Real Service Conditions Research Articles

Performance and failure modes of thermal barrier coatings deposited by EB-PVD on blades under real service conditions in gas turbine

Thermal barrier coatings (TBCs) with a double columnar crystal structure of CoCrAlY/YSZ, prepared using electron beam physical vapor deposition (EB-PVD), were applied to turbine blades and tested in real gas turbine conditions. This study investigates their failure mechanisms under both actual operating conditions and simulated external loads, using three-point bending tests. The performance of full-sized, TBC-coated blades was analyzed through finite element modeling, while the thermomechanical and mechanical properties of the coatings after service were measured to support the simulation and provide insights into the failure processes. A new degradation mode, characterized by penetration cracking, was observed in the EB-PVD coatings. This behavior is linked to the columnar grain structure of YSZ and CoCrAlY, lower operational temperatures, and the reduced thickness of the YSZ layer. Surface cracks in the YSZ coating primarily occurred in regions with large curvature, where stress concentrations are higher. This study offers new insights into the failure modes of TBCs under real gas turbine operating conditions.

Defi nition of probability of refusal and average actual resource of details of cars at substandard value of an intercontrol operating time

The offered technique of definition of probability of refusal of a detail of the car and its average actual resource, allows to define values of these parameters not only at the standard intercontrol operating time established in the specifications and technical documentation, but also taking into account a casual deviation of their specification caused by real service conditions of the car.

Optimizing dispensing performance of needle-type piezoelectric jet dispensers: a novel drive waveform approach

The dispensing performance of needle-type piezoelectric jet dispenser constitutes a crucial factor that ensures the quality of additive manufacturing processes. In this paper, a novel approach is proposed to enhance the dispensing performance of needle-type piezoelectric jetting dispensers by introducing a more adaptable driving waveform based on Bézier curves. Initially, the approach considers the electromechanical coupling effect of the needle-type piezoelectric dispenser and constructs a high-precision fluid–solid coupling model of the dispensing process. Subsequently, a multi-physics field joint simulation platform combining Matlab and Fluent is established to systematically analyze control strategies in real service conditions. Next, a new driving waveform based on Bézier curves is introduced, and the control parameters are optimized using a genetic algorithm to address issues such as air bubbles in the droplets and instability of the dispensing process. The optimized waveform based on the Bézier curve reduces the volume of air suction during the dispensing process by over 20% compared to the traditional waveform and eliminates the uncontrolled vibration state of the needle in the fluid, ensuring the stability of the entire fluid refill process. Finally, the optimized control strategy is verified through experiments and compared with traditional methods. The experiment demonstrates its advantages in addressing issues with no air bubbles in the droplets and consistency of the droplets. This study provides valuable insights into optimizing the dispensing performance of needle-type piezoelectric jetting dispensers regarding control strategy.

Corrosion fatigue behaviour of Q690D high-strength steel considering the effect of coupling

During the service period of steel structures, the condition of suffering from environmental corrosions and fatigue loadings simultaneously widely exists. In this article, focusing on the corrosion fatigue behaviour of Q690D high-strength steel with consideration of the coupling effect, experimental research was conducted and the coupling effect was analysed. Corrosion fatigue coupling tests were performed with the method of electrolytic accelerated corrosion. The corrosion characteristics were studied and compared with the corrosion tests without loadings. Then, the corrosion fatigue S-N curve was established and compared with non-corroded and pre-corroded conditions. Morphology observations were carried out to further analyse the mechanisms of corrosion fatigue coupling. The results show that the fatigue resistance of Q690D high-strength steel deteriorated greatly compared with non-corroded and pre-corroded conditions, and the adverse effect of corrosion fatigue coupling on fatigue resistance cannot be neglected. The coupling effect under real engineering service conditions could be well represented with the adopted test method, taking into account the time dimension correlation between fatigue and corrosion. The established Q690D S-N curve under the corrosive environment provides important references for the residual fatigue life assessment of high-strength steel fatigue considering the effect of environmental deterioration.

Research on guided wave propagation characteristics of quartz ceramic thermal protection structure for ablation monitoring

ABSTRACT Monitoring the thermal protection structure (TPS) of hypersonic vehicles is vital for ensuring safe flight. The guided wave(GW) structure health monitoring（SHM）method is promising for TPS health monitoring due to its high sensitivity, ability to detect small damages, and wide monitoring coverage, both online and offline. However, there is currently a clear research gap in monitoring hypersonic aircraft TPS in real-service environments. This paper addresses this gap by conducting GW monitoring research on hypersonic vehicles TPS under simulated real-service conditions, involving high-temperature and high-speed airflow ablation. This study takes quartz ceramic TPS as the object, undertaking a preliminary investigation into its GW propagation characteristics. Subsequently, the TPS underwent high-temperature and high-speed oxygen-acetylene ablation at 2100°C to induce damages. GW monitoring was then conducted to capture GW signals in both undamaged and various damage scenarios. Through signal analysis, characteristic parameter extraction, and application of the damage index method, rules governing how GW signals respond to damage were established. Results indicate significant impacts on amplitude and phase of GW signals with increasing damage severity, validating the feasibility of the GW monitoring method for detecting high-temperature and high-speed airflow damage to TPS and supporting its expansion for damage monitoring.

Digital Twin for Predicting Progressive Damage in Operating Pressure Vessels

According to the definition of the French Alliance “Industry of the Future”, the digital twin is a virtual clone of a physical system or a process. It systematically implies the existence of a "digital model" coupled with the object it copies. Depending on the system concerned and the desired usage, it can be a geometric, multiphysical, functional, behavioral, and decision-making model. It must evolve over time like its real twin. It can be used to improve the control, security and optimization of production lines and factories, digital continuity at the product level, from its design to its end of life, monitoring and predictive maintenance.The digital twin appears as a reliable way to monitor operation, to evaluate the resistance and safety of pressure vessels (PVs) in real service conditions. Via the connected transducers (IoT), we can integration the life cycle information in an automatic data processing module, and finally to capitalize on all this data to optimize the design of new products.To this end, the first objective of the thesis is to contribute to the development of a methodology for real-time assessment of the integrity of pressure vessels, by implementing a predictive maintenance strategy in place of the classical and costly, preventive or curative maintenance, based on IoT and digital twin technologies. The second technological goal of the thesis is to develop methods to optimize and make reliable the design and operation of new generations of pressure structures.

Erosion behaviour of Fe-Cr-C alloys: Cast alloy versus coating

Abstract: This research focuses on the erosion wear behaviour of two Fe-Cr-C alloys with similar chemical compositions obtained using different production methods. The first alloy belongs to the high chromium cast irons (HCCI). It was made by casting, after which the samples were heat treated by annealing. The second alloy in the form of the coating was applied by the plasma transferred arc (PTA) surface welding process at the substrate material (structural carbon steel). Damage to the components of industrial plants due to erosive and/or abrasive wear is a frequent cause of failure and outages of such systems. For this reason, and to bring the experimental research closer to real service conditions, an erosion test was performed at a gas blast sand facility with a high erodent speed of 90 m/s and a higher feed rate than standard erosion testing parameters recommended in ASTM G76 standard. Microstructural characterisation of all samples was done using a scanning electron microscope (SEM). The X-ray diffraction analysis (XRD) was used to identify the phases present. Similar erosion mechanisms were observed on all tested specimens, but coated samples (PTA alloy) had a lower mass loss during the erosion test compared to cast samples (HCCI alloy), i.e. they showed better erosion resistance.

Investigation of the influence of the variable-intensity ultraviolet aging on asphalt properties

Currently, researches related to asphalt UV aging mostly based on constant-intensity UV radiation, which is not consistent with its real service condition. In this study, the variable-intensity and constant-intensity UV radiation conditions were proposed on the principle of constant total radiation. The UV-aged neat asphalt film thickness was 1 mm and 0.5 mm. The temperature sweep, frequency sweep, and multiple stress creep recovery tests were conducted to reveal the rheological properties of UV-aged neat asphalt. Moreover, the Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) tests were performed to reveal the microscopic properties of UV-aged asphalt. Regarding the constant-intensity UV-aged asphalt with 1 mm film thickness, the rutting parameter aging index (RPAI) of 9 cycles was smaller than that of RTFO-aged asphalt. The variable-intensity UV aging induced a much larger aging effect than constant-intensity UV aging for UV-aged asphalt. The ISO and ICO under variable-intensity UV aging conditions is higher than constant-intensity UV aging for the same cycles. Besides, the asphalt thickness is an essential element affecting UV aging. The aging effect increased significantly as the film thickness decreased. SEM test results have indicated that the variable-intensity UV aging caused more microscopic morphology damage to asphalt than constant-intensity UV aging. Variable-intensity UV aging test condition proposed in this study is more accurately simulate the real service conditions. It is meaningful to propose the variable-intensity UV aging process. This study provides new ideas for simulating UV aging conditions and methods in the laboratory.

Durability of CFRP strengthened RC beam after six years exposure to natural hygrothermal environment with sustained loads

Exploring the durability of Carbon Fiber Reinforced Plastic (CFRP) strengthened concrete structures is a significant focus in the field of civil engineering. The majority of the present durability studies, which investigate the combined effects of external and environmental loading on CFRP-strengthened concrete structures, are conducted in accelerated aging environments. Nevertheless, this method fails to accurately reflect the real service conditions experienced by these structures in natural hygrothermal environments. In this study, a 6-year-long natural exposure experiment is conducted on CFRP-strengthened reinforced concrete (RC) beams under sustained loads. Additionally, the static and fatigue behavior of the exposed beam is investigated through both experimental and theoretical methods. The results indicated that the ultimate load of CFRP-strengthened RC beam remained unchanged after 6 years of natural exposure, as compared to that of non-exposed beams. However, noticeable changes were observed in their fatigue performance. The fatigue life decreased by 30 %, 75 %, and 86 % at loading levels of 0.60, 0.65, and 0.72, respectively. The fatigue limit decreased by 10 % and exhibited a dense distribution of cracks. Meanwhile, a fatigue life prediction model for RC structures strengthened with CFRP after long-term exposure to natural hygrothermal environment was established. In this model, the degradation of the CFRP-concrete interface behavior was considered. Through finite element analysis, two failure modes were predicted: fracture of the main reinforcement and the CFRP-concrete interface debonding failure under fatigue load. The corresponding fatigue life times were calculated. This model agrees well with the experimental findings.

Assessment of the mechanical behavior of bonded glass-to-glass transparent epoxy adhesive joint at elevated temperatures for load-bearing elements

Glass is increasingly used as a structural material in buildings, not only for enclosing spaces but also for bearing loads. To meet architect requirements for a uniform structure without appearance disturbance, adhesively bonded joints are preferred over mechanical fasteners. However, in the construction industry, most technical guidelines cover only soft structural silicone sealants, while stiffer adhesives like epoxy resins are not considered. Alternatively, the specific transparent epoxy adhesives offer a high potential for bonded glass assemblies, enabling thinner joints and a fully transparent junction. Indeed, under real service conditions, elevated temperatures are one of the worst factors affecting the mechanical properties of structural bonded joints. Therefore, in this paper, an experimental program was conducted to evaluate the performance of transparent bonded glass joints with epoxy resin over a wide range of temperatures. Tensile and shear tests were performed on bulk-cured adhesive samples and bonded glass-to-glass block shear specimens respectively, at room temperature (RT), 40, 60, and 80 °C. The differences in surface characteristics such as roughness, wettability, and surface free energy (SFE) between both glass sides were examined. The results showed that tensile and shear strengths decreased with increasing temperatures. Furthermore, the shear strength was influenced by the surface properties of the glass sides. At all tested temperatures, the rougher bonded glass side specimens revealed higher shear strength coupled with a mixed failure while a loss of adhesion characterised the smoother glass surfaces.

Fatigue life and failure mechanism of nylon 66 cord/rubber composites under wide temperature range

This work simulates the real harsh service conditions of Fiber-reinforced polymer composites (FRPC), and the dynamic adhesion and failure mechanism of nylon 66 (PA66)-reinforced natural rubber (NR) composites under large deformation and wide temperature range are deeply studied by comprehensive analysis of the interfacial adhesion evolution, microstructure and failure damage location of the composites, interfacial heating rate, and modulus ratio of PA66/NR. The failure mechanism of PA66/NR composites is interfacial debonding at −20 °C, 25 °C and 80 °C, whereas that at 120 °C is matrix cracks. Interestingly, at −20 °C, the crack expansion at the interface is slow, and the samples show two-stage damage during fatigue, resulting in the highest fatigue life. At 80 °C, the interface heating rate and modulus ratio of the PA66/NR composites is the lowest, and thus the fatigue life is higher than that at 25 °C and 120 °C. Keywords: fiber reinforced polymer composites, fatigue life, failure mechanism.

The influence of the substrate type on the performance of an industrial cement mortar for general use

This work aims to analyze the influence of different substrates on the performance of a conventional industrial cement-based mortar. The main objective is to evaluate how different substrates influence the physical and mechanical characteristics of the applied mortar, considering that the performance of mortars is typically characterized in the laboratory without the influence of the substrate. The research methodology includes experimental data with statistical analysis (ANOVA) of the results. Several campaigns were carried out, which began with the detailed characterization of the industrial cement mortar under study and various substrates. At the same time, the mortar was applied to the substrates and, after hardening, was detached and characterized through the same tests. These tests were based on the standards, with the necessary adaptations due to the different mortar dimensions after detachment. As a result, it was possible to conclude that the substrates where a mortar is applied must be considered a variable in its composition, considering that they influence the final behavior of the applied mortar. After application to the substrates, the mortar's performance differs from that of standardized laboratory samples. It was also concluded that ceramic, concrete and lightweight aggregate substrates influence the mortar's characteristics differently, especially the open porosity and the average pore diameter. For ceramic substrates, the characteristic that seems to influence the behavior of the mortar is capillary water absorption; for concrete substrates, it appears to be open porosity. The possibility of a transfer of water between mortar and substrate generates local changes in the water content, affecting the binder concentration and the compactness of the mortar especially noted at the interface region. The study can contribute to selecting more compatible mortars and improving the performance of the applied mortars in real service conditions.

Waveform impact on thermo-mechanical fatigue crack growth of a non-crystallizing rubber: Experimental observation and numerical simulation

Compared with the sine waveform, the pulse waveform load is more in line with the real service condition of tire. It was investigated the effect of two pulse waveform loads on the thermo-mechanical fatigue crack growth rate (FCGR) of filled styrene-butadiene rubber and explained the underlying mechanism. The fatigue test and infrared thermal imaging test revealed that the shorter the pulse excitation time, the higher the heat build-up and the faster the FCGR. The underlying mechanism was explained by an established thermo-mechanical coupling method, and it was pointed out that the faster FCGR under high-frequency loading condition resulted from higher hysteresis energy rather than higher strain energy. The Parallel Rheological Framework model could not explain this phenomenon well.

Ageing tests closer to real service conditions using hyper-sensitive microcalorimetry, a case study on EPDM rubber

Accelerated thermal ageing (ATA) coupled to mechanical testing is widely used to predict the lifetime of polymeric products. ATA implies that the mechanisms of ageing are the same at accelerated and service conditions, which may often not be the case. Hence, ageing closer to service conditions is of high importance, but require very sensitive tools. Therefore, a high sensitivity microcalorimetry (MC) method was applied here to assess if it can be a possible tool for lifetime/ageing prediction closer to service conditions. We chose to focus on a complex, yet commonly used, ethylene-propylene-diene terpolymer (EPDM) rubber. Arrhenius extrapolation of the heat flow data indicated two regimes at low and high temperature, with the former having the lower activation energy. The heat flow values measured by the MC revealed contributions from processes such as the melting of the antioxidant, its consumption at low temperature and the breakdown of residual peroxide. MC tests on the EPDM indicated a very low degree of oxidation appearing above 100 °C, too low to be observed with infra-red spectroscopy (FTIR), but noticeable with MC. The high sensitivity of the MC techniques enabled detection of early signs of polymer degradation/ageing and other thermally activated processes that take place at or close to service temperatures (such as those in nuclear power plants). The MC tests were combined with other techniques, such as scanning electron microscopy/energy dispersive X-ray spectroscopy, gas chromatography techniques, differential scanning calorimetry and FTIR to further understand the degradation mechanisms.

Durability of BFRP bars embedded in seawater sea sand coral aggregate concrete in simulated seawater environment: Effects of coral coarse aggregate and cement contents

This study evaluates the influences of coral coarse aggregate (CCA) and cement contents on the durability performance of basalt fiber-reinforced polymer (BFRP) bars embedded in seawater sea sand coral aggregate concrete (SSCC). The evaluation is conducted by characterizing the changes in interlaminar shear strength after accelerated exposure in a simulated seawater environment. Accelerated aging tests were conducted under varying exposure durations (60, 120, and 180 days) and temperatures (25, 40, and 55 °C). The 1H low-field nuclear magnetic resonance, Fourier transform infrared spectroscopy, and scanning electron microscopy analyses were conducted to investigate the deterioration mechanisms of embedded BFRP bars. It was found that SSCC-embedded BFRP bars typically have a lower interlaminar shear strength than that of seawater sea sand concrete (SSC)-embedded BFRP bars subjected to the same immersion conditions. This is mainly attributed to the high porosity of CCA, resulting in higher permeability of SSCC than that of SSC. In addition, increasing cement content enhances the initial amount of OH– in SSCC, expands the pitting area of BFRP bars, and maintains OH– concentration better in the exposure tests, accelerating the interlaminar shear strength deterioration of BFRP bars. Microstructure analysis clearly reveals that the deterioration of embedded BFRP bars is mainly caused by resin hydrolysis, fiber-resin interface debonding, and fiber damage after corrosion. Based on the Arrhenius relationship, accelerated aging test results were utilized to predict the service life of SSCC-embedded BFRP bars under the real service condition. The findings of this study are valuable for the application of BFRP bars reinforced SSCC structures under marine environments and provide some insights into improving the long-term performance of SSCC-embedded BFRP bars, i.e., modifying the CCA to minimize the permeability of SSCC and producing low-alkalinity SSCC.

Ageing of Crumb Rubber Modified Bituminous Binders under Real Service Conditions

Due to their environmental advantages, crumb rubber modified asphalt binders constitute an interesting alternative to conventional binders for road surfaces of a more durable and sustainable nature. However, in practice, they remain less commonly used than conventional polymer modified binders. This research aims to study the real ageing of crumb rubber modified asphalt binders during their service lives when exposed to various factors, including temperature gradients, the presence of water and oxidation. To this end, research was conducted on a selection of highways built with these binders and located in regions with severe climatic and traffic conditions. The binders from cores of highway surface layers were recovered and tested using the DSR (Dynamic Shear Rheometer) to determine the evolution of the rheological parameters. Crumb rubber modified asphalt binders were studied in comparison with traditional polymer modified bitumen. The analysis of the complex modulus and phase angle was conducted based on frequency and temperature sweep tests, while the evolution of the elastic recovery, Jnr, L-Index and T-Index were assessed from the multiple stress creep and recovery test. The results obtained indicate that crumb rubber modified binders show similar ageing and rheological parameters to those of conventional polymer modified bitumen, even under severe traffic and climate conditions. Furthermore, it was observed that, at high temperatures, the effect caused by real service life ageing was different to that obtained in the laboratory through the RTFO and PAV tests.

Damage Analysis of Hybrid Composites Under Multi-Impact Loads: An Experimental and Numerical Study

Laminated composite structures are subjected to impact damage during maintenance and manufacturing operations and their life service. Driven by the necessity to value damage tolerance and durability of composite materials, an analysis of multi-hit impact is conducted to reproduce the real service conditions. Despite many studies in the literature investigated the properties of composites at low impact velocity, in contrast the behavior of the hybrid configuration, especially at repeated impacts, result still little known. This work presents an experimental and numerical study of the dynamic behavior at the repeated low-velocity impact of a carbon and glass fibers hybrid composite laminate.

Structural validation of geothermal water basins constructed with durability enhanced ultra high performance fiber reinforced concrete (Ultra High Durability Concrete)

Ultra-High Performance Concrete (UHPC) proved to be very durable in harsh environments, primarily because of the extremely low porosity of the matrix (uncracked). However, the limited availability of design standards is still a barrier to widespread applications of UHPC, together with still limited knowledge of its durability in the real (cracked) service conditions. In this paper, the use of tailored UHPC is introduced, whose composition has been specifically designed to achieve enhanced durability in the cracked state combined with extremely aggressive environments. Validation of the material and structural design concept on a full scale structure is presented, with reference to a tank intended to contain geothermal water from the cooling tower at a geothermal power plant. This pilot structure was designed and constructed using both ordinary reinforced concrete and durability enhanced UHPC, which is called hereafter Ultra High Durability Concrete (UHDC), for comparative assessment purposes. Upon the completion of the pilot construction and entering its service life, periodic assessment and validation tests have been carried out to validate the structural design assumptions and to check the serviceability requirements. Results of these tests, performed over the span of two years are reported in detail in this paper to validate the material and structural concepts. The study highlights the most important parameters that could affect the performance of UHPC structures during casting and service life. The overall project framework presented in this paper has to be intended as a pioneer study in moving towards a performance based durability-design approach for UHPC structures.

Dry in-pile fracture test (DRIFT) for separate-effects validation of ceramic fuel fracture models

Fracture is an important component of nuclear fuel behavior, and significant efforts have been invested into developing fuel performance models that are capable of accurately representing fracture. Usable data on the process of fracture propagation in nuclear fuel under realistic service conditions are very limited. To address this need, a series of separate-effects experiments were developed and performed at Idaho National Laboratory's Transient Reactor Test (TREAT) facility. These experiments employ a heat sink to radially remove heat from the fuel in a manner that approximates the effect of coolant in an operating light-water reactor (LWR). The test holder for these experiments is known as the Dry In-pile Fracture Test (DRIFT). A series of experiments employing DRIFT and TREAT were performed to provide data on the extent and nature of fracture in fresh fuel at various points during a ramp to full power. Novel aspects of these experiments include the way they employ a heat sink to replicate steady-state LWR conditions, as well as the use of fiber optic sensors for in-reactor thermal instrumentation. Details on the development of this experiment, experimental conditions, and resulting data (including in situ thermal measurements and post-irradiation imaging of fracture) are provided in this paper. LWR-equivalent powers ranging from 10 to 25 kW/m were tested using this apparatus. Cracking was visible at all power levels, with increasing cracking extent as the power level increased, although there was little difference in the cracking between the two highest-power tests, which had LWR-equivalent powers of 20 and 25 kW/m.

Development of an Independent Front Suspension for Truck Tractors

Design and experimental validation stages of an independent front suspension (IFS) that is designed for truck tractors of articulated commercial vehicles are summarised. Firstly, the suspension geometry, which satisfies the required conditions of minimum deviation of camber angle and track width during wheel travel, is obtained within the given design volume by using Multibody Systems (MBS) and Design of Experiments (DOE) approaches. Subsequently, the kinetic analysis is carried out for the suspension system and the critical design loads that may act on the structural elements are determined. Taking these loads into account, the mechanical design of the suspension system elements is performed. The Finite Element Analysis (FEA) is applied to the complete suspension system for the chosen critical load conditions. Stress concentrated regions on the crucial system elements are determined and improvements are indicated, which result in the reduction of stress concentrations. In the last part of the study, prototyping and fatigue tests are carried out. Throughout bench tests, in which real service conditions are simulated, no failure of any sort is encountered. The final suspension system (pair) is 31% lighter than an equivalent rigid front axle in terms of load capacity.