Long-term Fatigue Performance Research Articles

Analysis of Chinese ancient brick masonry characteristics under uniaxial compression fatigue loading

Urban expansion and diversified traffic aggravate the damage and deterioration of ancient buildings. It is crucial to evaluate the long-term fatigue performance of ancient brick masonry structures for the safety and maintenance of ancient buildings. A series of indoor tests were conducted on the ancient brick masonry. The images for the whole process of the test were collected using VIC-3D technology. The relationship between the stress level and the number of failure cycles under compressive fatigue load and the stress–strain evolution under different stress levels were determined. A mathematical model of p-S-N fatigue life prediction based on probability was proposed, which comprehensively considered the maximum stress level, stress range, number of load cycles, and survival probability. The equivalent fatigue life of ancient brick masonry specimens under each failure probability obeys Weibull distribution, and then the fatigue life of masonry can be predicted at any expected confidence level. The test results provide reliable theoretical and data support for fatigue deterioration and life prediction of ancient masonry structures in service.

Ultrahigh cyclic stability and giant elastocaloric effect in directionally solidified (Ni50Mn28Fe2.5Ti19.5)99.4B0.6 alloy

Cyclic stability of elastocaloric materials is critically important for practical applications in solid-state refrigeration. Ni-Mn-based Heusler-type alloys exhibit a large elastocaloric response to low driving stress. However, these alloys can only be worked for short-term cyclic operation due to their intrinsic brittleness. Here, we demonstrate the achievement of giant elastocaloric effect (eCE) and long-term fatigue performance in a directional solidification (Ni50Mn28Fe2.5Ti19.5)99.4B0.6 alloy. At 303 K, the maximum compressive strength and strain of the alloy can be as high as 2734 MPa and 20.5%, respectively. During fast loading and unloading with the stress of 435 MPa and the strain of 8%, giant adiabatic temperature change (ΔTad) of 25.1 K and -24.5 K can be obtained, respectively. In particular, a large ΔTad of about 5.8 K is generated during cycling at 360 MPa stress and 3.5% strain, and can be maintained for more than 20,000 cycles.

Effect of air voids and asphalt content changes on laboratory and simulated long-term fatigue performance of asphalt concrete pavements

Effect of air voids and asphalt content changes on laboratory and simulated long-term fatigue performance of asphalt concrete pavements

Development of a Fatigue Damage Model for Roller Compacted Concrete Pavement Based on In Situ Saw-Cut Beams and Accelerated Pavement Performance

As a durable, economical, and low-maintenance concrete material, roller compacted concrete (RCC) is steadily becoming the preferred choice for many pavement applications. However, the fatigue models in current pavement thickness design procedures have generally been found to over-predict the RCC pavement fatigue damage under in situ heavy truck loading. In this study, a comprehensive beam fatigue test experiment was performed using field saw-cut RCC slab samples from two full-scale accelerated pavement testing (APT) sections to investigate the fatigue behavior of in situ RCC pavements. This is the first research study to investigate the fatigue behavior of field RCC beam samples prepared and constructed with a high-density asphalt-type paver and a vibratory roller. The results indicate that a well-compacted RCC pavement can achieve higher flexural strength and exhibit better fatigue life than conventional concrete pavement. Based on the beam fatigue test results and in situ fatigue performance of APT test sections, an RCC fatigue-life model was developed, providing a more accurate solution for estimating the allowable number of load repetitions of RCC pavements subjected to vehicular fatigue loading. This model could be used in RCC thickness design procedures to determine the optimum RCC design thickness and long-term fatigue performance of RCC pavements for roadway application.

Oversizing of self-expanding Nitinol vascular stents – A biomechanical investigation in the superficial femoral artery

Despite being commonly employed to treat peripheral artery disease, self-expanding Nitinol stents are still associated with relatively high incidence of failure in the mid- and long-term due to in-stent restenosis or fatigue fracture. The practice of stent oversizing is necessary to obtain suitable lumen gain and apposition to the vessel wall, though it is regarded as a potential cause of negative clinical outcomes when mis-sizing occurs. The objective of this study was to develop a computational model to provide a better understanding of the structural effects of stent sizing in a patient-specific scenario, considering oversizing ratio OS, defined as the stent nominal diameter to the average vessel diameter, between 1.0 and 1.8. It was found that OS < 1.2 resulted in problematic short-term outcomes, with poor lumen gain and significant strut malapposition. Oversizing ratios that were in the range 1.2 ≤ OS ≤ 1.4 provided the optimum biomechanical performance following implantation, with improved lumen gain, reduced incomplete stent apposition and favourable predicted long-term fatigue performance. Excessive oversizing, OS > 1.4, did not provide any further benefit in outcomes, showing limited increases in lumen gain and unfavourable long-term performance, with higher mean strain values predicted from the fatigue analysis. Therefore, our findings predict that the optimal oversizing ratio for self-expanding Nitinol stents is in the range of 1.2 ≤ OS ≤ 1.4, which is similar to clinical observations, with this study providing detailed insight into the biomechanical basis for this.

Original versus nonoriginal cast-to-gold abutment-implant connection: Analysis of the internal fit and long-term fatigue performance

Statement of problemRestoring implants with nonoriginal abutments is common. However, studies that evaluated compatible abutments with long-term fatigue performance are lacking. PurposeThe purpose of this in vitro study was to assess the internal fit and the cyclic fatigue life after artificial aging of 3 implant-abutment configurations restored with 1 original and 2 compatible nonoriginal cast-to-gold abutments. Material and methodsForty-eight original internal hexagon connection implants were connected to 3 different brands of abutments (n=16): 1 original to the implant system and the other 2 with nonoriginal abutments. Internal fit and the percentage of surface with tight contact were assessed by scanning electron microscopy in 12 cross-sectioned specimens (n=4) at 3 different areas (platform, internal, and screw). Thirty-six implant-abutment-crown specimens (n=12) were immersed in artificial saliva and thermocycled for 10 000 cycles between 5 °C and 55 °C. Subsequently, a cyclic load test, as per International Organization for Standardization (ISO) Standard 14 801, was completed in a universal testing machine at 2 Hz in air. ResultsThe original abutments presented the best fit and highest percentage of tight contact in the internal areas. In addition, the original abutments showed the lower cyclic fatigue strength degradation and the highest long-term success. ConclusionsOcclusal loads are transferred more homogenously through the system when original abutments are used because of the better fit between the internal components, leading to increased fatigue resistance.

Study on fatigue failure of glass fibre-reinforced thermoplastic pipe

The long-term fatigue performance of a glass fibre-reinforced thermoplastic pipe (RTP) is mainly determined by that of its glass fibre reinforcement layer. Glass fibre has an irregular network structure consisting of SiO4 tetrahedrons. In this network structure, there exists numerous defects. Under cyclic loading, cracks are initiated at these defects and grow steadily and perhaps even disruptively, ultimately leading to the fracture of the glass fibre. The mean stress corresponding to the occurrence of disruptive crack propagation is referred to as the critical fatigue stress. When the mean cyclic load is smaller than the critical value, the growing cracks stop propagating when in contact with high-energy chemical bonds. When the mean cyclic load is larger than the critical value, the glass fibre is doomed to fracture. In the present study, a series of fatigue tests was performed on a RTP subjected to cyclic loadings of different mean stresses. The numbers of cycles to failure at different mean stresses obtained from the tests were then used to estimate the critical fatigue stress of the RTP. The mechanism underlying the fatigue failure was analysed using fatigue mechanics and chemical bond theories.

Mechanistic analysis and cost-effectiveness evaluation of asphalt rubber mixtures

Traffic loading has been associated with different main distresses occurring in the pavements. Fatigue cracking and rutting can be considered as the main distresses occurring in the pavement structure. Studies conducted in the past have shown improved mechanical performance of asphalt rubber mixtures, but only few of these studies are inclined in investigating the long-term mechanistic performance and the cost-effectiveness of the addition of rubber into asphalt mixtures. A mechanistic analysis utilising 3D Move software package was performed to assess the long-term fatigue performance and rutting performance of two different mixtures, namely: conventional hot mixed asphalt (HMA) and asphalt rubber (AR). Two different pavement construction scenarios were investigated as a newly constructed pavement structure and a rehabilitated overlay. Each mixture was analysed for two different vehicle speeds and two different pavement thicknesses that totalled 16 different 3D Move mechanistic analysis scenarios (2 asphalt mixtures × 2 construction scenarios × 2 vehicle speeds × 2 pavement thicknesses). The maximum tensile strain at the bottom of the asphalt layer for each scenario was utilised to establish a fatigue ratio that compared AR to the corresponding conventional HMA pavement sections. In addition, a cost-effectiveness analysis was carried out for the same 16 scenarios. Overall, the mechanistic analysis showed that the fatigue life of an AR was six times greater than that of conventional HMA layer for a new construction, and for the overlay, AR had 40 times more fatigue life than a conventional HMA. The rutting life was also increased with the use of asphalt rubber. In the case of cost-effectiveness analysis, AR exhibited four times lower cost per 1000 fatigue life cycles and three times lower cost per cycle of rutting when compared to a conventional HMA in a new construction. For an overlay scenario, AR exhibited 23 times lower cost per 1000 fatigue life cycles and around four times lower cost per cycle of rutting compared to a conventional HMA overlay.

Fatigue performance of long-term aged crumb rubber modified bitumen containing warm-mix additives

Recently warm mix asphalt (WMA) technologies have been introduced to rubberized asphalt mixtures to decrease the required construction temperatures and to alleviate the hazardous gas emissions. Rubberized asphalt pavements combining with WMA have the potential to improve the long-term pavement performance. This study aims to investigate the fatigue performance of crumb rubber modified bitumen (CRMB) containing warm-mix additives using different characterization methods. The effects of crumb rubber modifier (CRM) content (5%, 10%, 15% and 22% by weight of base bitumen) and warm-mix additives on the binder fatigue performance were investigated. Various laboratory tests, including frequency sweep tests, time sweep (TS) tests and linear amplitude sweep (LAS) tests, were conducted on the long-term aged binders to obtain indicators of fatigue performance. Results show that there is a good correlation between the measured fatigue life determined by TS tests using the dissipated energy concept and the predicted fatigue life determined by LAS tests using the simplified viscoelastic continuum damage (S-VECD) theory. However, the traditional Superpave fatigue parameter and the G-R parameter cannot characterize accurate enough the fatigue performance of modified binders. CRMB binders exhibit superior fatigue performance compared to the neat bitumen. The effects of warm-mix additives on the fatigue performance are different for neat bitumen compared to CRMB binder. Based on the findings in this study, rubberized asphalt mixture combining with WMA additives is expected to have a promising long-term fatigue performance.

Mechanistic Assessment of Fatigue Performance and Cost Analysis of Pavement Overlays: Comparison between Conventional Hot Mixed Asphalt, Asphalt Rubber, and Polymer-Modified Mixtures

Abstract Fatigue cracking, which is commonly associated with repeated traffic loading, is considered one of the major distresses occurring in asphalt pavements because of the low tensile strength of hot mixed asphalt (HMA). Studies have shown that introducing modifiers, such as rubber and polymers, increases the tensile strength of HMA, prolonging the fatigue life of pavement. Although research in the past has studied the effect of added rubber and polymers on the long-term fatigue performance of newly constructed pavement, few studies have shown the effect of those modifiers on the fatigue life of an asphaltic overlay and their associated cost-effectiveness. In this study, the long-term fatigue performance of asphalt overlay was constructed utilizing three different mixtures, conventional HMA, asphalt rubber (AR), and polymer-modified mixtures, which were evaluated utilizing 3D Move Analysis software. In addition, cost-effectiveness analysis was performed. Eighteen 3D Move Analysis scenarios were run including two different overlay thicknesses, three different vehicle speeds, and three different overlay mixtures. The tensile strain at the bottom of the overlay was determined and the number of fatigue loading cycles to failure (Nf) was calculated based on strain-Nf relationships of the three asphalt mixtures. Based on these analyses, use of modified mixtures as an overlay resulted in a significant increase in the service life of the overlay. It was demonstrated that AR and polymer-modified mixtures had better fatigue life and were more cost-effective than the conventional HMA mixtures.

Antiageing Performance Evaluation of Recycled Engine Oil Bottom Used in Asphalt Rejuvenation

To comprehensively evaluate the antiageing performance of recycled engine oil bottom (REOB) used in asphalt rejuvenation, ageing performance studies were carried out on REOB, REOB-rejuvenated asphalt, and REOB-rejuvenated asphalt mixture. The thin film oven test (TFOT) results of REOB and a professional regenerant, RA5, were compared to verify the ageing resistance of REOB as an asphalt regenerant. The quality and viscosity of REOB-rejuvenated asphalt, RA5-rejuvenated asphalt, and base asphalt were measured after extended TFOT (ageing times for 5 h, 10 h, 15 h, 20 h, and 25 h), and the low-temperature performance of three aged asphalts was evaluated by bending beam rheological tests. The corresponding three kinds of asphalt mixtures were used to design and pave surface layers of a full-scale indoor test road. The long-term fatigue performance of indoor asphalt pavement was investigated by a self-developed rotary accelerated loading test (RALT) system. The results show that when used as an asphalt regenerant, REOB meets the antiageing requirements listed in the technical specification. The short-term (TFOT ageing time less than or equal to 10 h) ageing resistance of REOB-rejuvenated asphalt is better than that of RA5-rejuvenated asphalt but worse than that of base asphalt, whereas the long-term (TFOT ageing time greater than or equal to 15 h) ageing resistance of REOB-rejuvenated asphalt is the worst among the three tested asphalts. After long-term ageing, REOB-rejuvenated asphalt is prone to cracking at low temperatures because of its rapid increase in stiffness and sharp decrease in stress relaxation performance. Increasing temperatures increases the deflection value of asphalt pavement as the number of loading cycles increase. High-temperature ageing significantly aggravates the increase of the deflection value of REOB-rejuvenated asphalt pavement under RALT long-term loading, which makes it most prone to fatigue failure among the three pavements. Therefore, the above test results show that REOB used in asphalt pavement rejuvenation is prone to premature and excessive damage.

Experimental Investigation of the Steel-Concrete Joint in a Hybrid Tower for a Wind Turbine under Fatigue Loading

This study investigated the fatigue behaviors at the joint of a hybrid steel–concrete wind turbine tower. A fatigue design approach was proposed for the joint based on CEB-FIP model code 1990 and Eurocode 2. In addition, to estimate the long-term fatigue performance related to continuous wind changes at the joint, two types of specimens were fabricated and tested. Each specimen consisted of steel and concrete sections, which were connected with anchor bolts, and they were designed to investigate the effect of the embedded length of the anchor bolt. Two million cycles of cyclic loading were applied to the specimens, after which a monotonic static loading was applied to investigate the residual performance of each specimen. The experimental results demonstrate that the joint of a hybrid steel–concrete wind turbine tower designed using the proposed approach retained sufficient fatigue performance. Thus, this approach can be effective for fatigue design of the joint.

Application of viscoelastic continuum damage approach to predict fatigue performance of Binzhou perpetual pavements

For this study, the Binzhou perpetual pavement test sections constructed in Shandong Province, China, were simulated for long-term fatigue performance using the layered viscoelastic pavement analysis for critical distresses (LVECD) finite element software package. In this framework, asphalt concrete was treated in the context of linear viscoelastic continuum damage theory. A recently developed unified fatigue failure criterion that defined the boundaries of the applicable region of the theory was also incorporated. The mechanistic modeling of the fatigue mechanisms was able to accommodate the complex temperature variations and loading conditions of the field pavements in a rigorous manner. All of the material models were conveniently characterized by dynamic modulus tests and direct tension cyclic fatigue tests in the laboratory using cylindrical specimens. By comparing the obtained damage characteristic curves and failure criteria, it is found that mixtures with small aggregate particle sizes, a dense gradation, and modified asphalt binder tended to exhibit the best fatigue resistance at the material level. The 15-year finite element structural simulation results for all the test sections indicate that fatigue performance has a strong dependence on the thickness of the asphalt pavements. Based on the predicted location and severity of the fatigue damage, it is recommended that Sections 1 and 3 of the Binzhou test sections be employed for perpetual pavement design.

Fatigue Behavior of GFRP Reinforcing Bars in Air and in Concrete

Although the use of glass fiber-reinforced polymer (GFRP) reinforcing bars is gaining acceptance as an alternative to conventional steel reinforcement in concrete structures, little empirical data exist on the long-term fatigue performance of GFRP bars in concrete. Abrasion at the bar-concrete interface is known to have an adverse effect on bonds and on the overall member response under cyclic loading, although this effect was not adequately quantified until now. This paper presents the results of an experimental study comparing the fatigue performance of GFRP bars in air with the behavior of similar bars embedded in concrete. The experimental findings showed that the GFRP bars tested in air survived fatigue lives that were approximately a full order of magnitude longer than similar bars in concrete beams. The results were used to calibrate a statistical fatigue life model and a residual stiffness model for GFRP bars in reinforced concrete flexural members.

Computationally efficient approaches to fatigue analysis of deepwater risers

Riser long-term fatigue performance is an important design consideration. Although extensive application of irregular sea analysis in time domain with the rainflow counting technique for post-processing is regarded as the most accurate of the approaches for fatigue analysis, it does suffer from some limitations, such as the computational effort. For this reason, two computationally efficient approaches are employed to perform the fatigue analysis of a deepwater top-tensioned riser, based on the Longuet-Higgins distribution and time domain scaling respectively. With Longuet-Higgins distribution irregular wave sea states are expanded into their individual wave bins. These regular wave simulations are of short duration and consequently run quickly. Using the time domain scaling technique, the number of irregular wave runs can be performed for a comparatively small number of load cases and hence reduces the calculation time. The results showed a reasonable accuracy and significant efficiency for both approaches, compared with those from the equivalent rainflow analysis. With much less computational effort and disk storage requirement, the approaches outlined in this paper can therefore be used for the fatigue assessment of deepwater risers in industry practice.

Effect of Dental Implant Diameter on Fatigue Performance. Part II: Failure Analysis

The purpose of this study was to perform fracture mode analysis for in vitro failed implants in order to evaluate the relation between the fracture mode obtained and the implants' fatigue behavior. Eighty fractured dental implants were analyzed after being tested for fatigue performance. A macroscopic failure analysis was performed, which evaluated and located the fracture modes obtained, followed by a microscopic failure analysis comprising a detailed scanning electron microscopy (SEM) fractographic analysis. Four distinctive fracture loci were identified and macrofracture mode analysis was performed, showing that all 5-mm implants that fractured were fractured at the abutment neck and screw. In the 3.75-mm group, 44.4% were fractured at the implant neck and 55.5% at the implants second thread. Fifty-two percent of the 3.3-mm fractured implants had it at the implants second tread and 48% at the implants third thread. The implant's metallographic sections revealed that the different fracture loci were located where thin metal cross sections and sharp notches coexist. Using SEM, we were able to characterize the failure micromechanisms and fatigue characterization as transgranular fracture and arrays of secondary parallel microcracks at relatively low magnifications and classic fatigue striations at much higher magnifications. The results of this study indicate that proper implant design is crucial to ensure long-term fatigue performance for dental implants. The combination of sharp notches (thread) and narrow metal cross section is quite deleterious for fatigue resistance.

Carbon nanofibers enhance the fracture toughness and fatigue performance of a structural epoxy system

This study investigates the monotonic and dynamic fracture characteristics of a discontinuous fiber reinforced polymer matrix. Specifically, small amounts (0–1 wt.%) of a helical-ribbon carbon nanofiber (CNF) were added to an amine cured epoxy system. The resulting nanocomposites were tested to failure in two modes of testing; Mode I fracture toughness and constant amplitude of stress tension–tension fatigue. Fracture toughness testing revealed that adding 0.5 and 1.0 wt.% CNFs to the epoxy matrix enhanced the resistance to fracture by 66% and 78%, respectively. Fatigue testing at 20 MPa peak stress showed a median increase in fatigue life of 180% and 365% over the control by the addition of 0.5 and 1.0 wt.% CNF, respectively. These results clearly demonstrate the addition of small weight fractions of CNFs to significantly enhance the monotonic fracture behavior and long-term fatigue performance of this polymer. A discussion is presented linking the two behaviors indicating their interdependence and reliance upon the stress intensity factor, K.

A new masonry arch bridge assessment strategy (SMART)

About 40% of the European railway bridge stock comprises masonry arch bridges and over 60% of these are over 100 years old. All are ageing and most are carrying loads well in excess of those envisaged by their builders. The maintenance and assessment of these bridges is a constant concern for the bridge owners. Although current masonry arch bridge assessment methods are able to predict the ultimate carrying capacity of the bridge with some confidence, serious concerns have been identified with respect to predicting long-term behaviour and residual life. A new assessment procedure (sustainable masonry arch resistance technique (SMART)) is presented which differs philosophically from all the current techniques in as much as it takes a holistic approach in considering all possible modes of failure that the structure may experience under any given loading regime. Limit states are discussed and a new permissible limit state that is specific for masonry is proposed. The method advocates consideration of the permissible working loads, long-term behaviour and residual life of the bridge. This enables the assessing engineer to prioritise conflicting maintenance demands on limited budgets. The method is based upon recent research related to the long-term fatigue performance of masonry arch bridges subjected to cyclic loading.

The anti-oxidative properties of α-tocopherol in γ-irradiated UHMWPE with respect to fatigue and oxidation resistance

Although addition of an antioxidant ( α -tocopherol) is reported to prevent delamination in ultrahigh molecular weight polyethylene (UHMWPE) knee components, contribution of α -tocopherol as an antioxidant to the improvement of long-term fatigue performance of UHMWPE is an unknown mechanism. To solve this problem, bi-directional sliding fatigue tests were performed for γ -irradiated (25 kGy), γ -irradiated (25 kGy) with 0.3 wt% α -tocopherol added, and γ -irradiated (25 kGy) with 0.3 wt% tocopheryl acetate added UHMWPE specimens. Internal defect initiation was quantified with scanning acoustic tomography (SAT). Also, oxidation index and crystallinity were obtained from infrared absorption spectra measured using Fourier transform infrared (FT-IR) microscopy. Only γ -irradiated UHMWPE specimens resulted in severe fatigue fractures. α -Tocopherol-added UHMWPE specimens showed significantly lower projected area ratio of defects (1.80±0.82) than did γ -irradiated (7.0±2.29) and tocopheryl acetate-added ones (8.50±2.01). The oxidation index of γ -irradiated UHMWPE specimens (0.111±0.0052) was extremely higher compared to those of doped ones; 0.0179±0.0026 and 0.0144±0.0069 for α -tocopherol-added and tocopheryl acetate-added ones, respectively. The crystallinity of γ -irradiated UHMWPE specimens (57.5±1.16) was lower compared to those of doped ones; 60.3±0.72 and 60.4±1.38 for α -tocopherol-added and tocopheryl acetate-added ones, respectively. The incorporation of α -tocopherol significantly improves the long-term fatigue performance of γ -irradiated UHMWPE with oxidation stability. Also, the addition of α -tocopherol controls macromolecular structures resulting in the improvement of fatigue performance of UHMWPE.

Quantitative Field Evaluation and Effectiveness of Fine Mix Under Hot-Mix Asphalt Base in Flexible Pavements

Testing was conducted with the main objective of predicting the effect of incorporating a fine hot-mix asphalt (HMA) layer under an HMA base on the long-term fatigue performance of flexible pavements. Testing at the Virginia Smart Road allowed the determination of the vertical compressive stress and horizontal transverse strain induced by a steering-axle tire of 25.8 kN (5,800 lb) under the HMA layer of two pavement designs, one of which included a fine surface mix below a base mix. Stresses and strains were measured for four different speeds [8, 24, 40, and 72 km/h (5, 15, 25, and 45 mph)], for three tire inflation pressures [552, 655, and 724 kPa (80, 95, and 105 psi)], and at different temperatures. Stresses were measured with pressure cells, while strains were measured with H-type strain gauges embedded in the HMA layers during construction. As expected, temperature was found to significantly affect the vertical compressive stresses and horizontal transverse strains measured under the HMA layer. Speed, on the other hand, did not affect the magnitude of the vertical compressive stress measured in any of the layers but did affect the loading time. However, speed was found to significantly affect the horizontal transverse strain measured under the HMA layer. The compressive stress and horizontal transverse strain measured at the bottom of the HMA layer at depths greater than 150 mm (6 in.) were found to be independent of tire inflation pressure ranges from 552 to 724 kPa (80 to 105 psi). It appears that incorporation of a fine HMA at the bottom of a HMA base layer would increase the fatigue lives of flexible pavements.