Static Fatigue Research Articles

Which Functional Outcomes Can be Measured in Low Back Pain Trials and Therapies?: A Prospective 2-Year Factor-, Cluster-, and Reliability-Multicenter Analysis on 42 Variables in 1049 Individuals.

Prospective 2-year factor-, cluster-, and reliability-multicenter analysis. To provide evidence on the uniqueness and usefulness of a set of potential relevant functional outcomes. A very high number of functional outcomes that can be utilized as variables in low back pain (LBP) trials exists. Participants (n = 1049) with and without current LBP were included. At 7 visits (baseline, 4 wk, 3 mo, 6 mo, 9 mo, 1 yr, and 2 yr), 42 different functional outcomes were assessed. Two exploratory factor analyses (for baseline-values and for changes scores to 3 mo post-baseline) were calculated (maximum likelihood extraction, varimax factor rotation). The strongest factor-loading outcomes were selected for the following hierarchical cluster analyses (average linkage, Euclidean distance measure). For each cluster, time point, and outcome, reliability analyses were subsequently calculated using intraclass correlation coefficients, standard error of measurements and coefficients of variation. The factor analysis for the cross-sectional values revealed 9 factors with a cumulative variance explanation of 61.7% and 13 unique ones. The change-score factor analysis revealed nine factors with a total variance explanation of 61.8%, seven outcomes were unique. Ten outcomes were important for both cross-sectional and change-score analyses, 11 were most valuable for cross-sectional and four for the change scores. Patients with pain grades 1 to 3 show comparable patterns (cluster 2). Grade 0 (cluster 1) and grade 4 (cluster 3) are unique and cannot be cumulated with other grades. Most biomechanical outcomes were highly reliable and display low measurement errors. We found 25 potentially meaningful functional outcomes in the context of objective functional measurements (such as trunk range of motion, dynamic and static balance, strength, and muscle fatigue resistance) and body characteristics. The present framework may help to select appropriate functional outcomes and rate effects beyond the known core set of outcomes.Level of Evidence: 1.

The effect of size and stress state on the strength of architectural glass. Experiments versus theory

The multi-scale approach in the statistical evaluation of the macroscopic strength of annealed glass for architectural applications indicates a close correlation with the population of surface microcracks present in the glass sheets. The theory predicts a dependence of the strength capacity on the size of the glass element and on the state of stress acting on it. To investigate this effect, an experimental campaign has been conducted on samples of three different sizes, tested in a ring-on-ring apparatus. Data were re-normalized according to statistics of the Weibull type and re-scaled to account for the phenomenon of static fatigue. For small- and medium-size specimens, the results are in agreement with the prediction of Weibull statistical theory, according to which the larger the specimen, the greater the probability of finding cracks of critical size and, consequently, the lower the macroscopic strength on a statistical basis. On the other hand, quite surprisingly, large samples show an opposite trend. Since the state of stress is not uniform and equibiaxial in the large specimens, on the contrary to what happens in the small and medium size ones, this finding suggest a revision of classical approach based on linear elastic fracture mechanics and its correlation with the weakest-link-in-the-chain rationale in the evaluation of the mechanical properties of brittle materials such as glass.

Effect of Fillet Radius of UAV Main Landing Gear on Static Stress and Fatigue Life using Finite Element Method

The landing gear is one crucial component in the UAV aircraft structure because it serves as the main supporting component of aircraft load when landing and take-off. This study aims to determine the effect of the fillet radius on static stress and fatigue life of the main landing gear for UAV aircraft. Static stress and fatigue life analysis using the finite element method with Ansys Workbench software. The fillet radius is varied 120, 130, 140, and 150 mm. Predictions for fatigue life use the Gerber mean stress theory with a full-reserved type of loading. Landing gear material uses Aluminium alloy 6061. The static stress analysis shows that the higher the fillet radius, the higher the von Mises stress of the main landing gear frame. The fatigue life analysis shows that the higher the fillet radius, the lower the fatigue life of the main landing gear frame. The main landing gear frame achieves the highest fatigue life of up to 3.90 x 107 cycles at a fillet radius of 120 mm.

Effect of Bolt Hole Size on Static Stress and Fatigue Life of UAV Main Landing Gear Using Numerical Simulation

Currently, the use of Unmanned Aerial Vehicle (UAV) or Drone for various applications in science and engineering has increased significantly. One of the essential components of a UAV aircraft is the landing gear which plays an important role during take-off and landing. The paper research the effect of the bolt hole size on the static stress and fatigue life of main landing gear in the UAV aircraft using numerical simulation with Ansys Workbench. The bolt hole size varies 8, 9, 10, 11, and 12 mm. Gerber mean stress theory with a full-reserved type of loading is used to predict the fatigue life. The static stress simulation results show that the higher the bolt hole size, the higher the von Mises stress of the main landing gear frame. The fatigue life analysis shows that the higher the bolt hole size, the lower the fatigue life of the main landing gear frame. The main landing gear frame fails to achieve a minimum fatigue life of 1 million cycles at a 12 mm bolt hole size.

Static Fatigue of SiC/SiC Minicomposites at High Temperatures Up to 1200 °C in Air: Multiscale Approach

The present paper investigates the static fatigue behavior of Hi-Nicalon fiber-reinforced SiC–SiC minicomposites at high temperatures in the 900–1200 °C range, and under tensile stresses above the proportional limit. The stress–rupture time relation was analyzed with respect to subcritical crack growth in filaments and fiber tow fracture. Slow crack growth from flaws located at the surface of filaments is driven by the oxidation of free carbon at the grain boundaries. Lifetime of the reinforcing tows depends on the statistical distribution of filament strength and on structural factors, which are enhanced by temperature increase. The rupture time data were plotted in terms of initial stresses on reinforcing filaments. The effect of temperature and load on the stress–rupture time relation for minicomposites was investigated using results of fractography and predictions of minicomposite lifetime using a model of subcritical growth for critical filaments. The critical filament is the one whose failure by slow crack-growth triggers unstable fracture of the minicomposite. This is identified by the strength–probability relation provided by the cumulative distribution function for filament strength at room temperature. The results were compared to the fatigue behavior of dry tows. The influence of various factors related to oxidation, including multiple failures, load sharing, and variability, was analyzed.

Correlation of fatigue behavior and dynamic mechanical properties of hybrid composites of polypropylene/short glass fibers/hollow glass beads

Ternary hybrid composites of Polypropylene (PP)/Short Glass Fibers (GF)/Hollow Glass Beads (HGB) were prepared using untreated and aminosilane-treated HGB, compatibilized with maleated-PP, and with varying total and relative GF/HGB contents. Static/short-term flexural strength properties data revealed, through lower flexural strength values, that the presence of untreated HGB particles induces to fiber-polymer interfacial decoupling at much higher extent than in the presence of aminosilane-treated HGB particles. This phenomenon is also evident when evaluating the data from displacement-controlled three-point bending fatigue tests. Monitored up to 106 cycles, the analyzed hybrid composites presented distinct performance relative to their fatigue stress relaxation rate: the lower the matrix-reinforcements’ interfacial adhesion, more pronounced the stress relaxation rate as a function of the number of fatigue cycles. Dynamic Mechanical Thermal Analysis (DMTA) results could successfully reveal the hybrid composites behavior at the microstructural level when they were submitted to both static flexural test and fatigue, depending on the degree of interfacial interactions between the polymer matrix of PP and the hybrid reinforcements of GF and HGB (with and without aminosilane surface treatment).

Effects of drilling strategies for CFRP/Ti stacks on static mechanical property and fatigue behavior of open-hole CFRP laminates

Abstract Hybrid carbon fiber reinforced polymer (CFRP)/titanium alloy (Ti) stacks are the key load-bearing components in the aircraft structure. However, CFRP/Ti stack has poor machinability and defects are easily caused in the drilling process, resulting in the reduction of fatigue performance for aircraft structural parts. In this paper, the effects of drilling strategies on static mechanical property and fatigue behavior of open-hole CFRP laminates were studied by quasi-static tensile tests and fatigue tests. When drilling CFRP/Ti stacks from CFRP side, due to the hole defects of CFRP caused by Ti6Al4V chips, the ultimate tensile strength and fatigue life of open-hole CFRP laminates decrease by 12.5 % and 75.8 %, respectively. When drilling CFRP/Ti stacks from Ti6Al4V side, due to the drilling defects of CFRP caused by the high drilling temperature and delamination, the ultimate tensile strength and fatigue life of open-hole CFRP laminates decrease by 5.8 % and 26.5 %, respectively.

Structure design and reliability analysis of Al-Ti lugs

Aircraft lug joint is the key part of load transfer. In order to improve the safety of lug joint, on the premise of meeting the design requirements of static strength and fatigue, the composite connection lug structure design technology of different metal materials is proposed in this paper. Firstly, the damage safety design and life reliability analysis of the lug structure are studied theoretically. Secondly, based on the concept of damage safety design and the design principle of deformation coordination, the design method of composite connection lug with deformation coordination is proposed, and the thickness ratio of single ear is 0.8:1:0.8. Finally, the reliability of the composite lug is analyzed. The results show that the structural design scheme of aluminum-titanium composite ear piece can meet the requirements of static strength and damage tolerance, and compared with the conventional ear structure, the failure probability of structure mission life is greatly reduced when the weight of the composite connection lug is only increased by 4.9%. The proposed method can effectively guide the structural design of composite ear piece.

Investigation of the Effect of Fatigue Level on Plantar Pressure Distribution in Heavy Metalworkers

This study aims to evaluate the relationship between static plantar pressure analysis and fatigue conditions in heavy metal factory workers' routine working environments. 89 heavy metal factory workers with a mean age of 41.69 ± 9.82 were included in the study. The Fatigue level of the participants was evaluated with the “Fatigue Severity Scale. Forefoot, hindfoot and total pressure distributions of right and left feet were analyzed with the static pedobarographic devices. The relationship between the variables was evaluated by Spearman correlation analysis. No significant correlation was found between fatigue level of workers and forefoot, hindfoot and total static plantar pressure distributions of right and left foot (p>0,05). There was no significant relationship between the fatigue level of heavy metal workers and static plantar pressure distributions. In future studies, it is recommended that workers plantar pressure analyzes be evaluated dynamically during working hours.

Structural integrity assessment for ITER lower VS coil feedthrough

The ITER vertical stabilization coil system is designed to provide fast plasma stabilization in all scenarios with elongated plasma cross-section. It consists of two water-cooled coils located in upper and lower portions of the vacuum vessel (VV), with feedthroughs responsible for the transfer of electricity and cooling water across the vacuum boundary of VV. Depending on location, the feedthroughs can be divided into upper port feedthroughs (UPR feedthroughs) and lower port feedthroughs (LWR feedthroughs), each family sharing the same design. Both designs are subject to demanding operation scheme, a severe working environment and the presence of interfacing components, which impose important thermal, electromagnetic and seismic loads on the components. In particular, the LWR feedthrough, object of present paper, is more impacted by seismic loads due to the more flexible structure compared to the UPR feedthrough. During the worst seismic event, it is subjected to a vertical acceleration of 28.8 m s−2, acting on an effective mass of 249.9 kg at its first order modal mode. Furthermore, the current circulating in the conductor of the LWR feedthrough, impose significant linear forces, up to 27.7 kN m−1 during normal operation and 30.3 kN m−1 during categories I & II abnormal plasma events, respectively. Finally, the effect of differential thermal expansions of interfacing structures imposes a relative displacement between the supports up to 32.9 mm in X (radial) direction and up to 14.67 mm in Z (vertical) direction, during baking. Being part of the vacuum boundary, the feedthrough must assure confinement function under all normal and accidental loading conditions, with proper structural integrity assessment by applying analysis approach and design criteria foreseen by the applicable nuclear codes. The paper details the load types and categories, the analysis methodologies, the structural design criteria, and the assessment results in views of static stress and fatigue for the LWR feedthrough. This study could be a comprehensive reference for the structural integrity assessment of other similar components in fusion devices.

A Comparative Study of Local Heat Treatment for Enhancing Overall Mechanical Properties of Clinched Joints

Clinching technology is widely used for joining lightweight materials. It is well known that the fatigue life of clinched joints is outstanding, but its static strength is inferior to other conventional joints such as resistance spot welding joints. In this study, a post-processing method was proposed to enhance the overall mechanical performances of clinched joints in material of steel plate cold commercial steel. Based on the failure mechanism analysis, we performed quenching, a local heat treatment process, on the joining zone to improve the static strength of clinched joints. The static strength and fatigue life of clinched joints before and after quenching were compared via experimental study. The experimental results showed that the tensile–shearing strength of clinched joint increased by 60.65% and the fatigue life was extended when the joint was under high fatigue load levels after local heat treatment. Besides, metallographic test and fracture analysis were conducted to analyze the mechanism of the change of mechanical behaviors. Lath martensite was observed in the cross section of clinched joint after local heat treatment, which is the main reason for the tensile–shearing strength increase as martensite has higher strength than ferrite and pearlite. The fracture analysis showed that the fatigue fracture mode became transcrystalline rupture after local heat treatment when the clinched joint was under low fatigue load levels, which lead to the fatigue behavior of clinched joints weakened. Nonetheless, the overall mechanical properties of clinched joints were improved.

New Concept in Bioderived Composites: Biochar as Toughening Agent for Improving Performances and Durability of Agave-Based Epoxy Biocomposites.

Biocomposites are increasingly used in the industry for the replacement of synthetic materials, thanks to their good mechanical properties, being lightweight, and having low cost. Unfortunately, in several potential fields of structural application their static strength and fatigue life are not high enough. For this reason, several chemical treatments on the fibers have been proposed in literature, although still without fully satisfactory results. To overcome this drawback, in this study we present a procedure based on the addition of a carbonaceous filler to a green epoxy matrix reinforced by Agave sisalana fibers. Among all carbon-based materials, biochar was selected for its environmental friendliness, along with its ability to improve the mechanical properties of polymers. Different percentages of biochar, 1, 2, and 4 wt %, were finely dispersed into the resin using a mixer and a sonicator, then a compression molding process coupled with an optimized thermomechanical cure process was used to produce a short fiber biocomposite with Vf = 35%. Systematic experimental tests have shown that the presence of biochar, in the amount 2 wt %, has significant effects on the matrix and fiber interphase, and leads to an increase of up to three orders of magnitude in the fatigue life, together with an appreciable improvement in static tensile strength.

Static and Flexural Fatigue Behavior of GFRP Pultruded 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.

Static, fatigue and creep performance of blind-bolted connectors in shear experiments on steel-FRP joints

As traffic loads are ever increasing and bridge infrastructure is ageing, existing materials and connection methods used in renovation and new construction projects are reaching their limits. New materials, such as Fibre-Reinforced Polymer (FRP) in the form of hollow decks can be a competitive solution due to good resistance to fatigue and corrosion. By combining the stiffness provided by steel main and secondary girders with lightweight FRP decks, the properties of both materials can be efficiently utilised. However, the main restriction to the implementation of hybrid steel-FRP structures lies in a lack of knowledge regarding the level of interaction as well as efficient and durable connection solutions of FRP decks and steel girders. Adhesively bonded and grouted connections have been identified as possible connection systems, whereas limited research has been performed on bolted connections. This paper focuses on blind-bolted shear connectors. Connector performance is evaluated experimentally by means of short-term (static) experiments to determine shear resistance and long-term experiments with sustained (creep) and cyclic (fatigue) loading. A vacuum infused GFRP multi-directional laminated plate, 20 mm thick, is connected to steel plates by means of M20 blind-bolts. Static resistance, fatigue and creep behaviour of blind-bolted connectors, as a bearing type, are compared to results of a parallel experimental campaign conducted on slip-resistant injected connectors. A comparable static resistance and ductility is found. However, fatigue endurance is much lower compared to slip-resistant connectors. Therefore, due to low fatigue endurance, low initial stiffness and initial slip, the use of blind-bolted connectors is limited to applications where hybrid interaction and fatigue endurance is not required.

Experimental and theoretical assessment of the long-term strength of lightweight concrete and its components under compression and tension, taking into account the macrostructure of the material

Experimental studies of concrete static fatigue require quite laborious and time-consuming tests. Insufficient data on static fatigue for concrete and the absence of an adequate theoretical base until recently did not allow using a generalized approach to estimate static fatigue parameters for different types of concrete. The paper presents the results of extensive experimental studies on static fatigue strength under tension and compression for lightweight concrete, mortar matrix, and hardened cement paste. A theoretical equation based on the fracture mechanics approach has been proposed and discussed for approximating experimental results and predicting static fatigue strength, which can be used for normalization of this parameter. The proposed equation displays better estimates compared to this used in the energy approach and empirical formulas.

Design and fatigue analysis of an aluminium alloy aerodynamic wheel

The deployment of CAx systems has a great influence on the design of individual car components. One of the components that must meet not only aesthetic requirements but also strict safety criteria, guarantee mechanical integrity and have good aerodynamic properties, is a car wheel. Before production begins, wheels must undergo a series of numerical analyses as well as experimental tests. Based on these tests, design modifications are made so that the wheel meets the safety criteria in real operation. The aim of this paper is to present the wheel design process, including the simulation of the rotary bending test using finite elements method (FEM). The paper describes boundary conditions of the numerical model, the process of finite element mesh generation and the results of linear static analysis and fatigue analysis of an aerodynamic wheel.

Influence of Artificial Canal Lubricants on the Lifespan of One Curve File under Static and Dynamic Test Modes

Aim: This study was designed to determine the lifespan of One Curve (OC) heat-treated nickel-titanium (NiTi) rotary files operating under static and dynamic fatigue conditions using intracanal lubricants such as oil or sodium hypochlorite (NaOCl). Materials and Methods: The OC files were tested using an artificial zirconia canal. They were tested in air without any intracanal lubricant under static (Group 1) and dynamic (Group 4) modes, and after filling the canal with either oil (Group 2 and Group 5 under static and dynamic modes respectively) or 1% NaOCl (Group 3 and Group 6 under static and dynamic modes respectively). One Curve files were rotated freely in the canal at a speed of 350 rpm (continuous clockwise) under static mode until file failure occurred through fracture. In case of dynamic testing, the instruments were rotated at the same conditions in the canal, but with an additional back and forth movement until fracturing. The number of cycles to fracture (NCF) were recorded and statistically analysed using One Way ANOVA and Bonferroni tests. Results: Testing of the file in air demonstrated the lowest fatigue resistance, where the static test mode (NCF: 560 ± 8.25) was the worse than the dynamic mode (NCF: 636.81±14.49). On the other hand, the instruments tested under both static and dynamic modes in oil as an intracanal lubricant showed improved lifespans in terms of NCF (1193.89±7.96 and 1351.39 ± 7.06) compared to the same modes in NaOCl lubrication (878.89 ± 8.59 and 1093.82±39.08). Regardless of intracanal lubricant, the dynamic groups produced better results than the static ones. In terms of fractured length, significant differences were identified between the groups except between Group 2 and Group 6. Conclusions: Type of intracanal lubricant demonstrated a more influential effect on the file lifespan than the mode of cyclic fatigue (CF) test. The dynamic CF test utilising oil intracanal lubricant resulted the best improvement in the file lifespan.

Static cyclic fatigue resistance evaluation of neoniti rotary files at different insertion angles

Static cyclic fatigue resistance evaluation of neoniti rotary files at different insertion angles

FEM Analysis of the Welding Seams Geometry in Case of Fillet Welds

The role of the welding seam is to achieve the non-removable joint between two or more parts. In principle, three geometric profiles of the welding seams can be obtained: straight profile; concave profile and convex profile. In practice, this geometric shape of the weld seam profile is very important, both in terms of the resistance of the joint to static stresses and in terms of its fatigue life. There are many factors that can influence the geometric shape of the weld seam: the welding process; welding regime; the nature of the filler materials used, the rehabilitation techniques applied and others. Often, this geometric shape of the weld bead is neglected, which is particularly dangerous due to the fact that an improper geometric shape can generate low mechanical strength in static loads or poor fatigue strength in variable loads. An optimum of the geometric configuration of the welding must be found, which reconciles both situations: the mechanical resistance in case of static stresses and also the fatigue resistance in case of variable loads. In this paper, an analysis will be made with finite elements for the straight and convex profile of the welding seams in the case of fillet welds subjected to fatigue. Several elements will be considered such as: damage; total deformation; fatigue sensitivity versus loading history; equivalent von Misses stress; safety factor.

Study on equivalent static method for the analysis of fatigue behavior of reinforced concrete beam

In order to analyze the whole process of fatigue behaviours of reinforced concrete beams, an equivalent static analysis method is proposed in this paper. Firstly, the constitutive models based on the degradation of stiffness and strength and the accumulation of residual strain of concrete and reinforcement subjected to fatigue loadings are deduced and established by coupling the uniaxial constitutive model of concrete and the ideal elastic-plastic model of reinforcement under static load. Secondly, based on the similarity of concrete failure under static load and fatigue load, the equivalent relationship between fatigue and static analysis can be constructed by using the concrete residual strain as the equivalent parameter. On this basis, an equivalent static method for the analysis of fatigue behavior of reinforced concrete beam is proposed. At last, three reinforced concrete beams with rectangular section are tested, and the fatigue behaviours are analyzed by the method proposed in this paper. The numerical simulation results are compared with the field test data. The result shows that the numerical simulation results are in good agreement with the experimental results, which verifies the reliability and practicability of the method.