scholarly journals Development of a Vibration Technique Based on Geometric Optimization for Fatigue Life Evaluation of Sandwich Composite Structures

2021 ◽  
Vol 12 (1) ◽  
pp. 16
Author(s):  
Marco Menegozzo ◽  
Frederick A. Just-Agosto ◽  
David Serrano Acevedo ◽  
Basir Shafiq ◽  
Andrés Cecchini ◽  
...  
Keyword(s):  
Fatigue Life ◽  
Composite Structures ◽  
Sandwich Panels ◽  
Cost Effective ◽  
Fatigue Tests ◽  
Geometric Optimization ◽  
Bending Test ◽  
Sandwich Composite ◽  
Vibration Technique ◽  
Stress Ratios

A major obstacle to obtaining cost-effective experimental data on the fatigue life of sandwich panels is the prohibitive amount of time and cost required to carry out millions of cycles. On the other hand, vibration techniques applied to sandwich geometries fail to match the stress patterns that are obtained from standard flexural fatigue tests. To overcome such limitations, a vibration-based fatigue technique is proposed, which entails the use of sandwich specimens whose geometries are optimized to reproduce the stress distribution observed during three point bend loading while vibrating at the first resonant frequency. The proposed vibration technique was experimentally validated. The results, compared with the average number of cycles to failure at different stress ratios obtained via the Three-Point Bending test, showed high levels of accuracy. The proposed method is robust and time effective and indicates the possibility of attaining fatigue lifetime prediction of a wide class of composite elements, such as sandwich panels.

Fatigue behavior of wood-fiber-based tri-axial engineered sandwich composite panels (ESCP)

Holzforschung ◽  
2016 ◽  
Vol 70 (6) ◽  
pp. 567-575 ◽  
Author(s):  
Jinghao Li ◽  
John F. Hunt ◽  
Shaoqin Gong ◽  
Zhiyong Cai
Keyword(s):  
Fatigue Life ◽  
Shear Zone ◽  
Wood Fiber ◽  
Fatigue Tests ◽  
Bending Test ◽  
Sandwich Composite ◽  
Composite Panels ◽  
Pure Bending ◽  
Non Linear ◽  
Number Of Cycles

Abstract The static and fatigue bending behavior of wood-fiber-based tri-axial engineered sandwich composite panels (ESCP) has been investigated by four-point bending tests. Fatigue panels and weakened panels (wESCP) with an initial interface defect were manufactured for the fatigue tests. Stress σ vs. number of cycles curves (S-N) were recorded under the different stress levels. The primary failure mode in the fatigue tests was observed in the shear zone (epoxy debonding), which was different from face failure in the pure bending zone for the static bending test. For residual bending (RB) test, epoxy debonding failure occurred between the pure bending zone and shear zone. Macro cracks along the core/face interface developed as the number of cycles increased during the fatigue life. The crack propagation or damage for the panels submitted to fatigue test can be described as a three-stage damage process of first non-linear portion, followed by linear damage accumulation, and lastly non-linear accelerated damage. Bending stiffness degradation at the higher load level had faster degradation during fatigue life. The dissipated energy of the panels was small due to the high stiffness of the materials.

The Effects of Periodic High Loads on Fretting Fatigue

1981 ◽  
Vol 103 (3) ◽  
pp. 223-228 ◽  
Author(s):  
A. Kantimathi ◽  
J. A. Alic
Keyword(s):  
Aluminum Alloy ◽  
Fatigue Life ◽  
Growth Retardation ◽  
Fretting Fatigue ◽  
Fatigue Tests ◽  
Constant Amplitude ◽  
Axial Loads ◽  
Prolonged Fatigue ◽  
Stress Ratios ◽  
Crack Growth Retardation

Fretting fatigue tests have been conducted on 7075-T7351 aluminum alloy coupons with fretting pads of the same material. Three different stress ratios were used, the otherwise constant amplitude axial loads being interrupted every 1000 cycles by either tensile overloads to 400 MPa or compressive underloads to −200 MPa. Tensile overloads greatly prolonged fatigue life for low stresses where the overload ratios were 1.6 and above; compressive underloads had comparatively little effect. The results are discussed in terms of crack growth retardation phenomena.

Fabrication, characterization and mechanical testing of carbon fiber sandwich composites with nanoparticle included polyurethane adhesives

2021 ◽  
pp. 002199832110588
Author(s):  
Mehmet Emin Çetin
Keyword(s):  
Carbon Fiber ◽  
Composite Structures ◽  
Bending Strength ◽  
Mechanical Performance ◽  
Synergistic Effects ◽  
Sandwich Panels ◽  
Sandwich Composite ◽  
Scanning Calorimetry ◽  
Aluminum Honeycomb ◽  
Out Of Autoclave

In honeycomb core and composite face sheet sandwich panels, it is essential to understand the bonding characteristics of adhesive in relevance with its properties to observe synergistic effects of reinforcing nanoparticles such as multi-walled carbon nanotubes (MWCNTs). This study investigates the effects of MWCNT inclusion on polyurethane (PU) adhesive, which directly affects sandwich structures' structural and mechanical performance. MWCNTs are added to PU adhesive up to 0.2%, and their RAMAN spectroscopic analysis, Fourier transform infrared spectroscopy (FT-IR), thermo-gravimetric analyses (TGA) and differential-scanning calorimetry analyses (DSC) are evaluated. Aluminum honeycomb carbon-fiber-reinforced composite (CFRC) sandwich panels are fabricated using an out-of-autoclave manufacturing process. Carbon-fiber prepreg is used for top/bottom face sheets. Mechanical strength of face/core bonding evaluated as a function of MWCNT addition and core cell sizes. Manufactured sandwich composite structures are investigated for flat-wise tensile strength and three-point bending strength. Results show that MWCNT reinforcement to PU adhesive and lower cell size increases bending and flat-wise tensile resistances.

scholarly journals Design, Manufacturing, and Characterization of Hybrid Carbon/Hemp Sandwich Panels

2021 ◽  
Author(s):  
Luca Boccarusso ◽  
Fulvio Pinto ◽  
Stefano Cuomo ◽  
Dario De Fazio ◽  
Kostas Myronidis ◽  
...  
Keyword(s):  
Composite Structures ◽  
Failure Modes ◽  
Sandwich Panels ◽  
Industrial Applications ◽  
Low Velocity Impact ◽  
Sandwich Composite ◽  
Continuous Manufacturing ◽  
Low Velocity ◽  
Impact Compression

AbstractAdvanced sandwich composite structures that incorporate foams or honeycombs as core materials, have been extensively investigated and used in various applications. One of the major limitations of the conventional materials used is their weak impact resistance and their end-of-life recyclability and overall sustainability. This paper is focused on the study of the production and mechanical characterization of hybrid sandwich panels using hemp bi-grid cores that were manufactured with an ad hoc continuous manufacturing process. Bi-grid structures were stratified in multiple layers, resulting in cores with different thicknesses and planar density. Sandwich panels made with carbon fibers skins were then subjected to Low Velocity Impact, compression and indentation and the damaged panels were investigated via CT-Scan. Results show that the high tailorability of the failure modes and the very good energy absorption properties of the hybrid material open new exciting perspectives for the development of new sandwich structures that can extend the use of natural fibers into several industrial applications.

scholarly journals Static and Flexural Fatigue Behavior of GFRP Pultruded Rebars

Materials ◽  
2021 ◽  
Vol 14 (2) ◽  
pp. 297
Author(s):  
Michał Barcikowski ◽  
Grzegorz Lesiuk ◽  
Karol Czechowski ◽  
Szymon Duda
Keyword(s):  
Composite Materials ◽  
Composite Structures ◽  
Fatigue Behavior ◽  
Constant Load ◽  
Fatigue Tests ◽  
Bending Test ◽  
Radial Compression ◽  
Sinusoidal Waveform ◽  
Constant Load Amplitude ◽  
Steel Rebars

This paper presents the experimental results of composite rebars based on GFRP manufactured by a pultrusion system. The bending and radial compression strength of rods was determined. The elastic modulus of GFRP rebars is significantly lower than for steel rebars, while the static flexural properties are higher. The microstructure of the selected rebars was studied and discussed in light of the obtained results—failure processes such as the delamination and fibers fracture can be observed. The bending fatigue test was performed under a constant load amplitude sinusoidal waveform. All rebars were subjected to fatigue tests under the R = 0.1 condition. As a result, the S-N curve was obtained, and basic fatigue characteristics were determined. The fatigue mechanism of bar failure under bending was further analyzed using SEM microscopy. It is worth noting that the failure and fracture mechanism plays a crucial role as a material quality indicator in the manufacturing process. The main mechanism of failure under static and cyclic loading during the bending test is widely discussed in this paper. The results obtained from fatigue tests encourage further analysis. The diametral compression test reflects the weakest nature of the composite materials based on the interlaminar compressive strength. The proposed methodology allows us to invariantly describe the experimental transversal strength of the composite materials. Considering the expected durability of the structure, the failure mechanism is likely to significantly improve their fatigue behavior under the influence of cyclic bending. The reasonable direction of searching for reinforcements of composite structures should be the improvement of the bearing capacity of the outer layers. In comparison with steel rebars (fatigue tensile test), the obtained results for GFRP are comparable in the HCF regime. It is worth noting that in the near fatigue endurance regime (2–5 × 106 cycles) both rebars exhibit similar behavior.

scholarly journals Effect of Elevated Temperature on Bending Fatigue Behavior for Neat and Reinforced Polyamide 6,6

2020 ◽  
Vol 23 (3) ◽  
pp. 232-237
Author(s):  
Orhan Sabah Abdullah ◽  
Shaker S. Hassan ◽  
Ahmed N. Al-khazraji
Keyword(s):  
Fatigue Life ◽  
Elevated Temperatures ◽  
Fiber Composite ◽  
Fatigue Behavior ◽  
Fatigue Tests ◽  
Bending Test ◽  
Test Machine ◽  
Carbon Fiber Composite ◽  
Bending Fatigue ◽  
Different Temperatures

Recently, considering polymer composite in manufacturing of mechanical parts can be caused a fatigue failure due to the very long time of exposure to cyclic loading and may at environmental temperatures higher than their glass transition temperature; therefore, in this paper, a comprehensive investigation for bending fatigue behavior at room and elevated temperatures equal to 60 °C, 70°C, and 80 °C will be done. Rotating bending test machine was manufactured for this purpose supplied with a connected furnace to perform fatigue tests at elevated temperatures. The obtained results appeared that the increase in applied stress and temperature caused a clear reduction in fatigue life; also the addition of carbon nanotubes enhanced the fatigue life at different temperatures by 183%, 205%, 218%, and 240%, respectively while the addition of short carbon fibers improved fatigue life by 324%, 351%, 387%, and 415%, respectively. As well as, Polyamide 6,6/carbon fiber composite appeared fatigue limit at temperatures equal to 20°C and 60°C and stresses approximately equal to 55 MPa and 38 MPa respectively.

An Experimental Evaluation of High-Cycle Gear Tooth Bending Fatigue Lives Under Fully Reversed and Fully Released Loading Conditions With Application to Planetary Gear Sets

2020 ◽  
Vol 143 (2) ◽  
Author(s):  
Isaac J. Hong ◽  
Ahmet Kahraman ◽  
Neil Anderson
Keyword(s):  
Fatigue Life ◽  
Gear Tooth ◽  
Planetary Gear ◽  
Fatigue Tests ◽  
Experimental Methodology ◽  
Tooth Root ◽  
Loading Conditions ◽  
Bending Fatigue ◽  
Equivalent Number ◽  
Stress Ratios

Abstract High-cycle gear tooth bending fatigue lives of spur gears under fully reversed and fully released loading conditions are compared in this experimental study. The experimental methodology described in an earlier publication, (Hong et al. 2020, “A Rotating Gear Test Methodology for Evaluation of High-Cycle Tooth Bending Fatigue Lives Under Fully Reversed and Fully Released Loading Conditions,” Int. J. Fatigue, 133, p. 105432. 10.1016/j.ijfatigue.2019.105432), is employed to perform two sets of rotating, gear tooth bending fatigue tests. Statistical analyses are performed to regress stress versus life (S–N) curves under both loading conditions. These curves indicate that a gear under fully reversed loads has a shorter bending life at the same maximum tooth root stress as a gear under fully released loads. Various planetary gear set kinematic conditions with different stationary members are considered to determine the equivalent number of tooth loading cycles per revolution of the sun gear. They are combined with established S–N curves under both loading conditions to determine the ratios of allowable maximum tooth root stresses amongst the gear components of a P-planet gear set such that each gear in the set has the same bending fatigue life. A “stress-balanced” gear set designed to these stress ratios is expected to have the same bending fatigue life for its sun, ring, and planet gears, ensuring that the planetary gear set life is the longest.

Comparative fatigue properties estimation of composite structural nodes

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Miroslaw Rodzewicz
Keyword(s):  
Fatigue Life ◽  
Composite Structures ◽  
Evaluation Process ◽  
Fatigue Tests ◽  
Fatigue Properties ◽  
Composite Shells ◽  
Concentrated Force ◽  
Content Type ◽  
Structural Discontinuity ◽  
Strength Difference

Purpose The purpose of this paper is to present the concept of the author’s method of fatigue properties assessment of polymer composite structures, especially structures having nodes of concentrated force introduction (NCFI) using fatigue test data of coupons of similar composites and the ratio of their structural stress rate factors. Design/methodology/approach Basing on fatigue properties of pure composite shells coupons subjected to cyclic loads, and basing on the static strength difference between pure composite shells and shells having the structure affected by NCFI – (considered here as not only a manner of load introduction but also a kind of structural discontinuity), a method of relative fatigue properties reduction (RFPR) was developed. In the RFPR evaluation process, the author used the results of experiments on a special type of an NCFI named “a labyrinth non-adhesive node of concentrated force introduction” (LNA-NCFI) applied in certain composite gliders for fitting glider wings with the fuselage and also referred to design directives relating to primary structure of composite gliders, which are presented in the form of lightness factors linking stress with a structural mass. Findings The result of RFPR method application matched well with the results of fatigue tests of the LNA-NCFI type of a NCFI. The RFPR method may significantly facilitate the estimation of fatigue life of a structure with a structural discontinuity or an NCFI. Practical implications The RFPR method may significantly facilitate the estimation of fatigue life of a structure with a structural discontinuity or an NCFI. Originality/value The paper presents a proposal of a novel simplified method for fatigue life estimation of composite structures having a kind of structural discontinuity or an NCFI.

scholarly journals Fatigue Properties of Cold-Recycled Emulsified Asphalt Mixtures Fabricated by Different Compaction Methods

2019 ◽  
Vol 11 (12) ◽  
pp. 3483 ◽  
Author(s):  
Yingjun Jiang ◽  
Hongwei Lin ◽  
Zhanchuang Han ◽  
Changqing Deng
Keyword(s):  
Fatigue Life ◽  
Weibull Distribution ◽  
Vertical Vibration ◽  
Fatigue Tests ◽  
Asphalt Mixtures ◽  
Fatigue Properties ◽  
Tensile Fatigue ◽  
Cracking Performance ◽  
Stress Ratios ◽  
Emulsified Asphalt

This paper focuses on investigating the fatigue properties of cold-recycled emulsified asphalt mixtures (CEAMs) designed via two different compaction methods. First, two different CEAM compaction procedures were investigated and evaluated, including the modified Marshall compaction method (MMCM) and the vertical vibration testing method (VVTM). Indirect tensile fatigue tests were then performed to research the fatigue lives of CEAMs fabricated via the two methods. Finally, a Weibull distribution was applied to analyze the fatigue test results, and the fatigue equation was constructed. The results indicated that the average mechanical strength ratio between the CEAM samples produced by VVTM and the field core samples was >92%, whereas the average ratio of the specimens shaped by the MMCM was <65%. Compared with MMCM-molded CEAMs, VVTM-fabricated CEAMs showed decreased optimal moisture and emulsified asphalt contents by 11% and 9%, respectively, but exhibited improved moisture stability, anti-cracking performance, and anti-rutting performance by 4%, 12%, and 35%, respectively. The fatigue equations established on the basis of the Weibull distribution could effectively assess the fatigue life of CEAMs. The VVTM-manufactured CEAMs showed good resistance of stress change sensitivity and fatigue failure under different stress ratios. The VVTM-compacted CEAMs demonstrated increased fatigue life by 36% at a stress ratio of 0.45 and by 325% at a repeated load of 0.27 MPa compared with the MMCM-fabricated CEAMs.

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