalent Diameter ◽  
Compression After Impact ◽  
Strength Tests ◽  
Cfrp Composite ◽  
Sinusoidal Shape ◽  
Weight Impact ◽  
The Impact

AbstractIn this work, the compressive residual strength tests results, Compression After Impact (CAI), are presented. The specimens were made of carbon-epoxy prepreg E722-02 UHS 130-14. Two variants of specimens were tested: samples undamaged and samples with damage that was centrally introduced by a drop-weight impact, as per the ASTM D7136/7136M standard. An impactor with potential energy equal to 15J and the type of support required by the standard were used. The size of impacted damages, defined as an area of damage on a plane perpendicular to the impact direction, and the equivalent diameter were specified using the flash thermography method.The tests were performed using the fixtures manufactured according to the ASTM D7137/7137M standard. The specimens were compressed to determine the residual strength. This value was afterwards used to specify the force levels for the fatigue tests. The fatigue tests were carried out under force control – with a sinusoidal shape, stress ratio R equal to 0.1 and frequency f 1Hz. Maximum force in a loading cycle Pmax was being increased after each thousand of cycles N until its value was close to the residual strength determined in the previously mentioned tests. In this work, the following relationships were presented: force-displacement P-δ for both static and fatigue tests and displacement-loading cycles δ-N for fatigue tests.A method of conducting the fatigue tests of CFRP composite was proposed, in which both the CAI specimens and CAI fixture were used. This allowed researchers to accelerate making initial comparisons between the two groups of specimens with damages – grouped relative to the way of conditioning.

Fatigue Life Properties of Circumferentially-Notched Bar of Austenitic Stainless Steel With Various Concentration Factors

2018 ◽  
Author(s):  
Naoaki Nagaishi ◽  
Michio Yoshikawa ◽  
Saburo Okazaki ◽  
Hisao Matsunaga ◽  
Junichiro Yamabe ◽  
...  
Keyword(s):  
Stainless Steel ◽  
Fatigue Life ◽  
Stress Concentration ◽  
Austenitic Stainless Steel ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Stress Ratio ◽  
Ambient Air ◽  
Fatigue Tests ◽  
Concentration Factors

Fatigue tests were performed using three types of round-bar specimens of Type 304, meta-stable, austenitic stainless steel. The specimens had circumferential notch with stress concentration factors, Kt, of 2, 3 or 6.6. Load controlled fatigue tests were conducted at stress ratio, R, of 0.1 and −1 in ambient air at room temperature. At R of 0.1, fatigue life was decreased with an increase in the stress concentration factor. Conversely, at R of −1, the stress concentration factor had little influence on the fatigue life. To understand the mechanism of the stress ratio effect, local deformation behavior at and beneath the notch root during the fatigue test was computed by means of finite element analysis considering that the plastic constitutive model describes the cyclic stress-strain response.

Characteristics of Reliability-Dependent Hazard Rate for Composites Under Fatigue Loading

2009 ◽  
Vol 25 (2) ◽  
pp. 195-203 ◽  
Author(s):  
C. L. Chen ◽  
Y. T. Tsai ◽  
K. S. Wang
Keyword(s):  
Monte Carlo ◽  
Fatigue Life ◽  
Residual Strength ◽  
Hazard Rate ◽  
Fatigue Loading ◽  
Cyclic Stress ◽  
Rate Function ◽  
Strength Distribution ◽  
Hazard Rate Function ◽  
Strength Model

AbstractThis paper studies the characteristics of a proposed reliability-dependent hazard rate function for composites under fatigue loading. The hazard rate function, in terms of reliability R, is in the form of e+c (1-R)p called (ecp) model, where e denotes the imbedded defects of material strength, c the coefficient of strength degradation, and p the memory characteristics of distributions of both applied stress and fatigue strength during the cumulative damage process. By taking a typical residual strength model in Monte Carlo simulation, this paper presents the time changing of the residual strength distribution and hazard rate of composite under various constant-amplitude cyclic stresses. The values of (e, c, p) are decided by fitting hazard rate function to the data generated in simulation. The results show that, under a suitable suggested value of e, p is a constant depending on the characteristics of stress distribution as well as the residual strength model used in Monte Carlo stimulation, and c is correlated to the maximum cyclic stress in a power-law relationship. Only by knowing the initial strength distribution and the maximum cyclic stress, the fatigue life can be easily estimated by integrating the reliability with time or its equivalent, i.e., the reciprocal of hazard rate function with reliability. Finally, by a proposed approximated equation of fatigue life, the (ecp) model is checked to be highly consistent with S-N curve in both the physical means and the equation form. The analysis presented here may be helpful in designing and maintenance planning of composite under fatigue loading.

A Probabilistic Fatigue Model for Quasi-Brittle Materials

2014 ◽  
Vol 875-877 ◽  
pp. 1239-1242 ◽  
Author(s):  
Rena C. Yu ◽  
Luis Saucedo ◽  
Gonzalo Ruiz
Keyword(s):  
Stress Ratio ◽  
Brittle Materials ◽  
Initial Distribution ◽  
Fatigue Tests ◽  
Cumulative Distribution ◽  
Fatigue Model ◽  
Stress Ratios ◽  
Number Of Cycles ◽  
Cycles To Failure ◽  
Measured Strength

We aim to develop a new fatigue model valid for quasi-brittle materials like concrete, which properties have considerably larger standard deviation than metals. Having this in mind, we fit the measured strength data with a three-parameter Weibull cumulative distribution function and in turn take it as the initial distribution for an asymptotic fatigue model in concrete. We also take into account the observed influence of frequency and stress ratio on the fatigue life in concrete, both plain and reinforced with fibers. The developed model is validated against fatigue tests in compression on cubic specimens for different stress ratios and loading frequencies. The secondary strain rate is also found to be correlational with the number of cycles to failure.

scholarly journals Mechanical and Mesoscale Analyses of Cement Stabilized Macadam Prepared by Vibratory and Nonvibratory Mixing Techniques

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Jijing Wang ◽  
Zhihua Tan
Keyword(s):  
Fatigue Life ◽  
Stress Ratio ◽  
Cement Mortar ◽  
Stress Sensitivity ◽  
Fatigue Tests ◽  
X Ray ◽  
Loading Rates ◽  
Stress States ◽  
Mixing Techniques ◽  
Fatigue Equation

The objective of this study is to analyze the effects of mixing techniques on the mechanical behavior and meso-structure of cement-treated aggregate. Different specimens were prepared by vibratory and nonvibratory mixing techniques. X-ray CT scans were performed to illustrate the distribution of cement mortar on aggregate. The strength, modulus, and fatigue tests under different stress states were tested to reveal the impacts of mixing techniques. Then, the relationships between strengths and loading rates and that between moduli and stress levels were established. Hereafter, the S-N fatigue equation that modified with stress ratio related to loading rates was used to describe the fatigue performance. The results indicate that the cement mortar of specimens prepared by vibratory mixing was well-distributed on aggregates. The strength, modulus, and fatigue life of the specimens prepared by vibratory mixing were higher under the test condition threshold. Moreover, the growth rate of strength and modulus with loading for specimens prepared by vibratory mixing was slightly larger than that for specimens prepared by nonvibratory mixing. Compared with the cement-treated aggregates specimens prepared by nonvibratory mixing, the fatigue life of cement-treated aggregates specimens prepared by vibratory mixing had more stable stress sensitivity.

AN ANALYSIS OF MECHANICAL PROPERTIES OF ANODIZED ALUMINUM FILM AT HIGH STRESS

2015 ◽  
Vol 22 (01) ◽  
pp. 1550002
Author(s):  
XIXI ZHAO ◽  
GUOYING WEI ◽  
YUNDAN YU ◽  
YUEMEI GUO ◽  
AO ZHANG
Keyword(s):  
Fatigue Life ◽  
Fracture Surface ◽  
Stress Ratio ◽  
High Stress ◽  
Fatigue Tests ◽  
Aluminum Film ◽  
Anodic Films ◽  
Anodized Aluminum ◽  
Al 2024 ◽  
Cycles To Failure

In this paper, a new environmental-friendly electrolyte containing sulfuric acid and tartaric acid has been used as the substitute of chromic acid for anodization. The work discussed the influence of anodizing voltages on the fatigue life of anodized Al 2024-T3 by performing fatigue tests with 0.1 stress ratio (R) at 320 MPa. Meanwhile the fatigue cycles to failure, yield strength, tensile strength and fracture surface of anodic films at different conditions were investigated. The results showed that the fatigue life of anodized and sealed specimens reduced a lot compared to aluminum alloy, which can be attributed to the crack sites initiated at the oxide layer. The fracture surface analyses also revealed that the number of crack initiation sites enlarged with the increase of anodizing voltage.

scholarly journals Tensile Fatigue Behaviour of Polyester and Vinyl Ester Based Gfrp Laminates – a Comparative Evaluation

2020 ◽  
Author(s):  
Wahid Ferdous ◽  
Allan Manalo ◽  
Peng Yu ◽  
Choman Salih ◽  
Rajab Abousnina ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Failure Mode ◽  
Applied Stress ◽  
Environmental Conditions ◽  
Vinyl Ester ◽  
Stress Ratio ◽  
Fatigue Behaviour ◽  
Unique Contribution ◽  
Tensile Fatigue ◽  
Fatigue Model

Fatigue loading is critical to fibre reinforced polymer composites due to their anisotropic and heterogenous nature. This study investigated the tensile fatigue behaviour of polyester and vinyl ester based GFRP laminates to understand the critical aspects of failure mode and fatigue life under cyclic loading. GFRP laminates with two different resin systems (polyester and vinyl ester), two different stress ratios (0.1 and 0.5) and two different environmental conditions (air and water) were investigated at an applied stress of 80%, 60% and 40% of the ultimate capacity. Based on the investigated parameters (i.e., resin types, stress ratio, environmental conditioning and maximum applied stress), a fatigue model was proposed. Results show that the resin system plays a great role in fatigue failure mode while the stress ratio and environmental condition significantly affect the tensile fatigue life of GFRP laminates. The types of resin used in GFRP laminates and environmental conditions as input parameter in the proposed fatigue model is a unique contribution.

scholarly journals High-Temperature Low Cycle Fatigue Life Prediction and Experimental Research of Pre-Tightened Bolts

Metals ◽  
2018 ◽  
Vol 8 (10) ◽  
pp. 828 ◽  
Author(s):  
Qingmin Yu ◽  
Honglei Zhou ◽  
Xudong Yu ◽  
Xiangjin Yang
Keyword(s):  
High Temperature ◽  
Fatigue Life ◽  
Life Prediction ◽  
Low Cycle Fatigue ◽  
Equivalent Stress ◽  
Fatigue Tests ◽  
Fatigue Life Prediction ◽  
Cycle Fatigue ◽  
Stress Strain ◽  
Fatigue Model

Bolted connections are widely used in various mechanical structures due to their superior fastening properties. However, vibration and fatigue loads in the structure are likely to cause fatigue failure of the bolted joints, especially those under high temperature, such as in aero-engines. This paper mainly studies the low-cycle fatigue life of the pre-tightened bolts working at a high temperature. A novel test fixture is designed for fatigue tests, and low cycle fatigue tests of pre-tightened bolts are conducted at the temperatures of 550 °C and 650 °C, respectively. Furthermore, a new low cycle fatigue model that is based on the Von Mises equivalent stress/strain criterion is proposed. Meanwhile, the proposed model is used to predict the high-temperature low cycle fatigue life of pre-tightened bolts according to the stress/strain results obtained by finite element analysis. There is good agreement between the experimental results and those obtained by theoretical prediction, which validates the accuracy of the proposed fatigue model. Research results will provide a theoretical basis for the low cycle fatigue life prediction of pre-tightened bolts.

Residual properties of composite plates subjected to impact fatigue

2018 ◽  
Vol 53 (6) ◽  
pp. 799-817 ◽  
Author(s):  
Said Mouhoubi ◽  
Krimo Azouaoui
Keyword(s):  
Energy Level ◽  
Residual Strength ◽  
Damage Model ◽  
Composite Plates ◽  
Fatigue Tests ◽  
Multiple Impacts ◽  
Impact Fatigue ◽  
Residual Properties ◽  
Post Impact ◽  
Major Factors

This work deals with post-impact residual mechanical behavior of composite plates made with glass fiber cloth and two different thermosetting resins (epoxy and polyester). It is well known that damages induced by multiple impacts greatly reduce the residual properties. How are the residual strength or stiffness affected by the impacts? How does impact energy and number of impacts contribute to the degradation of mechanical properties? What kind of supports induces more damages and consequently a larger reduction in residual properties? These are some questions that we attempt to clarify in this paper. To investigate and assess the effect of the energy level and number of impacts on the total induced damage and residual properties, impact fatigue tests were carried out at selected energy range of: 3 J, 4 J, 5 J, and 6 J. Then, coupons containing the damaged area are cut out, in order to estimate the tensile, compressive, and shear residual properties, particularly residual strength. The energy level and number of impacts are major factors influencing the loss of stiffness and strength. However, stiffness is more affected than strength by the repeated impacts. A clear decrease of compressive residual strength with the number of impacts for the two fixture conditions (clamped on two opposite sides and a circular clamp) is demonstrated. The drop in the case of the circular clamping is more visible, confirming a greater extent of damages. A three-parameter damage model is proposed and applied, with some conclusions are withdrawn in this investigation.

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