Overload Research Articles

Morning versus Nocturnal Heart Rate and Heart Rate Variability Responses to Intensified Training in Recreational Runners

BackgroundResting heart rate (HR) and HR variability (HRV) are widely used parameters to assess cardiac autonomic nervous system function noninvasively. While resting assessments can be performed during sleep or after awakening, it would be relevant to know how interchangeable the results of these measurements are. This study aimed at examining the alignment between nocturnal and morning assessments during regular endurance training and in response to intensive training. A total of 24 recreational runners performed a 3-week baseline period (BL) and a 2-week overload (OL) period (Lucia’s training impulse + 80%). Their running performance was assessed with a 3000-m running test after the BL and OL. The participants recorded daily their nocturnal HR and HRV (the natural logarithm of the root mean square of successive differences; LnRMSSD) with a photoplethysmography-based wrist device and performed an orthostatic test (2-min supine, 2-min standing) every morning with a chest-strap HR sensor. The HR and LnRMSSD segments that were analyzed from the nocturnal recordings included start value (SleepStart), end value (SleepEnd), first 4-h segment 30 min after detected sleep onset (Sleep4h), and full sleep time (SleepFull). The morning segments consisted of the last-minute average in both body positions. All segments were compared at BL and in response to the 3000-m test and OL.ResultsAll nocturnal HR and LnRMSSD segments correlated with supine and standing segments at BL (r = 0.42 to 0.91, p < 0.05). After the 3000-m test, the HR increased and LnRMSSD decreased only in the SleepStart, Sleep4h, and SleepFull segments (p < 0.05). In response to the OL, the standing HR decreased (p < 0.01), while the LnRMSSD increased (p < 0.05) in all segments except for SleepStart. The Pearson correlations between relative changes in nocturnal and morning segments were − 0.11 to 0.72 (3000-m) and − 0.25 to 0.79 (OL). The OL response in Sleep4h HR and LnRMSSD correlated with the relative change in 3000-m time (r = 0.63, p = 0.001 and r=-0.50, p = 0.013, respectively).ConclusionsNocturnal and morning HR and LnRMSSD correlated moderately or highly in the majority of cases during the BL, but their responses to intensive training were not similarly aligned, especially in LnRMSSD. The nocturnal segments seemed to be sensitive to physical loading, and their responses were associated with the performance-related training responses.

Different outcomes of endurance and resistance exercise in skeletal muscles of Oculopharyngeal muscular dystrophy.

Exercise is widely considered to have beneficial impact on skeletal muscle aging. In addition, there are also several studies demonstrating a positive effect of exercise on muscular dystrophies. Oculopharyngeal muscular dystrophy (OPMD) is a late-onset autosomal dominant inherited neuromuscular disorder caused by mutations in the PAPBN1 gene. These mutations consist in short (1-8) and meiotically stable GCN trinucleotide repeat expansions in its coding region responsible for the formation of PAPBN1 intranuclear aggregates. This study aims to characterize the effects of two types of chronic exercise, resistance and endurance, on the OPMD skeletal muscle phenotype using a relevant murine model of OPMD. In this study, we tested two protocols of exercise. In the first, based on endurance exercise, FvB (wild-type) and A17 (OPMD) mice underwent a 6-week-long motorized treadmill protocol consisting in three sessions per week of running 20cm/s for 20min. In the second protocol, based on resistance exercise generated by chronic mechanical overload (OVL), surgical removal of gastrocnemius and soleus muscles was performed, inducing hypertrophy of the plantaris muscle. In both types of exercise, muscles of A17 and FvB mice were compared with those of respective sedentary mice. For all the groups, force measurement, muscle histology, and molecular analyses were conducted. Following the endurance exercise protocol, we did not observe any major changes in the muscle physiological parameters, but an increase in the number of PABPN1 intranuclear aggregates in both tibialis anterior (+24%, **P=0.0026) and gastrocnemius (+18%, ****P<0.0001) as well as enhanced collagen deposition (+20%, **P=0.0064 in the tibialis anterior; +35%, **P=0.0042 in the gastrocnemius) in the exercised A17 OPMD mice. In the supraphysiological resistance overload protocol, we also observed an increased collagen deposition (×2, ****P<0.0001) in the plantaris muscle of A17 OPMD mice which was associated with larger muscle mass (×2, ****P<0.0001) and fibre cross sectional area (×2, ***P=0.0007) and increased absolute maximal force (×2, ****P<0.0001) as well as a reduction in PABPN1 aggregate number (-16%, ****P<0.0001). Running exercise and mechanical overload led to very different outcome in skeletal muscles of A17 mice. Both types of exercise enhanced collagen deposition but while the running protocol increased aggregates, the OVL reduced them. More importantly OVL reversed muscle atrophy and maximal force in the A17 mice. Our study performed in a relevant model gives an indication of the effect of different types of exercise on OPMD muscle which should be further evaluated in humans for future recommendations as a part of the lifestyle of individuals with OPMD.

Effects of single overloads on fatigue crack propagation behaviour of AZ31B magnesium alloy under different temperatures

An experimental study examined the influence of single overload ratio (OLR) on fatigue crack growth (FCG) behaviour in AZ31B magnesium alloy at different temperatures (300 K, 373 K, and 473 K). The results showed that FCG rates and stress intensity factor ranges (ΔK) vary with temperature and overload ratios. After applying a single overload (OL), the FCG rate initially decreased, then increased rapidly, and stabilized at a value consistent with constant amplitude loading (CAL). The fatigue life increased by 86 % to 143 % at 300 K, 75 % to 132 % at 373 K, and 75 % to 134 % at 473 K for OLRs ranging from 1.75 to 2.25 when compared to the fatigue life at CAL. A single overload accumulates energy at the crack tip, forming an overload region with tearing ridges, secondary cracks, dimples, and fatigue striations under varying temperatures.

Overload-induced anisotropy of fatigue crack growth in laser deposited Ti–6Al–4V alloy

Considering the anisotropy of microstructure of additive manufactured metal materials, quantitative assessment of the anisotropy of fatigue crack growth (FCG) behavior is necessary for structural damage tolerance design and evaluation. This study conducted an experimental and mechanistic investigation of the FCG behavior of the laser metal deposited (LMD) Ti–6Al–4V alloy, focusing on the anisotropy of FCG and the effect of overload on FCG. Both the FCG experiments with constant amplitude loading (CAL) and with a single overload (OL) were performed in different directions. Under CAL, the FCG rate exhibits a bilinear correlation with the stress intensity factor. Before the transition point (ΔKT = 16.9 MPa√m), since the grain boundaries are sparser along the columnar crystal growth direction, the FCG rate in the XY specimen is higher than that in the other directions. When the FCG rate further increases, the hindrance effect of grain boundaries on FCG weakens, and the anisotropy of FCG rates disappears. An interesting new finding is that when an overload is applied after ΔKT, the FCG rates in the XZ and ZX directions become different, and the overload-induced anisotropy increases with the overload ratio (OLR). The difference in FCG rates between the two directions exceeds 23.2% when OLR is 2.5. Based on microscopic and theoretical analysis, it was demonstrated that the overload induces residual strain in front of the crack-tip and enhances FCG resistance. The FCG resistance is positively related to the size of the plastic zone and negatively related to the yield strength in the loading direction.

An investigation into the influence of variable amplitude creep-fatigue loading on plasticity-induced crack closure

Finite element simulations of fatigue crack growth (FCG) and creep-fatigue crack growth (CFCG) under constant amplitude (CA) and variable amplitude (VA) loading waveforms are performed to investigate the mechanics of crack opening and closing, which has implications on crack growth rate. The material of study is the ferritic-martensitic steel 9Cr-1Mo (modified 9Cr-1Mo) at 625 °C. Two-dimensional finite element analyses of compact tension (CT) specimens are performed to simulate crack growth under several VA loading scenarios, considering elastic–plastic and creep deformations of the material at the crack tip. In this study, the relevant variable influencing crack growth rate is the crack opening load, caused by the phenomenon of plasticity-induced crack closure. A series of loading conditions were simulated using the finite element method, i.e., fatigue overload (OL) in either CA FCG or CFCG waveforms, creep-fatigue OL in CFCG waveforms, and underload (UL) in CFCG waveforms. The crack opening loads obtained from this study for CA loading in both FCG and CFCG, agree with data from published studies. This study also found that a significant reduction in crack opening loads is experienced by the growing crack when an OL or UL cycle was introduced. Immediately after the OL or UL cycle is applied, the crack opening load increases during both fatigue OL and creep-fatigue OL to values larger than those recorded during CA FCG and CFCG loading, whereas UL waveforms result in consistently lower crack opening loads. The increase in crack opening loads is proportional to both the extent of OL and the duration of hold time in the OL cycle. However, following the application of a UL, the crack opening loads in the subsequent cycles were not influenced by the magnitude of the UL or the duration of hold time in the UL cycle.

Thickness and weld orientation effects on fatigue crack growth after a single tensile overload

Numerical calculations were performed to investigate the effects of thickness and weld orientation on welding residual stress (WRS) and fatigue life after a single tensile overload (OL) using a centrally-cracked steel specimen. First, welding simulations were carried out to predict WRS due to the change in thickness and weld orientation. The WRS was then considered in elastic-plastic crack growth calculations in addition to the single tensile OL. A rigorous discussion was conducted to explain the effects of thickness and weld orientation on the state of the local stress ahead of the crack tip, crack driving force, and fatigue life.

Contribution of overload-induced residual stress to fatigue retardation pertinent to notch geometry

Incorporating tensile overload (OL) or notch to a fatigue-cracked specimen could prolong fatigue life, but the combined effect of both is unclear up to now. To clarify combined effect of OL-induced residual stress (RS) and notch geometry on subsequent fatigue crack growth (FCG), fatigue tests are carried out by a combination of OL conditions, notch geometries and stress-intensity values. After incorporating notch into a post-OL specimen, the results show that fatigue retardation only results from notch effect at early fatigue phase and then from OL-induced RS later. Additionally, the magnitude of FCG-rate changing and crack-propagation length influenced by notch are related to notch geometry and applied stress ratio, respectively.

Fatigue short crack growth: Overload-induced acceleration/retardation behavior

In-situ test was conducted to investigate the effect of overload (OL) on fatigue short crack growth rate (FSCGR). Mechanisms of dual crack growth competitions and overload-induced acceleration/retardation were revealed using digital image correlation (DIC) technology. Eventually, the plastic zone sizes obtained by DIC and Irwin model were compared to propose an OL-induced model to describe FSCGR.

Fault classification of three phase induction motors using Bi-LSTM networks

The induction motors are back bone of the modern industry and play very important role in manufacturing and transportation sectors. The induction motor faults are mainly classified into internal faults such as inter turn short circuits , broken rotors and external faults such as over load, over voltage faults and asymmetry in supply voltage. The identification of type of fault is very important for safe operation and for preventing risk of machine failures. In this work, a Bidirectional Long Short Term memory networks (Bi-LSTM)-based machine learning methodology is proposed for classification of external faults of Induction Motors. The line voltages of the three phases and the three line currents are considered as the inputs to the Bi-LSTM network for identifying types of fault. Line voltage and line current data sets are considered for six different types of fault conditions. The six different conditions of the three phase induction motor are normal output (NO), overload (OL), over voltage (OV), under voltage (UV), Voltage unbalance (VUB) and single phasing (SP). The BI-LSTM network is trained using Adam optimization algorithm. The classification results are obtained with Bi-LSTM network are compared with LSTM networks to show the advantage of the proposed approach.

Effect of post-weld heat treatment on mechanical properties and fatigue crack growth behaviour of friction stir welded 7075-T651 Al alloy

The effect of post weld heat-treatments (PWHT) on the mechanical and fatigue crack growth of friction stir welded 7075-T651 aluminum alloy was investigated. The PWHT of natural aging (NA), artificial aging at 190 °C for 24 h (HT1), and 423 °C for 12 h (HT2) resulted in significant improvement in the mechanical properties of the welded joint as compared to the base metal. The highest improvement in mechanical strength is seen in HT1 post heat treatment followed by NA and HT2 post heat treatments. The ductility of welded joint for PWHT at 190 °C with a soaking period of 24 h is about 70 % of the base metal. Crack growth tests at constant amplitude loading (CAL) and single tensile overload (OL) with an overload ratio of 1.8 were conducted at a stress ratio of 0.1. A difference in the crack growth rates after application of overload is seen in all PWHT conditions. Different heat treatments did not change the growth behaviour in base metal in both the loading cases. However, a slight difference in crack growth rates is observed due to the application of overload. The crack growth acceleration followed by delayed retardation is observed due to the application of overload. The post weld heat treatment enhances the retardation effect due to tensile overload and the degree of enhancement depends on the PWHT.

Stress intensity-dependent relation between overload plastic zone and fatigue retardation in Al-alloy

Unveiling tensile overload (OL) influence during constant amplitude fatigue is fundamental to life prediction of random fatigue load. Although the same OL results in the same plastic-zone size for a material, subsequent fatigue retardation strongly depends on applied stress intensity, e.g. stress ratio R. This study attempts to separate the contributions of OL-induced residual stress (RS) related to crack closure and applied stress, crack-tip damage zone (DZ), and R-ratio depended crack deflection. To this end, fatigue tests are comparatively analyzed based on combination of different R ratios, the same OL condition, and removing DZ and crack-tip plastic zone. The results show that the fatigue retardation induced by the same OL decreases with increasing R, and the delay retardation disappears after removing DZ at R = 0.7 case. In addition, the OL-induced crack deflection is more obvious at low R = 0.1–0.4 cases than that at R = 0.7 case.

The study on the overloading effect on fatigue crack growth considering residual stress relaxation in Al 5456-H38

A numerical and experimental study was conducted on fatigue crack growth (FCG) of metallic components to investigate the effect of redistribution of mechanical residual stresses induced by overloading in notched specimens. The compact tension (CT) specimens of an aluminum alloy were used, and mechanical residual stresses were introduced in them by applying tensile overload (OL). Then, the specimens were subjected to fatigue loading. In the calculations of finite element method (FEM), the modified cyclic J-integral was used as the crack growth parameter. Good agreement was observed between the numerical and experimental results. The FEM results demonstrated a clear redistribution of residual stresses during FCG process. It was observed that after a few cycles, the residual stress field reached a lower magnitude value confining in a small zone around the around the crack tip. Furthermore, the effects of stress ratio, load amplitude, and OL ratio (OLR) on the redistribution of residual stresses are studied in this research. It was observed that the residual stresses are considerably released during the initial cycles of fatigue loading.

Fatigue crack growth under overload/underload in different strength structural steels

Aiming at the different strength-level structural steels, fatigue crack growth rate (FCGR) tests were conducted under a series of loading conditions, i.e., constant amplitude load (CAL), single overload (OL), single underload (UL), or periodic underloads (PULs). Meanwhile, the effects of various baseline loading stress ratios on the FCGR were considered. To analyze the effects of crack-tip behavior on the crack propagation following an OL/UL, the crack-tip strain fields and crack opening displacement were obtained by digital image correlation (DIC). It was found that when the OL/UL-amplitude was constant, the fatigue crack propagations under the OL/UL were affected by both steel strengths and baseline loading stress ratios. In general, an increase in the steel strength grade indicated a lower crack retardation/acceleration during the OL/UL process, which was more evident under the lower baseline stress-ratio condition. The higher the strength, the lower the crack-opening stress level, the smaller the plastic zone size, and the higher the crack-tip residual strain. Correspondingly, there were different variations in the instantaneous FCGR and OL/UL-affected cycles. When the OL/ULs are considered in the design stage, our work can guide the steel strength grade selection and provide a better understanding of the crack growth retardation/ acceleration mechanisms.

Investigation of the Flow Field and the Pressure Recovery in a Gas Turbine Exhaust Diffuser at Design, Part-Load, and Over-Load Conditions

Abstract The performance of axial diffusers installed downstream of heavy duty gas turbines is mainly affected by the turbine load. Thereby the outflow varies in Mach number, total pressure distribution, swirl and its tip leakage flow in particular. To investigate the performance of a diffuser at different load conditions, a generic diffuser geometry has been designed at ITSM which is representative for current heavy duty gas turbine diffusers. Results are presented for three different operating conditions, each with and without tip flow, respectively. Part-load (PL), design-load (DL) and over-load (OL) operating conditions are defined and varied at the diffuser inlet in terms of Mach number, total pressure distribution, and swirl. Each operating point is investigated experimentally and numerically and assessed based on its flow field as well as the pressure recovery. The diffuser performance shows a strong dependency on the inlet swirl and total pressure profile. A superimposed tip flow only influences the flow field significantly when the casing flow is weakened due to casing separation. In those cases, pressure recovery increases with additional tip flow. There is a reliable prediction of the computational fluid dynamics (CFD) simulations at design-load. At part-load, CFD overpredicts the strut separation, resulting in an underpredicted overall pressure recovery. At over-load, CFD underpredicts the separation extension in the annular diffuser but overpredicts the hub wake. This leads to a better flow control in CFD with the result of an overpredicted overall pressure recovery.

Effect of crack-tip deformation on fatigue crack growth: A comparative study under overload/underload conditions

With the aim to provide the structural design stage with data on the crack retardation/acceleration effects caused by overload/underload and to explore the corresponding mechanisms, we conducted a series of comparative fatigue crack growth rate (FCGR) tests on S355J2W+N steel. The various amplitudes of overload/underload were investigated comprehensively under different stress-ratio baseline loads for single and periodic overloading/underloading processes. Moreover, the crack-tip deformation behaviors (i.e., the strain/stress fields and crack closure responses following the overload/underload) were observed using a digital image correlation (DIC) technique and calculated through the finite element analysis. The relevant fracture morphologies and crack-tip dislocation structures were characterized and analyzed. The results showed that the crack propagation cycles could be influenced to different degrees by a single overload (OL), a single underload (UL), and periodic underloads (PULs). Compared with the transient crack acceleration induced by a UL, a lasting crack growth retardation occurred following an OL. The OL&UL sequences had various effects on the changes in FCGR. Furthermore, a higher stress-ratio baseline loading and larger-amplitude OL increased the retardation effect; a lower stress-ratio baseline loading and larger-amplitude UL enhanced the acceleration effect. The degrees of crack retardation or acceleration following the OL/UL were determined by the changes in the crack closure and residual stress state near crack tip, which were closely related to the baseline loading stress ratio and local residual strain characteristics. Correspondingly, the OL and PULs also changed the dislocation density and structures in the microscopic view.

Characterization of discontinuous crack closure behavior after the application of a single overload cycle

This paper aims to analyze the discontinuous crack closure behavior observed after a single tensile overload (OL) under otherwise constant ΔK loading. The investigation was performed on a disk-shaped compact tension DC(T) specimen made of Al6351-T6 with thickness of 2 mm, in order to simulate the case of a crack propagating under plane stress conditions. The Digital Image Correlation (DIC) technique was used in situ to obtain the full-field displacement and strain solution around the crack surfaces during the fatigue crack propagation. The experimental data obtained from DIC analysis revels that the residual hump of stretched material left in the wake of the propagating crack by the overload acts like a compliant spring, leading to a discontinuous crack closure mechanism. Moreover, this residual hump has a significant effect on the post-overload transient crack growth, even at distances much larger than the plastically deformed area created by the overload in front of the crack tip.

OC/OL Protection of Droop-Controlled and Directly Voltage-Controlled Microgrids Using TMF/ANN-Based Fault Detection and Discrimination

In this article, we propose a generalized overcurrent (OC) and overload (OL) protection scheme for the droop-controlled and directly voltage-controlled (DVC) inverter-interfaced distributed energy resources (IIDERs) to be used for the protection studies of the alternating-current (ac)-islanded (autonomous) microgrids, and provide a management strategy during and after short circuit (SC) and consequent OLs. The fault is detected, and its type is discriminated by a new method that takes the advantages of both artificial neural networks (ANNs) and transient monitoring function (TMF). By using the proposed strategy, the output current magnitudes of the distributed energy resource (DER) units are limited, and after fault clearance, the microgrid is restored to its normal operating conditions. The proposed OC/OL protection scheme limits the output power of the DERs. In this regard, a generalized fault model is presented, which considers the effect of the control system of the IIDERs. This model exploits a current-limiting strategy (CLS) that can be implemented in different reference frames to enhance the microgrid fault ride-through (FRT) capability. Finally, to demonstrate effectiveness, accuracy, authenticity, and feasibility of the proposed OC/OL protection scheme along with the TMF/ANN-based fault detection method and their desirable performance, offline digital time-domain simulations are done in MATLAB/Simulink environment, and the results are experimentally verified by using the OPAL-RT real-time digital simulator (RTDS).

A comprehensive coordinated frequency control scheme for double- fed induction generator wind turbine, battery, and diesel generators in islanded microgrids

ABSTRACT This paper proposes a comprehensive strategy for the coordinated frequency control of a low-inertia islanded microgrid (MG). The main components of the MG include a double-fed induction generator (DFIG)-based wind turbine, a battery energy storage system (BESS), and diesel synchronous generators (DGs). In the proposed control framework, effective but simple coordination between the DFIG and the BESS is developed to handle the responsibility of fast-primary frequency support (PFS) and compensate for the deficiencies of DGs in providing the fast frequency response during sudden load disturbances. To minimize the consumption of BESS energy, the proposed coordinated control utilizes the maximum support capacity of the DFIG bound by the over-deceleration (OD) and overload (OL) constraints. The coordinated BESS prevents the OD and OL issues of DFIG during the support period, and compensates the shortages of the DFIG wind system for the certain frequency support under any wind condition. It also prevents the secondary frequency drop issue during the DFIG rotor speed recovery. To return to the normal condition after fulfilling the PFS functions, the DFIG and BESS support powers are brought back to zero via a secondary frequency control (SFC) applied in the DGs. In normal conditions, to optimally manage the MG energy efficiency, the BESS exchanged power is set to zero, and the DFIG is controlled in the maximum power point tracking (MPPT) operation through an efficient algorithm. A test system with a 33% load disturbance is modeled in a detailed time-domain simulation environment to evaluate and verify the effectiveness of the proposed design methodology. The simulation results show the superiority of the proposed coordinated control strategy compared with only DFIG or only BESS control under various wind conditions.

Effect of endurance exercise duration on muscle hypertrophy induced by functional overload.

For many ball games, both resistance and endurance training are necessary to improve muscle strength and endurance capacity. Endurance training has been reported to inhibit muscle strength and hypertrophy, but some studies have reported that endurance exercise (EE) does not inhibit the effects of resistance exercise. Here, we examined the effect of short- or long-duration EE on mouse skeletal muscle hypertrophy induced by functional overload (OL) at the molecular level. Plantaris muscle hypertrophy was induced by OL with synergist ablation in mice. Body mass was reduced with endurance training, but EE duration (30 or 90min) had no effect. The ratio of plantaris muscle weight to body weight was higher in the OL and EE for 30 min (OL+EE30) and OL and EE for 90 min (OL+EE90) groups compared with the OL group. Expression of mechanistic target of rapamycin signaling proteins, which is related to protein synthesis and hypertrophy, was increased in the OL+EE30 group. Expression of Forkhead box-containing protein O1, which is related to protein breakdown and atrophy, remained unchanged. However, microtubule-associated protein 1 light chain 3, a known marker of autophagy, and MAFbx, which is related to protein breakdown, were significantly increased in the OL+EE90 group. Furthermore, markers of oxidative stress, ubiquitin and 4-hydroxynonenal were also significantly increased in the OL+EE90 group compared with other groups. In conclusion, EE duration did not affect body mass and plantaris mass and did not interfere with mechanistic target of rapamycin signaling, but it did increase ubiquitinated proteins and oxidative stress. It is therefore necessary to consider training durations for EE when combining endurance and resistance training.

Critical investigation on the effect of steel strength on fatigue crack growth retardation including a single tensile overload

The effect of steel strength on fatigue crack growth (FCG) retardation was investigated considering the influence of a single tensile overload (OL) by means of FEM. A technique that combines a fracture mechanics approach and an elasto-plastic material model available in WARP3D, an open source code, was applied. The interaction integral method provided by WARP3D was used to calculate stress intensity factor solutions based on the local stress fields obtained by elasto-plastic analyses. Crack growth calculations were then performed using ΔK obtained by the numerical analyses. FCG material properties were proposed for the employed steels based on elasto-plastic analyses where the residual stress fields induced by local plasticity ahead of the crack tip was considered. Calculated fatigue lives under two different loading patterns were verified with experiments. The results revealed that steel strength has a significant influence on the size of the induced plastic zone, crack geometry and the behavior of ΔK in particular after the OL. In addition, it is found that steel strength has a pronounced effect on the induced local stress field ahead of the crack tip as well as it exhibits a considerable influence on FCG retardation due to the OL. It is also noticed that, after the OL, the higher the steel strength the smaller the size of the induced plastic zone ahead of the crack tip as well as the higher the produced ΔK. This leads to accelerate FCG rate and shorten the resulting FCG retardation in which it influences the component service life.