Experimental Test Campaign Research Articles

Influence of in-plane transverse compression on the behaviour of the face plate component in weak axis and tubular steel joints

The behaviour of the face-plate component under out-of-plane loading has been previously studied, and analytical formulations characterizing the initial stiffness have been proposed. However, research investigating the response of this component under simultaneous transverse loading is limited. This study examines the influence of in-plane transverse compression on the out-of-plane behaviour of the face-plate component in weak axis and tubular beam-to-column steel joints. An experimental test campaign was conducted, covering five representative joint configurations for connections to both I-section and tubular columns. Finite element models of the tested specimen were generated and validated based on the test results. Subsequently, these results were supplemented by two sets of numerical parametric studies, encompassing a total of 329 connections under different levels of transverse loads. The results indicate the detrimental effect of transverse compression on the stiffness and resistance of the face-plate component. Analytical expressions for the reduction of initial stiffness under compressive in-plane transverse loads were proposed and validated, facilitating easy incorporation into design standards.

EXPERIMENTAL STUDY OF THE INFLUENCE OF INCIDENTAL OVERLOADS ON THE FATIGUE BEHAVIOR OF SHEETS ASSEMBLED BY SPOT WELDS

The assembly of steel sheets using the spot-welding process is commonly used in the automotive industry - notably at Renault - for the production of the chassis. The stresses encountered in service due to rough roads or driving conditions are transmitted between assembled components via the welded points. Understanding their fatigue behavior under incidental overloads is therefore essential for ensuring their service life and permanently dimensioning the structure. In the present study, an experimental test campaign was conducted to analyze the fatigue failure modes of two identical steel plates joined by welded points and loaded in tension-shear. Two high-strength steel grades (HE360D and XE360D) and one mild steel grade for deep drawing (XES) were tested either at constant amplitude, or with incidental stresses occurring at a rate of one overload cycle for every 100 cycles applied. All cycles had a load ratio of 0.1 (undulating tension). The assembly of steel sheets using the spot-welding process is commonly used in the automotive industry - notably at Renault - for the production of the chassis. The stresses encountered in service due to rough roads or driving conditions are transmitted between assembled components via the welded points. Understanding their fatigue behavior under incidental overloads is therefore essential for ensuring their service life and permanently dimensioning the structure. In the present study, an experimental test campaign was conducted to analyze the fatigue failure modes of two identical steel plates joined by welded points and loaded in tension-shear. Two high-strength steel grades (HE360D and XE360D) and one mild steel grade for deep drawing (XES) were tested either at constant amplitude, or with incidental stresses occurring at a rate of one overload cycle for every 100 cycles applied. All cycles had a load ratio of 0,1 (undulating tension). The experimental results show that periodic overloading is beneficial to fatigue life in the case of high-strength steels, whereas the effect recorded is, on the contrary, a very marked collapse in fatigue properties in the case of mild steels.

Fatigue Behaviour of High-Performance Green Epoxy Biocomposite Laminates Reinforced by Optimized Long Sisal Fibers.

In recent decades, in order to replace traditional synthetic polymer composites, engineering research has focused on the development of new alternatives such as green biocomposites constituted by an eco-sustainable matrix reinforced by natural fibers. Such innovative biocomposites are divided into two different typologies: random short fiber biocomposites characterized by low mechanical strength, used for non-structural applications such as covering panels, etc., and high-performance biocomposites reinforced by long fibers that can be used for semi-structural and structural applications by replacing traditional materials such as metal (carbon steel and aluminum) or synthetic composites such as fiberglass. The present research work focuses on the high-performance biocomposites reinforced by optimized sisal fibers. In detail, in order to contribute to the extension of their application under fatigue loading, a systematic experimental fatigue test campaign has been accomplished by considering four different lay-up configurations (unidirectional, cross-ply, angle-ply and quasi-isotropic) with volume fraction Vf = 70%. The results analysis found that such laminates exhibit good fatigue performance, with fatigue ratios close to 0.5 for unidirectional and angle-ply (±7.5°) laminates. However, by passing from isotropic to unidirectional lay-up, the fatigue strength increases significantly by about four times; higher increases are revealed in terms of fatigue life. In terms of damage, it has been observed that, thanks to the high quality of the proposed laminates, in any case, the fatigue failure involves the fiber failure, although secondary debonding and delamination can occur, especially in orthotropic and cross-ply lay-up. The comparison with classical synthetic composites and other similar biocomposite has shown that in terms of fatigue ratio, the examined biocomposites exhibit performance comparable with the biocomposites reinforced by the more expensive flax and with common fiberglass. Finally, appropriate models, that can be advantageously used at the design stage, have also been proposed to predict the fatigue behavior of the laminates analyzed.

Development and Testing of a Helicon Plasma Thruster Based on a Magnetically Enhanced Inductively Coupled Plasma Reactor Operating in a Multi-Mode Regime

A disruptive Electric Propulsion system is proposed for next-generation Low-Earth-Orbit (LEO) small satellite constellations, utilizing an RF-powered Helicon Plasma Thruster (HPT). This system is built around a Magnetically Enhanced Inductively Coupled Plasma (MEICP) reactor, which enables acceleration of quasi-neutral plasma through a magnetic nozzle. The MEICP reactor features an innovative design with a multi-dipole magnetic confinement system, generated by neodymium iron boron (NdFeB) permanent magnets, combined with an azimuthally asymmetric half-wavelength right (HWRH) antenna and a variable-section ionization chamber. The plasma reactor is followed by a solenoid-free magnetic nozzle (MN), which facilitates the formation of an ambipolar potential drop, enabling the conversion of electron thermal energy into ion beam energy. This study explores the impact of an inhomogeneous magnetic field on the heating mechanism of the HPT and highlights its multi-mode operation within a pulsed power range of 200 to 500 W of RF. The discharge state, characterized by high-energy electron-excited ions and low-energy excited neutral particles in the plasma plume, was analyzed using optical emission spectroscopy (OES). The experimental testing campaign, conducted under pulsed power excitation, reveals that, as RF input power increases, the MEICP reactor transitions from inductive (H-mode) to wave coupling (W-mode) discharge modes. Spectrograms, electron temperature, and plasma density measurements were obtained for the Helicon Plasma Thruster within its operational envelope. Based on OES data, the ideal specific impulse was estimated to exceed 1000 s, highlighting the significant potential of this technology for future LEO/VLEO space missions.

Experimental investigation of a small-scale reversible high-temperature heat pump − organic Rankine cycle system for industrial waste heat recovery

Innovative technologies are required to mitigate the challenges of climate change. A reversible high-temperature heat pump (HTHP) − organic Rankine cycle (ORC) system can be used for effective utilisation of industrial waste heat in the lower temperature band <100 °C. The system can provide useful process heat for industrial processes by operating in HTHP mode or generating power in ORC mode. This paper presents the experimental investigation of the reversible system in both HTHP and ORC modes. A single scroll unit was selected for the compressor (HTHP) and expander (ORC) roles, keeping the system compact. A HCFO refrigerant, R1233zd(E), with a low GWP value, was chosen as the working fluid for both operating modes. When operated in HTHP mode, a maximum compressor overall isentropic efficiency of 73.4 % and a COPmech of 4.8 (ΔTlift,rside = 41 K, Tsf,ev,in = 60 °C) was obtained. In ORC mode, the maximum net power output was 512.4 W (Tsf,ev,in = 90 °C, rp = 2.3), overall cycle efficiency was 3.01 %, and overall isentropic efficiency of the expander was 54.6 %. The technical limitations encountered, and solutions put in place during the experimental testing campaign are discussed in detail.

Kinetic Model Implementation of Fluidized Bed Devolatilization

Computational modeling is a powerful tool for studying and investigating the behavior of fluidized bed gasifiers and the modeling of the initial devolatilization step is necessary to provide a reliable description of the whole process involving the feedstock decomposition and the subsequent gasification reaction. In this work, a bench-scale fluidized bed reactor was used to examine the devolatilization of different carbonaceous materials within the temperature range from 650 to 850 °C. The experimental test campaign was used to derive the linear correlation factor to describe the devolatilization in terms of product distribution as a function of temperature and highlight the different behavior between lignocellulosic and plastic feedstocks. Furthermore, the experimental data were used to develop concise kinetic expressions able to fit the experimental devolatilization times ranging from 75 in the case of poplar at a lower temperature and 22 s for the Organic Fraction of Municipal Solid Waste (OFMSW) at a higher temperature. The obtained model produces a simple kinetic expression where the size of the particle is enclosed in the kinetic parameters. The kinetic model sided by the application of linear correlations describes the overall thermal decomposition in a fluidized bed, simplifying its modeling in commercial simulation software, even when particles are considered as point-like bodies.

Wave Loads On Hydraulic Structures

Hydraulic structures are essential for flood protection, water management and navigation in coastal, delta and lake regions. Their importance will continue to grow in the coming years and decades, because of two main factors. Firstly, because of the consequences of climate change and sea level rise. Secondly, because of the continuous development and urbanization of coastal, delta and lake regions, with an increase in the value of the assets and activities in those locations combined with more strict safety requirements. Those factors will lead to the construction of a series of new hydraulic structures and the renovation of several existing structures around the world. Wave loads acting on such hydraulic structures are crucial for their design and safety assessment. This study addresses two different types of wave loads acting on hydraulic structures: confined wave impact loads and bimodal wave loads. To this end, a series of laboratory experimental test campaigns were carried out in a wave flume.

Calibrating the Livengood–Wu integral knock model for differently sized methanol engines

Experimental test campaigns have begun to demonstrate the potential of methanol as an alternative fuel for heavy-duty spark-ignited engines. However, there is no consensus yet on the scope of this solution in terms of maximum power and engine size. A zero-dimensional combustion model is therefore being developed outside the scope of this work. Its main objective will be to predict key performance parameters such as power and efficiency as function of engine size. Due to the high loads typically encountered in heavy-duty engines, knock will be the main constraint to maximize the engine's potential. This work therefore aims to find an accurate knock model that can be implemented in the modelling framework. The Livengood–Wu knock integral model is being considered as a good candidate, as it is computationally inexpensive and thus allows for a large number of engine configurations to be modelled within a reasonable time. Due to a lack of autoignition delay times of methanol at conditions relevant to heavy-duty engines, a large database was created using chemical kinetics calculations. A neural network model was trained with the tabulated data for fast data retrieval. To validate whether the knock integral approach is robust enough to be applied to a wide range of engine sizes, a calibration constant was added to match the knock predictions to experimental data. Its value was calculated for three different engines, a light and heavy-duty SI engine and a large-bore dual-fuel engine. They highlight a remarkable difference in calibration constant across the different engines investigated.

A simple stress-based failure criterion for predicting unfolding failure

Corners of highly curved composite laminates experience unfolding failure when they are loaded under opening bending moments. This work provides a comprehensive experimental test campaign and a detailed stress analysis to gain insight into the different failure mechanisms occurring in curved CFRP laminates made from three different thermoset materials. Two distinct failure mechanisms are observed: firstly, traditional unfolding failure, occurring in unidirectional curved composite laminates exhibiting pure interlaminar delamination associated to the maximum interlaminar stresses in the curved region and, secondly, induced unfolding failure occurring in multi-directional curved composite laminates, where the failure is assumed to be originated from intralaminar matrix cracks which, under the presence of high interlaminar stresses, further propagate as an interlaminar delamination. A simple stress-based failure criterion is proposed to predict the unfolding failure load which provides a fairly good agreement with the experimental results in all cases.

Tuning Modal Behavior of Additively Manufactured Lattice Structures

Abstract Thanks to the increasingly widespread additive manufacturing technology and promising properties, the use of lattice structures (LS) is becoming increasingly frequent. LS allows the components to be designed with tunable stiffness, which can unlock the control of natural frequencies. However, crucial challenges must be faced to integrate LS into the typical design process. In this work, an experimental and numerical study of LS-enabled tuning of natural frequencies in mechanical components are proposed. In a first step, the difficulties arising with the large amount of finite element method (FEM) nodes, that are required to predict LS complex shapes in detail, are overcome by modeling LS with an elastic metamaterial whose stiffness properties are determined through ad hoc finite element analyses. After that, a simplified investigation can be conducted on the modal properties of components with fixed external shape and variable internal LS filling, based on triply periodic minimal surfaces (TPMS) lattices. In those conditions, the parameters of the LS core can be tuned to control and optimize the global modal frequencies of the entire geometry. In addition, the admissible range of frequencies can be estimated. Optimized plates results are validated through an experimental test campaign on additively manufactured specimens made with laser powder bed fusion technology. The samples are hammer-tested with various boundary conditions while laser sensors measure the oscillation data of selected points. Finally, estimated and identified natural frequencies were compared. The described model is suitable to be implemented in an automated tool for designers.

A fault detection strategy for an ePump during EOL tests based on a knowledge-based vibroacoustic tool and supervised machine learning classifiers

This paper presents a methodology for identifying faulty components in an electric pump during the end-of-line test based on accelerations and pressure pulsation data used to train an ensemble learning algorithm based on supervised machine learning classifiers. Despite various quality control measures in pump manufacturing, some out-of-tolerance components can pass through and end up on the assembly line, potentially leading to premature failure or abnormal noise during real-field operation. Because of the high impact, it is very important to put in place actions to mitigate the risk of delivering non-conform units, even if properly working in terms of pressure-flow rate performances. In this paper, an innovative knowledge-based vibroacoustic tool together with a machine learning built-in Python® library have been used to post-process acceleration and pressure pulsations data to generate features, which are then used to train, and test several supervised machine learning algorithms. The ensemble learning algorithm combines the best classifiers to identify healthy electric pump units with high accuracy, achieving above 95% accuracy in an experimental test campaign carried out on eighty electric pumps. Results are compared using principal component analysis for dimensionality reduction, and a sensor sensitivity study is conducted.

Experimental Methods for Measuring the Efficiency of a Molten Salt Central Receiver

In this work, two different methods for measuring the efficiency of central receivers are analyzed by the case of the High Performance Molten Salt II Project (HPMS-II): the continuous power-on method, and the semi-analytical method. The main difference between the two methods is the procedure to calculate the thermal losses of the receiver: on the one hand, the continuous power-on method calculates the thermal losses from the measurement of the absorbed power by the molten salt for different measured incident powers on the receiver. Here, it is assumed that the thermal losses are independent of the incident power if the molten salt temperature is kept constant. On the other hand, the semi-analytical method calculates the thermal losses as the sum of convective and radiative losses, calculated directly from the Newton and Stefan-Boltzmann equations by measuring the temperature of the tube surface, the ambient temperature, and the wind speed. Therefore, the calculation of the thermal losses is independent from one method to another. The procedure of applying these methods during the experimental test campaign of the HPMS-II receiver is detailed in this paper. Additionally, an uncertainty analysis of both methods is conducted to determine the uncertainty expected for the receiver efficiency measurements.

Experimental investigation of multi-burner array with lean lifted spray flames in inline and inclined configurations

Lean combustion in gas turbines garners attention for emissions reduction, yet it faces stability challenges demanding careful design considerations. In this study, a novel CHAIRLIFT combustor concept, which integrates low swirl lean lifted spray flames known for substantial nitrogen oxides emissions reduction, into a Short Helical Combustors (SHC) arrangement, is investigated. A comprehensive experimental test campaign explores key parameters, including staggered arrangement offset, equivalence ratios, and air inlet temperature, to evaluate its performance. The results reveal exceptional stability in low swirl, lifted flames compared to moderate swirl flames with larger inner recirculation zones. The unwanted flow deflection of highly swirled flames in the SHC arrangement is effectively avoided with the investigated low swirl, lifted flames. The study emphasizes the significant influence of fuel droplet evaporation time on flame stability near the flame root under low air inlet temperatures. Furthermore, at high air inlet temperatures, the complex flame stability mechanism in inclined configurations is controlled by various parameters, including outer recirculation zone size, air inlet temperature, and additional vortices generated by pressure differences near the wall. OH∗ chemiluminescence results corroborate these stability mechanisms, showing that at lower temperatures, the flame stabilizes closer to the nozzle exit due to local rich pockets near the shear layer. Conversely, at the same tilt angle, higher air inlet temperatures lead to an increased flame lift-off height due to faster evaporation and enhanced mixing. Exhaust gas analyses confirm the potential of the investigated lean lifted spray flames in a multi-burner arrangement to achieve very low NOx emissions over a wide range of operating conditions for all investigated burner inclinations. These findings may facilitate the future development and optimization of lean combustion technology for aircraft engines.

Corrosion effects on strands of PT bridges

In recent years, partial failures and collapses involving existing Post – Tensioned (PT) bridges highlighted the need for their structural assessment. Most of existing bridges are approaching the end of their nominal life and constitutive materials have undergone, over the decades, relevant degradation phenomena with dangerous consequences at both local and global level. A good knowledge of material properties, structural details and of the actual maintenance condition of the bridge is then required, especially if we consider that hidden defects – i.e. defects that are not visible without specific investigations – can be responsible of the activation of unexpected brittle failures. Corrosion of prestressing steel cables represents one of the most relevant aspect to investigate, being related to phenomena (such as localized pitting or hydrogen embrittlement) that cannot be detected without specific investigation techniques but that are responsible for relevant decrease of the mechanical properties of materials and modification of the failure modality. Predictive models calibrated basing on experimental results, may represent in presence of aggressive environmental conditions may represent an efficient tool for describing corrosion effects on the mechanical properties of strands and evaluating residual performance.The present work shows preliminary results of a wide experimental test campaign executed on corroded steel strands extracted from an existing prestressed concrete bridge with post-tensioned steel cables; hydrogen embrittlement effects are well visible on the mechanical properties of corroded strands. The peculiarity of the work lies in the availability of naturally corroded strands, with well-known external agents (rain, air, etc.) and exposure period. Preliminary results of FEM analyses on models calibrated basing on experimental tests’ results are even presented.

Evaluation of the environmental impact of HCNG light-duty vehicles in the 2020–2050 transition towards the hydrogen economy

As the world intensifies its efforts to reduce the adverse effects of global warming, the shift towards a fully developed hydrogen-based economy is emerging as a core strategy. This transition involves the strategic blending of hydrogen with conventional fossil fuels such as natural gas (HCNG), allowing for adaptation to hydrogen availability. Nevertheless, the environmental impact of HCNG vehicles in realistic scenarios with variable hydrogen content remains unexplored. This study focuses on evaluating the global warming impact of the transition of light-duty passenger cars from CNG to H2 vehicles using HCNG blends from 2020 to 2050 and different realistic scenarios. The results in the present study were obtained through a combination of an experimental testing campaign that allowed obtaining how the performance and emissions of HCNG vehicles change with the H2 content and a life cycle assessment methodology. Based on the findings, the scenario in which hydrogen was mostly produced from SMR-dominant, was found to have the potential to reach and outperform the zero-emission concept due to the utilization of biogas. From the results of this study, the recommended H2 content in HCNG blends that offers low environmental impact while avoiding the overdemand of hydrogen in the short term for the 2020–2030 decade is 25% H2 content, increasing to 50% by 2030, and to 75%–100% during the 2040–2050 decade, thus reaching the transition towards pure-H2 technology that minimizes environmental impact.

Long-Term Shrinkage Measurements on Large-Scale Specimens Exposed to Real Environmental Conditions

This article presents an experimental testing campaign on large-scale concrete specimens with cross-sectional areas of up to 1 m2 and a specimen length of 3 m. The primary goal of the testing campaign was to study the shrinkage behaviour of large-scale specimens exposed to real environmental conditions. Large-scale prismatic concrete specimens were equipped with vibrating wire strain gauges to monitor the strain evolution inside the specimens. To analyse the shrinkage behaviour of the specimens, the thermal strain had to be deducted from the measured strain. To study the influence of seasonal environmental conditions, different specimen production dates (in summer and winter) were examined. The measured shrinkage strains of the large-scale specimens are compared with the results of shrinkage models developed by two engineering entities (fib (Fédération Internationale du Béton) and RILEM (International Union of Laboratories and Experts in Construction, Materials, Systems and Structures)). The comparison shows a poor agreement of the measurements with the models, even though the results from the model for small specimens tested in the laboratory under constant environmental condition agree well with the experimental results. This leads to the conclusion that the poor agreement between the measurements and the shrinkage models must be due to the seasonally changing environmental conditions. The comparison of the results from specimens with different production dates shows that different shrinkage behaviour occurs, especially in the first year of measurements.

Experimental Validation of the Numerical Model for Oil–Gas Separation

The oil and gas sector is important to the global economy because it covers the exploration, production, processing, transportation, and distribution of oil and natural gas resources. Despite constant innovation and development of technologies to improve efficiency, reduce environmental impact, and optimize operations in the gas and oil industry over the last few decades, there is still room to increase the efficiency of the industry’s equipment in order to reduce its carbon footprint. The separation of gas from oil is a critical stage in the technological production chain, and it is carried out using high-performance multi-phase separators to limit greenhouse gas emissions and have a low impact on the environment. In this study, an improved gas–oil separator configuration was established utilizing CFD techniques. Two separator geometry characteristics were studied. Both cases have the same number of subdomains, two porous media, and four fluid zones, but with a difference in the pitch of the cyclone from the inlet subdomain. The streamlines in a cross-plan of the separator and the distribution of the oil volume fraction from the intake to the outlet were two of the numerical results that were shown as numeric outcomes. The validation of these results was performed using an experimental testing campaign that had the purpose of determining the amount of lubricating oil that is discharged together with the compressed gas at the separator outlet.

Damage detection, localization, and quantification for steel cables of post-tensioned bridge decks

The present work aims to provide an in-situ inspection methodology for prestressed concrete bridges with post-tensioned cables (PT bridges). The adoption of non-destructive techniques (NDT), already widely employed in other engineering fields, is proposed, providing reliable information with a relatively low impact on the existing infrastructure. For each of the specific inspection topics (i.e. cables’ layout detection, defect localization and quantification, estimation of residual prestressing force) the proposed investigation procedure was calibrated through a deep experimental test campaign, including both laboratory tests – planned and performed to validate the method and check its efficiency and reliability – and applications to existing viaducts located on the Italian highways.

Characterisation of soiling on glass surfaces and their impact on optical and solar photovoltaic performance

Photovoltaic (PV) module soiling, i.e., the accumulation of soil deposits on the surface of a PV module, directly affects the amount of solar energy received by the PV cells in that module and has also been suggested as a mechanism that can give rise to additional heating, leading to significant power generation losses or even physical degradation, damage and lifetime reduction. Investigations of PV soiling are challenging and limited. We present results from an extensive outdoor experimental testing campaign of soiling, apply detailed characterisation techniques, and consider the resulting losses. Soil from sixty low-iron glass coupons was collected at various tilt angles over a study period of 12 months to capture monthly, seasonal and annual variations. The coupons were exposed to outdoor conditions to mimic the upper surface of PV modules. Transmittance measurements showed that the horizontal coupons experienced the highest degree of soiling. The horizontal wet-season, dry-season and full-year samples experienced a relative transmittance decrease of 62 %, 66 %, and 60 %, respectively, which corresponds to a predicted relative decrease of 62 %, 66 %, and 60 % in electrical power generation. An analysis of the soiling matter using an X-ray diffractometer and a scanning electron microscope showed the presence of particulate matter with diameters <10 μm (PM10), which was the most prevalent in the studied region. The findings of this study lay the groundwork for research into soiling mitigation practices.

The unsteadiness of tip leakage vortex breakdown and its role in rotating instability

The unsteadiness due to tip leakage vortex (TLV) breakdown was studied using a special experimental test campaign in parallel with numerical simulations. The back flow vortex (BFV), an isolated vortex caused by TLV spiral-type breakdown, was found to play a key role in rotating instability (RI). High-speed pressure transducers were used to measure the unsteady pressure field at the casing end wall of the blade in an isolated subsonic compressor rotor, which identified a low-frequency fluctuation at the near stall condition. A single-passage unsteady Reynolds-averaged Navier–Stokes simulation was used to study the evolution of unsteady flow structures, validated by the experimental measurements. Two distinct kinds of periodically unsteady flow were revealed by the simulations. A high-frequency fluctuation corresponding to 1.0 blade pass frequency (BPF) was caused by the spiral-type breakdown of the TLV. The other low-frequency fluctuation corresponding to 0.5BPF was caused by the feedback interaction between the BFV and the blade loading. The BFV was generated by the TLV breakdown, which was separated from the twisted vortex core of the TLV, and it moved downstream along the pressure side of the adjacent blade. A larger sized BFV reduced the local loading of the adjacent blade. The TLV was weakened as a consequence of the reduced loading, resulting in a smaller sized BFV. The blade tip loading was relatively less affected by the small sized BFV rather than the larger sized BFV. Therefore, the blade loading recovered and the size of the BFV increased, repeating the cycle. This feedback mechanism produced a pressure fluctuation with a frequency equal to 0.5BPF, which was closely related to RI.