Fast Fatigue Research Articles

Fast fatigue characterization by infrared thermography for additive manufacturing

High cooling rates and strong temperature gradients occurring during additive manufacturing (AM) by laser beam melting (LBM) are known to affect mechanical performances of the produced parts, and particularly fatigue properties. Mechanical properties strongly depend on the process parameters such as laser power, scan speed and laser spot size. A fatigue analysis was performed in this study by using infrared thermography to assess heat sources associated with fatigue damage. In particular, mechanical dissipation was identified thanks to suitable acquisition parameters. A model for the relationship between mechanical dissipation and mechanical solicitation was proposed and applied to two promising steels in LBM AM field, namely maraging 18Ni300 and L40 tool steel.

Корекція негативної поведінки у дітей старшого дошкільного та молодшого шкільного віку засобами соціально­педагогічних і реабілітаційних ігор

The article provides with the analysis of psychological and pedagogical literature on correctional opportunities of rehabilitation and social pedagogical games in preventing negative behavior of preschoolers and primary school children. The concepts "game" and "game activity" are characterized; the priority of games incorrecting children's physical development, health and behavior is defined. The author analyzes the existing classifications of games and proves the efficiency of application of two major games categories, i.e. rehabilitation and social pedagogical ones, according to the main directions of correctional activity, namely health-improving and social and educational. The paper explicates the expediency of rehabilitation games usage to correct physical health, speech development disorders, psychophysiological processes of memory, attention, imagination, thinking, prevention of fast fatigue and reduced working capacity, as well as attests the capacity of social and pedagogical games in correction of children's aggression, impulsiveness, uneasiness, dishonesty, indifference, inclination to negative habits; education of diligence, diligence, politeness, responsiveness, truthfulness, goodwill, and humanity.

Al-Si piston alloy behavior under combined mechanical and thermal cyclic loading with superimposed high-frequency thermal cycling

Abstract On pistons for diesel direct injection engines, the thermally high loaded bowl rim is exposed to high-cycle mechanical and high-cycle thermal loading during each combustion event in addition to the thermal cycling induced by variable engine loading, e. g. between idle and full load. This combined loading at various overall temperatures during engine operation contributes to material damage and finally to a limited service life. In the past, the high-cycle thermal loading has neither been experimentally investigated nor incorporated into a numerical model for lifetime estimation. The work described in this paper deals with the setup of an experimental test procedure on samples taken from components for which the effects of slow temperature cycling, fast temperature cycling and mechanical cyclic fatigue loading can be combined in different ratios. The aim of the investigation is to characterize the sample lifetime with respect to varied test conditions in order to differentiate alloy- or process-related material variations in support of process and material development.

Adaptation of motor unit contractile properties in rat medial gastrocnemius to treadmill endurance training: Relationship to muscle mitochondrial biogenesis.

This study aimed at investigating the effects of 2, 4 and 8 weeks of endurance training on the contractile properties of slow (S), fast fatigue resistant (FR) and fast fatigable (FF) motor units (MUs) in rat medial gastrocnemius (MG) in relation to the changes in muscle mitochondrial biogenesis. The properties of functionally isolated MUs were examined in vivo. Mitochondrial biogenesis was judged based on the changes in mitochondrial DNA copy number (mtDNA), the content of the electron transport chain (ETC) proteins and PGC-1α in the MG. Moreover, the markers of mitochondria remodeling mitofusins (Mfn1, Mfn2) and dynamin-like protein (Opa1) were studied using qPCR. A proportion of FR MUs increased from 37.9% to 50.8% and a proportion of FF units decreased from 44.7% to 26.6% after 8 weeks of training. The increased fatigue resistance, shortened twitch duration, and increased ability to potentiate force were found as early as after 2 weeks of endurance training, predominantly in FR MUs. Moreover, just after 2 weeks of the training an enhancement of the mitochondrial network remodeling was present as judged by an increase in expression of Mfn1, Opa1 and an increase in PGC-1α in the slow part of MG. Interestingly, no signs of intensification of mitochondrial biogenesis assessed by ETC proteins content and mtDNA in slow and fast parts of gastrocnemius were found at this stage of the training. Nevertheless, after 8 weeks of training an increase in the ETC protein content was observed, but mainly in the slow part of gastrocnemius. Concluding, the functional changes in MUs’ contractile properties leading to the enhancement of muscle performance accompanied by an activation of signalling that controls the muscle mitochondrial network reorganisation and mitochondrial biogenesis belong to an early muscle adaptive responses that precede an increase in mitochondrial ETC protein content.

Rapid Determination of the Fatigue Limit by the Simulation of Self-Heating Test by the Collaborative Model Based On the Fractional Derivative Approach

This paper proposes a method for on the fast fatigue limit estimation for composite materials using a simulation of a self-heating test. The experimental method based on the material self-heating was successfully applied for composite materials and allows to determine a material’s endurance limit in a few hours. In order to increase the potential of this experience, the thermomechanical modelling is proposed with the precise description of the intrinsic energy dissipation. The rise of material’s temperature is linked with development of plastic strains, material damage, viscoelastic proprieties of polymer matrix and intro-crack friction. Therefore, the collaborative behaviour model including the hysteresis loops is used to represent the visco-elastoplastic damage composite behaviour. The collaborative model consists of two sub-models. The first one describes an envelope of the loading curves and insures the computation of elastic and the in-elastic strains as well as the in-ply damage. The second part deals with modelling of hysteresis loops during unloading path using a fractional derivative approach. Just a few parameters are required to represent the hysteresis loops. Using a proposed modelling, the dissipation due to the in-ply damage propagation, the material hardening and the viscoelastic effects can be precisely calculated. The fatigue limit is determined by using thermodynamic simulation the quasi-static cyclic test with the dissipation measurements as an equivalent to self-heating test. The method is validated for composite materials with thermosetting and thermoplastic matrixes.

Fast fatigue life prediction of short fiber reinforced composites using a new hybrid damage approach: Application to SMC

Abstract Industrial design of Short Fiber Reinforced Composites (SFRC) structures is subject to several compounding and processing steps of optimization. Moreover, these structures are often submitted to fatigue loading. Therefore, SN curves have to be established for each new composite formulation and for several type of microstructure involved in the real component due to processing. While these preliminary characterizations are time and money consuming, this paper propose a new hybrid methodology for fast fatigue life prediction. Moreover, both monotonic and fatigue behavior of SMC composites is essentially determined by local damage propagation. Therefore, the key idea of the proposed approach is to use a Mori and Tanaka based micromechanical model in order to establish an equation of state relating local damage rate to macroscopic residual stiffness rate. The generalization of this relation to fatigue damage multi-scale description leads to the SN curve fast determination of each considered microstructure. Very limited experimental characterization is required in such a way that SN curve could be established in just one day. Comparison between experimental and simulated Wholer curves highlights a very good agreement for several microstructure configurations in the case of a SMC composite material.

Mixed-mode I/II delamination fatigue strengthening of polymer composites using z-pins

An experimental investigation is presented into the improvement to the delamination fatigue resistant properties of z-pinned carbon fibre–epoxy composite under mixed-mode I/II cyclic interlaminar loading. Delamination fatigue tests are performed on unpinned and z-pinned composites under different mixed-mode ratios spanning mode I to mode II interlaminar cyclic conditions. The fatigue resistance and fatigue strengthening mechanisms induced by the z-pins is dependent on the cyclic mixed-mode ratio. The threshold critical strain energy release rate needed to initiate delamination growth in the z-pinned composite increases with the GI-to-GII ratio. The fatigue crack growth rate slows considerably and the critical strain energy release rate for fast fatigue fracture increases with the GI-to-GII ratio. The delamination fatigue strengthening induced by the z-pins increases with the GI-to-GII ratio due to a transition in the crack bridging toughening process from pin pull-out under mode I dominated loads to combined tensile and shear fracture under mixed-mode loads to pin shear rupture under mode II dominated loads. It is also found that the effect of the GI-to-GII ratio on the fatigue properties is greater for the z-pinned composite compared to the unpinned laminate due to the high fatigue sensitivity of z-pins to the mixed-mode ratio.

Особенности адаптационных ресурсов мирных жителей, проживающих в зоне вооруженного конфликта, в контексте изучения трансформаций личности

The article presents the data of an empirical study of the features of the adaptation resources of the population living under the conditions of the armed conflict. The study involved 723 people of both genders living in the immediate area of the armed conflict, their age ranging from 17 to 75 years old. It is empirically shown that the respondents of the first group (areas of low-intensity shelling) are generally characterized by high activity, cheerfulness, calmness, healthy optimism, they are active and satisfied with life; these indicators are more pronounced in women aged 19-35 years. It is established that in the first group almost half of the respondents show a high level of neuropsychic resistance; a higher level of it being observed in men. It has been determined that the respondents of the second group (areas of intensive shelling) are characterized by displays of irritability, anxiety, and also depression, despair. They are characterized by fast fatigue, low working capacity, lethargy, reduced energy potential and emotional stability, moral normalization. This group of people shows an average neuropsychic resistance, there are signs of stress and mental disadaptation (mainly in women aged 35-60 and older), they are less satisfied with life on the whole than the respondents of the first group, and they also give a lower estimate of their personal success. Most pronounced these indicators were in women 19-35 years old and in men 35-60 years old. It is also established that the subjects of both groups reveal a high level of personal adaptation potential, as evidenced by their rapid adaptation to the new reality conditions. The most adaptive in the first and second groups are young people aged 17-19, and also women aged 19-35. The main conclusions of this study are as follows: long-term residence in the area of the armed conflict, especially in the areas of intense shelling, significantly affects the adaptation capacity of a person, activates his life resources, on the one hand, and, on the other hand, it may have negative consequences for the mental health and lead to disadaptation, and a decrease in the adaptation potential.

Symptomatic isolated thoracic splenosis 11 years after abdominal trauma: Case report

Thoracic splenosis is defined as the autotransplantation of splenic tissue into thorax. It occurs due to splenic rupture in association with a diaphragmatic tear on the left side after a traumatic event. It is a rare disease that most commonly remains undiscovered as it is usually asymptomatic. We present a symptomatic case of thoracic splenosis in a 53-year-old smoker male patient with a medical history of abdominal surgery and splenectomy for a thoracoabdominal gunshot. Three years before the medical examination he was suffering from dyspnea, frequent coughing, left pleuritic chest pain and complained about faster fatigue. A chest radiograph obtained during a medical checkup showed a multinodular left pleura-based mass in the upper lobe. Established histopathological diagnosis after surgical removal of the nodule was splenosis. No evidence of malignancy was observed. Splenosis should be considered as a differential diagnosis by the undertaken workup of left pulmonary nodules or masses in patients with a history of trauma.

Effect of interaction of embedded crack and free surface on remaining fatigue life

Embedded crack located near free surface of a component interacts with the free surface. When the distance between the free surface and the embedded crack is short, stress at the crack tip ligament is higher than that at the other area of the cracked section. It can be easily expected that fatigue crack growth is fast, when the embedded crack locates near the free surface. To avoid catastrophic failures caused by fast fatigue crack growth at the crack tip ligament, fitness-for-service (FFS) codes provide crack-to-surface proximity rules. The proximity rules are used to determine whether the cracks should be treated as embedded cracks as-is, or transformed to surface cracks. Although the concepts of the proximity rules are the same, the specific criteria and the rules to transform embedded cracks into surface cracks differ amongst FFS codes. This paper focuses on the interaction between an embedded crack and a free surface of a component as well as on its effects on the remaining fatigue lives of embedded cracks using the proximity rules provided by the FFS codes. It is shown that the remaining fatigue lives for the embedded cracks strongly depend on the crack aspect ratio and location from the component free surface. In addition, it can be said that the proximity criteria defined by the API and RSE-M codes give overly conservative remaining lives. On the contrary, the WES and AME codes always give long remaining lives and non-conservative estimations. When the crack aspect ratio is small, ASME code gives non-conservative estimation.

Early dysregulation of trigeminal motor pool excitability in a mouse model for neurodegenerative motoneuron disease

Amyotrophic Lateral Sclerosis (ALS) is a progressive neurodegenerative motoneuron (MN) where in fast fatigable motor units (MUs) of vulnerable motor pools preferentially degenerate followed by fast fatigue resistant and slow MUs . Excitability is a key endogenous mechanism of MN neuroprotection [1] and therefore we hypothesize that pre-symptomatic excitability indicates impending disease development. Using a transgenic mouse model for ALS, we performed in vitro patchclamp electrophysiology in ALS-vulnerable trigeminal motoneurons (TMNs) retrogradely labeled from jaw closer muscles at P8-12. We proposed a novel k-means clustering approach to classify TMNs into putative fast fatigable (PFF), fast fatigue resistant (PFR) and slow (PS) MUs based on rheobase and input resistance. Interestingly, hyper-excitability was noted in PFF and PFR

Reconsideration of the fatigue tests for asphalt mixtures and binders containing high percentage RAP

When applying reclaimed asphalt technology in a flexible pavement project, most performance concerns are related to low temperature and fatigue cracking since the stiffness of the HMA mixture could dramatically increase through adding a high percentage of reclaimed asphalt pavement (RAP) material. The purpose of this study is to evaluate asphalt mixtures with high RAP contents, prepared using two RAP addition methods, for their performance based on fatigue-cracking resistance rather than relying on volumetric properties. Asphalt mixture samples were prepared with three RAP binder content replacement percentages (30, 40 and 50%) using two preparation methods: the as-is RAP gradation (traditional method) and the splitting of the RAP gradation into coarse and fine fractions (fractionated method). Asphalt mixture beam fatigue and binder fatigue time-sweep tests were performed. Beam fatigue samples also underwent freeze–thaw cycling for freeze–thaw damage evaluation. Rather than basing the performance based solely on S–Nf curves to illustrate the fatigue performance, the beam fatigue test data was analysed through a dissipated energy approach. Faster fatigue degradation was observed for the 40% RAP binder and beam mixture when subjected to repeated loading. From a morphology aspect, this can be explained by the binder’s phase separation and physical hardening effects.

Aerodynamic Interference Effect of Huge Wind Turbine Blades With Periodic Surge Motions Using Overset Grid-Based Computational Fluid Dynamics Approach

The accurate prediction of unsteady aerodynamic performance and loads, for floating offshore wind turbines (FOWTs), is still questionable because several conventional methods widely used for this purpose are applied in ways that violate the theoretical assumptions of their original formulation. The major objective of the present study is to investigate the unsteady aerodynamic effects for the rotating blade due to the periodic surge motions of an FOWT. This work was conducted using several numerical approaches, particularly unsteady computational fluid dynamics (CFD) with an overset grid-based approach. The unsteady aerodynamic effects that occur when an FOWT is subjected to the surge motion of its floating support platform is assumed as a sinusoidal function. The present CFD simulation based on an overset grid approach provides a sophisticated numerical model on complex flows around the rotating blades simultaneously having the platform surge motion. In addition, an in-house unsteady blade element momentum (UBEM) and the fast (fatigue, aerodynamic, structure, and turbulence) codes are also applied as conventional approaches. The unsteady aerodynamic performances and loads of the rotating blade are shown to be changed considerably depending on the amplitude and frequency of the platform surge motion. The results for the flow interaction phenomena between the oscillating motions of the rotating wind turbine blades and the generated blade-tip vortices are presented and investigated in detail.

Development of subliminal persuasion system to improve the upper limb posture in laparoscopic training: a preliminary study.

Current training for laparoscopy focuses only on the enhancement of manual skill and does not give advice on improving trainees' posture. However, a poor posture can result in increased static muscle loading, faster fatigue, and impaired psychomotor task performance. In this paper, the authors propose a method, named subliminal persuasion, which gives the trainee real-time advice for correcting the upper limb posture during laparoscopic training like the expert but leads to a lower increment in the workload. A 9-axis inertial measurement unit was used to compute the upper limb posture, and a Detection Reaction Time device was developed and used to measure the workload. A monitor displayed not only images from laparoscope, but also a visual stimulus, a transparent red cross superimposed to the laparoscopic images, when the trainee had incorrect upper limb posture. One group was exposed, when their posture was not correct during training, to a short (about 33 ms) subliminal visual stimulus. The control group instead was exposed to longer (about 660 ms) supraliminal visual stimuli. We found that subliminal visual stimulation is a valid method to improve trainees' upper limb posture during laparoscopic training. Moreover, the additional workload required for subconscious processing of subliminal visual stimuli is less than the one required for supraliminal visual stimuli, which is processed instead at the conscious level. We propose subliminal persuasion as a method to give subconscious real-time stimuli to improve upper limb posture during laparoscopic training. Its effectiveness and efficiency were confirmed against supraliminal stimuli transmitted at the conscious level: Subliminal persuasion improved upper limb posture of trainees, with a smaller increase on the overall workload.

Experimental, theoretical and numerical fatigue damage estimation using a temperature modified Dirlik method

This article describes experimental, theoretical and numerical fatigue damage estimation using a temperature modified Dirlik method. The method enables an estimation of high cycle fatigue damage for uniaxial loadings caused by random vibrations directly from power spectral analyses with the temperature effect. Preliminary investigations of high cycle fatigue properties of high pressure die-cast aluminium alloy AlSi9Cu3 have been carried out at elevated temperatures. Standard and non-standard fatigue tests have been performed to determine the temperature dependent S–N curves. Simultaneously, fatigue damage estimation was carried out numerically with commercial programmes Ansys Workbench and LMS Virtual.Lab using finite element methods. Finally, the numerical simulation results are compared with both experimental and theoretical results. The temperature modified Dirlik method enables a computationally fast fatigue damage estimation of random stress loadings and temperature histories.

Numerical analyses of bending fatigue of four-step three-dimensional rectangular-braided composite materials from unit cell approach

This paper reports the numerical analyses of three-point bending fatigue behavior of four-step three-dimensional braided composite with three types of representative unit cell (RUC) model. The three types of unit cell models are the unit cell model for the interior, surface, and corner regions of the three-dimensional braided composite. A user-defined material subroutine was developed to characterize the stiffness matrix and fatigue damage evolution of the unit cells and furthermore the braided composite. The fatigue bending behaviors were calculated from the unit cell model with finite element method. It is found that the stress concentration and large deflection located at the middle of the braided composite specimen and both the ends of the bottom areas. As the increase of the stress level, the braided composite is subjected to larger deformation and faster damage accumulation, resulting in a fast fatigue failure. The RUC model could be extended to predict and design the bending fatigue performance of other three-dimensional braided composite structures.

Carbonic Anhydrase III Contributes to Fatigue Tolerance and Recovery of Skeletal Muscle

Carbonic anhydrase III (CA3) is a metabolic enzyme with a potential role in regulating intracellular pH. CA3 is highly expressed in slow twitch skeletal muscles. Here we demonstrated that mouse tibialis anterior (TA), a fast twitch muscle, also expresses a high level of CA3 while its myofilament protein contents were similar to that of CA3-negative extensor digitorum longus (EDL) muscle. To investigate the function of CA3 in muscle contractility and tolerance to fatigue, we studied skeletal muscles of CA3 knockout (Car3-/-) mice. Sciatic nerve stimulation-generated in situ contractility of EDL and TA muscles were examined in comparison with wild type controls. The results of isometric twitch and tetanic contractions showed no significant difference between TA and EDL muscle of wild type mice or between Car3-/- and wild type TA muscles. Nonetheless, intermittent fatigue treatment revealed faster fatigue and slower recovery of wild type TA muscle than that of wild type EDL muscle. Car3-/- TA muscle exhibited slower and less fatigue but also slower recovery than that of wild type TA muscle, whereas the ultimate level of force recovery was unchanged. It is suggested that CA3 increases the sensitivity of muscle to fatigue, which might serve as an acute physiological protection. In the meantime, Western-blot detected a low molecular weight fast troponin T (TnT) variant specifically in TA muscle of adult Car3-/- mice, suggesting a chronically adaptive response through alternative RNA splicing. The role of CA3 in fatigue tolerance and recovery of skeletal muscle suggests a molecular therapeutic target for functional enhancement.

Excitation BolsTORs Motor Neurons in ALS Mice

It is unclear why motor neurons selectively degenerate in amyotrophic lateral sclerosis (ALS). Saxena etal. (2013) demonstrate that excitation of motor neurons can prevent their demise in a mouse model of inherited ALS by a mechanism involving the mTOR pathway.

Accelerated lifetime estimation of thermosonic Cu ball bonds on Al metallization

In this study a fast mechanical shear fatigue test technique for the quality assessment of thermosonic ball bonded interconnects was developed to estimate their lifetime behavior. The micro-interconnects were subjected to cyclic shear stress using a special specimen set-up in combination with an ultrasonic resonance fatigue system at a frequency of 20kHz and a laser Doppler vibrometer for velocity measurements. Two different types of power semiconductor devices comprising single and multiple Cu ball bonds on Al pads of the same dimension and bonding quality were tested to validate the proposed testing technique. Due to the dimensional restrictions of both specimen types, suitable sample preparation techniques were designed to induce cyclic shear stresses in the interface of the ball bonded interconnects. The obtained high cycle fatigue life curves could be related to the specimen design and the resulting loading modes. Using FEM simulations the loading modes and fatigue response of both set-ups were analyzed. Life-time prediction curves based on a Basquin type relationship (von Mises stress - loading cycles) were obtained in which dissimilar geometries and loading modes could be equated. Additional SEM investigations of the fractured areas were compared and discussed to understand the microstructural failure mechanisms occurring during fatigue loading. It can be concluded that this new fatigue testing technique accompanied by FEM simulations and subsequent inspection of the fractured area is a suitable time saving and economic testing method for the assessment of the reliability and fatigue life response of small micro-interconnects.

Validation of temperature modified Dirlik method

The paper presents the validation of a temperature modified Dirlik method. This method enables an estimation of high cycle fatigue damage for uniaxial loadings caused by random vibrations directly from a known power spectral analysis with the temperature effect. High cycle fatigue properties of high pressure die-cast aluminium alloy AlSi9Cu3 are investigated at elevated temperatures. Standard fatigue tests are performed to determine the temperature dependent S–N curves. In the next step special fatigue tests are developed and performed to validate the temperature modified Dirlik method. Finally, the numerical simulation results are compared with the experimental results. The temperature modified Dirlik method is tested successfully. Besides, it enables a computationally fast fatigue damage estimation of random stress loadings and temperature histories.