Load Drop Research Articles

Accuracy and sensibility analysis of strain measurement based on microimages captured by smartphone with a microscope

Strain measurement is an essential part of structural health monitoring (SHM). The objective of the study is to propose a new method to measure strain on the surface of a structure. The speeded-up robust feature (SURF) method was applied to detect and trace feature points in microimages that were obtained using a smartphone with a compact microscope. Subsequently, the average displacement of feature points in microimages was calculated before and after deformation. Finally, the average strain of a certain distance in the structure surface was obtained. An experiment was performed to measure the average strain in an optical fiber of certain length and compare the data with that measured by the fiber Bragg granting (FBG) to verify the accuracy of the proposed method. Additionally, a water drop loading experiment was performed on the optical fiber to test the sensitivity of the proposed method. The results indicated that the strain measured by the smartphone with a compact microscope was in agreement with the FBG data. The error analysis illustrates the maximum error of the data measured by the two methods is 6με, and this can satisfy the requirements of civil engineering. The result of the water drop experiment reveals that the entire process of loading via water drops can be measured by the proposed method, and strain increases with the drops of water. The experimental results verify that the feasibility of the proposed method can satisfy the needs of structural health monitoring for general buildings.

The assessment of impact damage caused by dropped objects on floating offshore structures

Offshore facilities are exposed to the risk of accidental damages caused by fire, explosion, dropped objects, extreme environmental events and vessel collision poses a big threat to the safety and operation. During any lifting work, either from a supply vessel to the installation or from within the installation or plant itself, there is a potential danger when objects are being lifted for a dropped object accident to take place. This paper introduces extensive dropped object analyses applied in the design of Floating Production Storage Offloading (FPSO) offshore units, where non-linear finite element analyses are performed using an explicit LS-DYNA tool. In the structural evaluation, the hull parts such as infill deck, galley, and main lay-down located on poop deck, and cargo deck are taken into account. The dropped objects study is to find out what happens to the FPSO hull structure if the heavy items are dropped. The drop object impact analyses show that even though some structural members were permanently deformed by drop loads, however, there was no failure taken place in accordance with the plastic strain criteria as per NORSOK Code. It is discovered that the pillars supporting the main lay-down area have not been suffered from buckling failure through examined reaction forces. Further, the impact resistance of a deck depends on the plate thickness and the size and spacing of the supporting stringers.

Detection of CFRP-concrete interfacial debonding using active microwave thermography

Active microwave thermography (AMT), a thermographic technique that utilizes a microwave-based thermal excitation, is proposed as an efficient technique for non-contact, real-time inspection of embedded flaws. This study examines the use of AMT to detect interfacial debonding of the carbon fiber reinforced polymer (CFRP)-concrete interface. CFRP-concrete interfacial damage is caused by external mechanical loading and monitored under AMT. CFRP strips bonded to concrete prisms are tested in direct shear to initiate debonding. AMT is used to monitor the CFRP surface thermal profile in an attempt to detect and monitor interfacial damage. Correlations between the mechanical response (namely, applied load vs. composite displacement relative to the substrate, i.e., slip) and AMT results (namely, temporal CFRP thermal response) are found. High thermal contrast, TC, defined as the CFRP surface thermal response caused by loading, is observed where interfacial debonding initiates and propagates along the bonded length. An increase in the TC slope occurs when a load drop occurs, which indicates local debonding occurrence or mobilization. At different load levels, the interfacial slip and surface temperature distributions along the bonded length show similar trends. These correlations indicate that initiation and propagation of CFRP-concrete interfacial damage can be monitored by the AMT technique.

The Role of Chrysoperla carnea (Steph.) (Neuroptera: Chrysopidae) as a Potential Dispersive Agent of Noctuid Baculoviruses.

Simple SummaryBaculoviruses (BV) infect several lepidopteran pests of economic importance, such as the beet armyworm Spodoptera exigua. The joint use of microbiological and macrobiological strategies may improve the efficacy of control. Laboratory bioassays were developed to evaluate the interactions between two BVs: the multiple nucleopolyhedroviruses of S. exigua (SeMNPV) and Autographa californica (AcMNPV), and the predator Chrysoperla carnea. The excretion products of the predator’s larvae (drops) and adults (meconia) were microscopically examined after the ingestion of BV-infected S. exigua larvae. For both types of excreta and BVs, viral occlusion bodies (OBs) (resistance forms) were observed. These OBs were infective to healthy S. exigua larvae when applied in water suspension and in direct deposition. The virulence of meconia was higher in suspensions (higher viral load), while larval drops were more virulent in direct application due to their liquid nature and their easiness of consumption. The fitness of C. carnea was slightly affected by the consumption of both BV-infected prey. No preference was shown between healthy and BV-infected S. exigua, and both were preferred vs. the aphid Macrosiphum euphorbiae. Our findings present C. carnea, and particularly its larvae, as a promissory candidate for BV dispersion in the field.Baculoviruses (BV) are highly effective against lepidopteran pests of economic importance such as Spodoptera exigua. The combined use of entomopathogens and macrobiological control agents requires the study of their relationships. Laboratory bioassays were developed to evaluate the interactions between the multiple nucleopolyhedroviruses of S. exigua (SeMNPV) and Autographa californica (AcMNPV), and the predator Chrysoperla carnea. The microscopic examination of predator’s excreta (larval drops and meconia) after the ingestion of BV-infected S. exigua revealed the presence of viral occlusion bodies (OBs). The reinfection of S. exigua larvae with BVs-contaminated excreta by using OBs water suspensions or by direct application both yielded high mortality values but different speed-of-kill results. Meconia killed before in suspensions due to their higher viral load and larval excretion drops did so in direct application due to their liquid nature and their easiness of consumption. The prey-mediated ingestion of SeMNPV and AcMNPV triggered slight effects in C. carnea, which were probably derived from the food nutritional quality. Chrysoperla carnea larvae did not discriminate between healthy and BV-infected S. exigua, while a preference was shown for S. exigua (healthy or infected) vs. Macrosiphum euphorbiae. Our findings present C. carnea, and particularly its larvae, as a promissory candidate for BV dispersion in the field.

Experimental issues in the instrumented 3 point bending VDA238-100 test

The instrumented 3-point bending test according to VDA238-100 test standard is increasingly used within the steel and automotive industry. Originally developed for aluminum hemming characterization, this bending test has been shown to be also relevant for local formability and crash foldability assessment originally of press-hardened steel grades and more recently for newly developed advanced and ultra high strength AHSS/UHSS steels grades. This instrumented bending test delivers bending load vs. bending angle curves. It is commonly assumed that material failure shortly happens beyond maximum load after a 30N load drop. The bending angle at maximum force aFmax characterizes then the bendability of the investigated material. The assumption maximum force = bending crack initiation, while being true for press-hardened grades, is in too many case not valid for steel grades with tensile strength ⩽1200MPa and cannot be universally trusted. An alternative approach is presented using passive acoustic emission sensors placed in the vicinity of the bending punch. The interpretation of such acoustic data is however quite subjective and still in trial status. Redundant crack detection systems based on load, acoustic as well as optical measurements may have to be considered together for increasing crack detection reliability within the VDA238-100 bending test specification.

MEMS-based in-situ tensile experiments designed to arrest catastrophic failure in brittle nanomaterials

Quantitative characterization of mechanical properties of many nano- or micro-scaled materials is of crucial importance for many technological applications. Among various experimental methods, the in-situ nanomechanical tensile testing is of particular significance due to its capability of direct observation of mechanical behavior. Especially, the tensile loading mode enabling the precise displacement control is desirable for brittle nanomaterials that often suffer from the catastrophic failure by mechanical instability. In this study, we developed the MEMS-based nanomechanical tensile device optimized for stable displacement control even in the presence of the rapid reduction of sample stiffness. The MEMS device is designed to stabilize the motion of the actuating rod in the testing equipment via the high stiffness of springs and the large mass of the movable part. To verify the performance of the device, we conducted tensile testing on the pre-notched metallic glass samples and successfully observed fast load drops during crack propagation.

Impact analysis of COVID-19 responses on energy grid dynamics in Europe

When COVID-19 pandemic spread in Europe, governments imposed unprecedented confinement measures with mostly unknown repercussions on contemporary societies. In some cases, a considerable drop in energy consumption was observed, anticipating a scenario of sizable low-cost energy generation, from renewable sources, expected only for years later. In this paper, the impact of governmental restrictions on electrical load, generation and transmission was investigated in 16 European countries. Using the indices provided by the Oxford COVID-19 Government Response Tracker, precise restriction types were found to correlate with the load drop. Then the European grid was analysed to assess how the load drop was balanced by the change in generation and transmission patterns. The same restriction period from 2020 was compared to previous years, accounting for yearly variability with ad hoc statistical technique. As a result, generation was found to be heavily impacted in most countries with significant load drop. Overall, generation from nuclear, and fossil coal and gas sources was reduced, in favour of renewables and, in some countries, fossil gas. Moreover, intermittent renewables generation increased in most countries without indicating an exceptional amount of curtailments. Finally, the European grid helped balance those changes with an increase in both energy exports and imports, with some net exporting countries becoming net importers, notably Germany, and vice versa. Together, these findings show the far reaching implications of the COVID-19 crisis, and contribute to the understanding and planning of higher renewables share scenarios, which will become more prevalent in the battle against climate change.

Effect of individual phase properties and volume fractions on the strain partitioning, deformation localization and tensile properties of DP steels

Deformation band localization modes, uniform tensile strength, and uniform elongation of Ferrite-Martensite Dual-Phase (DP) steels are analyzed by finite element (FE) study. Treating the microstructure inhomogeneity as the sole cause of imperfection, failure initiation is predicted as the natural fallout of plastic instability caused by load drop because of localized plastic strain in the Representative Volume Element (RVE) during straining. Strain partitioning between two phases (ferrite matrix and martensite island) are investigated on RVEs, and it reveals that the increase of martensite yield stress decreases the plastic deformation and increases the stress state in martensite. Whereas, a decrease in martensite island volume fraction (Vm) results in the reduction of plastic deformation and stress state in the island. Studies are then carried out to investigate the effects of the ferrite-martensite flow properties and martensite volume fraction on the macroscopic tensile deformation behavior and band localization of DP steels. Micromechanical based FE simulation results emphasize that an increase in initial yield strength and volume fraction of martensite increases the ultimate tensile stress (UTS) with the decrease in uniform elongation. Similarly, as the hardening rate of ferrite increases, it increases the ultimate tensile stress (UTS) and uniform elongation. Additionally, deformation band localization modes alter from inclined to perpendicular to the loading axis with an increase in martensite volume fraction and initial yield strength of martensite. The knowledge of this work can be used to design DP steels with desired mechanical properties.

New Methodologies for Fracture Detection of Automotive Steels in Tight Radius Bending: Application to the VDA 238–100 V-Bend Test

The VDA 238–100 tight radius V-bend test can be used to efficiently characterize the bendability and fracture limits of sheet metals in severe plane strain bending. Material performance in plane strain bending is critical for the selection of advanced high strength steels for energy absorbing structural components. The detection of failure based upon a reduction in the punch force can lead to erroneous predictions of failure for ductile or thin gage alloys in the VDA 238–100 test. New failure criteria were proposed and evaluated across a range of automotive steels. Four detection methods in the V-bend test were evaluated based upon the load drop, bending moment, novel stress metric and the strain rate for seven steels with strength levels from 270 to 1500 MPa. The appropriate failure threshold was identified from visual inspection of the surface during bending. The vertical punch force will decrease as a consequence of the mechanics in the V-bend test at intermediate bend angles even without fracture. The novel stress-based metric accounts for sheet thinning and could successfully identify “false positives” and punch lift-off when considering the strain-rate evolution. Failure detection using the VDA load threshold method may significantly under-report the bend performance of alloys with intermediate-to-high bendability or thin gauges. The proposed stress-based metric can reliably detect fracture for bend angles in excess of 160° and be readily calculated using the existing data. The VDA load threshold for failure can work well for materials that exhibit significant cracking.

Interplay between oral immunity in HIV and the microbiome

This Basic Science Workshop addressed the oral microbiome. At the 7th World Workshop on Oral Health & Disease in HIV/AIDS in India in 2014, some aspects of the human microbiome were discussed, and research questions formulated. Since that time, there have been major advances in technology, which have stimulated a number of publications on many aspects of the human microbiome, including the oral cavity. This workshop aimed to summarize current understanding of the "normal" microbiome of the oral cavity compared to that during HIV infection, and how oral immune factors and other clinical variables alter or control the oral microbiome. An important question is whether successful treatment with anti-retroviral therapy, which leads to a significant drop in viral loads and immune reconstitution, is associated with any change or recovery of the oral microbiome. Additionally, the workshop addressed the issue of which parameters are most appropriate/correct to evaluate the oral microbiome and how clinically relevant are shifts/changes in the oral microbiome. The workshop evaluated current knowledge in five research areas related to five basic questions and identified further topics where further research is required.

Dynamics of high penetration photovoltaic systems in distribution circuits with legacy voltage regulation devices

Concerns for criteria pollutant emissions and air quality, as well as greenhouse gas emissions, have resulted in stringent energy and environmental rules and regulations mandating deployment of renewable resources. Moreover, increased frequency of extreme weather events highlighted the need for increased reliability and resiliency of the grid further encouraging deployment of distributed energy resources. This has resulted in an increasing deployment of solar PV in the distribution system. While many studies focus on analyzing the impact of increased penetration of PV on smart circuits or systems with upgraded infrastructure, it is necessary to assess impacts on existing circuits with legacy devices. In this study, the impacts of high penetration of PV are investigated for two distribution circuits (one residential and one commercial) located in northern California, equipped with legacy voltage regulation devices including on-load tap changer (OLTC) transformers and switched capacitor banks.The dynamics of circuit operation and bus voltage profiles are studied by developing time-resolved three-phase balanced feeder models of the two circuits. Using connectivity and load demand measurements provided by the utility, the models are validated and calibrated to the point of the substation. In order to help generalize the results associated with the two circuits, a set of circuit design metrics are developed to characterize the distribution of the load demand and generation, load center (LC) and generation center (GC). The load center and generation center metrics are weighted averages of the total consumed and total produced bus energy relative to the distance from the substation.Various scenarios are simulated in order to quantify generation limits necessary to conform to various standards including ANSI C84.1 voltage standards while maintaining reliable circuit operations. In these scenarios, location of the PV installation as well as PV penetration (from baseline to 100%) are varied. Simulation results indicate that high PV penetrations have a direct impact on OLTC transformer operation but only marginal impact on capacitor switching. Tap operation is found to increase approximately linearly with PV penetration for both of the circuits and specific Load Drop Compensation (LDC) controller settings greatly affect the sensitivity of OLTC operation to PV penetration. It is also concluded that not only the location of PV installation relative to loads and substation affects the performance, the metrics developed are a powerful tool to describe high PV circuits and to help utilities better plan for deployment of PV in their distribution network.

Failure Analysis of Silane-Treated Kevlar-Reinforced Nano-silica-Toughened Epoxy Composite in Laminar Shear Strength, Drop Load Impact and Drilling Process

In this research, the role of silane surface modification on Kevlar fiber and nano-silica and their failure analysis on inter-laminar shear strength and drilling process were studied. The main objective of this research is to explicate the importance of silane surface modification on the reinforcements and their failure effects on proposed properties. The Kevlar fiber and nano-silica were surface-treated using 3-aminopropyltrimethoxysilane using aqueous solution method. The composites were prepared using hand layup technique followed by post-curing at 120 °C. The inter-laminar shear strength results show that the silane-surface-modified fiber and filler in epoxy composite give the highest strength of 32 MPa for EKS2. The highest drop load impact energy of 16.3 J was observed for surface-modified composite designation EKS2. Similarly, the surface-modified epoxy composite designations show highest dimensional stability than as-received designations in drilling process. There are no fiber pullout and edge damage observed in optical microscopy images after drilling process. These high shear strength, high energy absorption and high de-lamination-resisted Kevlar-epoxy composites could be used in defense, armor equipment, automobile bumpers and small aircraft manufacturing applications.

Fabrication and Characterization of Acrylonitrile Butadiene Rubber and Stitched E-Glass Fibre Tailored Nano-Silica Epoxy Resin Composite

In this research, the role of acrylonitrile butadiene rubber (ABR) and nano-silica along with stitched E-glass fibre in epoxy composite was investigated. The main objective of this present study is how the additions of ABR and nano-silica particle influences in the mechanical, drop load impact and fracture toughness properties of glass-epoxy composite. The layering of rubber sheet for improving the reinforcing effect is a novel approach in reinforced plastic. The composites were prepared using various stacking sequence of ABR and E-glass fibre with nano-silica toughened epoxy resin. The composites were characterized using ASTM standards. According to mechanical properties the composite designation FAF2 symmetric arrangement gives better overall (rank of 97) properties. Similarly, the composite designation AFA2 gives very higher penetration resistance against the fast moving impactor. The fracture toughness behaviour of the composite shows higher energy release rate of 3.8 MJ/m2 and fracture toughness of 22 MPa for 3 vol.% of nano-silica particle dispersed FAF epoxy composite. The SEM micrographs show improved adhesion of 3 vol.% nano-silica with fibre and ABR in composites. The penetration improved rubber based epoxy composites could be used in armour based device, automobile body parts and domestic product manufacturing industries.

Comprehensive analysis of the thermohydraulic performance of cooling networks subject to fouling and undergoing retrofit projects

The aim of this paper is to develop guidelines for the placing of new coolers in cooling systems subject to retrofit. The effects of the accumulation of scale on the flow system are considered. A methodology to assess the interconnected effect of local fluid velocity and fouling deposition is developed. The local average fluid velocity depends on the water flow rate distribution across the piping network. The methodology has four main calculation components: a) the determination of the flow rate distribution across the piping network, b) the prediction of fouling deposition, c) determination of the hydraulic changes and the effect on fouling brought about by the placing of new exchangers into an existing structure, and d) the calculation of the total cooling load and pressure drop of the system. The set of disturbances introduced to the system through fouling and the incorporation of new coolers, create network responses that eventually influence the cooling capacity and the pressure drop. In this work, these interactions are analysed using two case studies. The results indicate that, from the thermal point of view, the incorporation of new heat exchangers is recommended in series. The limit is the point where the increase of the total pressure drop causes a reduction in the overall volumetric flow rate. New coolers added in parallel create a reduction of pressure drop and an increase in the overall water flow rate; however, this increase is not enough to counteract the reduction of fluid velocity and heat capacity removal.

Experimental demonstration of the in-situ effect under transverse shear

Failure of composite laminates, in load cases where transverse shear prevail, involves shear cracks and delaminations, and yet it is unclear which damage mechanism triggers the other or how it depends on ply-thickness. Combining interrupted interlaminar shear strength tests with X-ray tomography inspections, we compared the damage sequence of [45°/0°/-45°/90°]ns short-beam specimens manufactured with standard- (n=2) or thin-ply (n=4) non-crimp fabrics (fibre areal weights of 134 and 67 gsm per ply). Failure manifested as a load drop in the force-displacement curve. In both materials, we associated the onset of instability to a shear crack tunnelling across the central 902° ply-cluster. The intersection of this crack with the ones developing in the adjacent layers induced a delamination which, in turn, activated the load drop. A 3D elasto-plastic model predicted that, for the same applied load, the ply-cluster of both laminates would display a similar maximum principal stress distribution. However, the thin-ply samples improved the interlaminar shear strength by 34%, evidencing the so called in-situ effect: the resistance to matrix cracking under transverse shear (τ23 in the local coordinates of the 90° plies) increases when ply-thickness is reduced.

In situ characterization of trans-laminar fracture toughness using X-ray Computed Tomography

The change in the critical strain energy release rate as damage evolves, known as the R-curve, is of crucial importance to the understanding of fracture behaviour. The examination of damage evolution ahead of the crack tip in order to determine accurately the crack increment is key for the determination of the R-curve. Conventional in situ methods such as optical measurements only examine the specimen surfaces. X-ray Computed Tomography (CT) offers satisfactory image quality, but conventional CT scanning requires the removal of the specimens from the test machine. If no dye penetrant is used, the specimens can be re-loaded, but some important information will be missing such as the early load drops corresponding to damage initiation. If dye penetrant is used, the specimens can no longer be re-tested. In contrast, in situ CT scanning can capture the detailed damage states ply-by-ply while the specimen is loaded and diminish the need for multiple specimens. In situ characterization of trans-laminar fracture toughness of composites using CT has not been attempted in the past. It has been proven successful in this research, and shown that a partial R-curve can be constructed with a single Extended Single-Edge-notch Tension (ESET) specimen.

Mechanical, Low Velocity Impact, Fatigue and Tribology Behaviour of Silane Grafted Aramid Fibre and Nano-silica Toughened Epoxy Composite

This investigation deals the effects of adding silane-modified nano-silica particle in aramid fibre (Kevlar-49) toughened epoxy resin composite. The principal aim of this research work is to reveal the importance of adding nano-silica particle in various mechanical properties of aramid fibre-reinforced epoxy resin hybrid composite. The aramid fibre and nano-silica particle were surface-treated using 3-Aminopropyltrimethoxysilane (APTMS) via acid hydrolysis process. The tensile and flexural results revealed that the addition of aramide fibre into nano-silica toughened epoxy resin hybrid composite gives improved tensile and flexural strength of 102 MPa and 135 MPa. Similarly, the Izod impact strength of fibre-reinforced nano-silica (1 vol.%) toughened epoxy resin composite gives energy absorption up to 6 J. The drop load impact penetration of composite designation N3 shows very limited penetration than other composite designations. The highest fatigue life of 16,391 cycles was observed for composite designation N3, which contain1 vol.% of nano-silica. Similarly, the composite contains 2 vol.% of nano-silica gives a very lower specific wear rate and coefficient of friction (COF). This high modulus, stiffness, wear resistance and fatigue life improved hybrid composites could be used in automobile power transmission gears, wind turbine blades, blowers, domestic equipment and farm-related machinery.

Strength characterization of caryota urens fibre and aluminium 2024-T3 foil multi-stacking sequenced SiC-toughened epoxy structural composite

High toughness and high-impact damage resistance fibre-metal hybrid laminate epoxy composites were prepared and characterized. In this present research, a hybrid fibre-metal laminate was reinforced into SiC-toughened epoxy resin for making high performance structural material for automobile and aircraft applications. Novel natural fibre caryota urens and silicon carbide (SiC) particles were surface-treated using 3-aminopropyltriethoxysilane (APTES) whereas the aluminium foil was sandblasted. The hybrid fibre-metal laminate with different stacking sequenced epoxy composites were prepared using vacuum bag moulding followed by post curing. A highest strength factor of 97 is observed for composite designation CAC1, which contains 0.5 vol.% of SiC. The drop load impact toughness of ACA1 composite gives the highest energy absorption of 20.6 J. Similarly, the CAC1 composite designation gives fracture toughness of 32.1 MPa. $$ \sqrt{\mathrm{m}} $$ and energy release rate of 1.557 mJ/m2. The scanning electron microscope images revealed highly reacted phase of surface-treated reinforcements with epoxy resin matrix.

Quasi-static indentation response of core-shell particle reinforced novel NCCF/Elium® composites at different feed rates

In the current research, the static indentation properties of composite laminates toughened by the addition of core-shell (C/SH) particles at the interfaces of non-crimp carbon fibre (NCCF)/Elium® composite laminate is investigated. NCCF/Elium® composite exhibited improved static indentation performance with an increase in the feed rate. There is a 19.6% and 13.5% increase in peak load with no particle reinforcement and 5% C/SH respectively when the feed rate was increased from 1 mm/min to 10 mm/min. Also, the 27% drop in the intensity of the major load drop was noticed when the interply region was toughened by the addition of 5% of the C/SH particles. Microscopic observations also showed reduced delamination with the increase of C/SH particles. The progressive failure was reduced due to increased energy absorption and delayed onset of fibre breakage and delamination.

Generalized separator failure criteria for internal short circuit of lithium-ion battery

To enable the understanding of the internal short circuit mechanism triggered by separator failure, mechanical indentation loadings are designed to create the deformation of the separator in a precisely controllable way. Herein, two characteristic short-circuit types are observed in anode-separator-cathode stack upon mechanical abusive loading, i.e., rapid and gentle voltage drop. Through the ex-situ experiment, the rapid voltage drop is due to the direct contact between cathode and anode as a result of separator fracture, while the gentle voltage drop is related to the flattening of the separator with the absence of its function to isolate electron transfer. The developed detailed numerical models, considering the failure of anode and cathode and the anisotropy of separator, can well describe the mechanical responses of components and stack. Thanks to the numerical computation model and computation, we establish and validate the generalized short-circuit criteria for the two representative failure modes based on the volumetric strain and equivalent strain of separator. Results provide a powerful and generalized tool aiming for the design of next-generation separator technology, enabling a more fundamental and effective way for future ISC detection, monitoring, and evaluation which can be embedded within the battery management system.