Hail Impact Research Articles

Structural performance enhancement: bio-inspired honeycomb solutions for high-velocity hail impact challenges

Structural performance enhancement: bio-inspired honeycomb solutions for high-velocity hail impact challenges

Dynamic response and safety performance of composite-laminated heliostat under hail impact

ABSTRACT Areas rich in solar energy are prone to strong convective weather, leading to severe hail disasters, which makes heliostats under the threaten of hail impacts. An evaluation model of composite laminated heliostat under hail impacting is established and validated. Subsequently, the effect of interlayer type and thickness ratio on the dynamic response and safety assessment of composite laminated heliostats impacted by hail are investigated. Additionally, the velocity thresholds for hail terminal velocity of composite laminated heliostats with a thickness range of 2–4 mm, based on the optimal thickness ratio, are studied. The results indicate that the maximum principal stress value of the composite laminated heliostat remains similar to that of the single-layer heliostat when the interlayer types are SentryGlas Plus (SGP) and Polyvinyl Butyral (PVB). The maximum principal stresses of single-layer heliostats with thicknesses of 2-4 mm are 2.92, 1.50, and 1.35 times, compared to the first-layer glass of composite laminated heliostat with the same thickness under the optimal thickness ratio, which indicates that the hail resistance of the composite laminated heliostat is superior to that of the single-layer heliostat. The findings offer the guidance for the hail resistance of composite laminated heliostat under hail impact.

Fast fracture in toughened glass when impacted randomly by Ice

Modelling the triggering of fracture at a pre-existing flaw is an evolving method of predicting ultimate failure in glass. This fracture mechanics approach of modelling has been shown to give more reliable predictions than a calibrated probabilistic distribution model (as is commonly adopted) when dealing with hail impact which is highly transient in nature. The dynamic stress intensity factor controlling fast crack growth is sensitive to the complex stress state surrounding the critical flaw. Finite element simulations of localised stresses in 3D could incur high computation cost which is compounded by the need to repeat computations until convergence and to simulate multiple strikes in emulating a storm scenario. In this study, closed-form expressions were developed to waive away the need of any simulations. With hail impact, boundary conditions of the glass panel need not be factored into the modelling, as the highly transient stresses are wave controlled. Input parameters are the thickness and level of prestress in glass; offset of position of strike from the known crack and its depth; and the size, velocity, and temperature of the ice impactor. Results from 40 test scenarios involving 5 offset distances, 3 crack depths, 2 glass thicknesses, and 2 sizes of ice were used to validate the prediction, and to reveal the sensitivity of the outcome of the impact to changes in the impact position relative to the known crack.

Towards fiber-reinforced front-sheets for lightweight PV modules in VIPV

Novel approaches in the field of photovoltaics, such as building or vehicle integration require investigations of lightweight PV module concepts [1]. This research proposes and evaluates a lightweight PV module concept using glass fiber-reinforced polymers (GFRP) based on epoxy composites within the module stack. The usage of GFRP as front material as proposed in this work, reduces weight by 44–74 % compared to conventional glass-back sheet modules. We show results that with the proposed module stack hail impact resistant module can be built with small and large size avoiding any cell cracks after impact. Additionally, modules with GFRP front layer withstand thermal cycling tests with low power losses ranging from −0.9 % to −1.1 % at Pmpp depending on the individual GFRP layer. We also show results of cut susceptibility tests with an increased performance compared to modules with a polymeric front layer. Development topics remain as shown by damp-heat and UV irradiation testing, were an optimization of the module stack still needs to be performed.

Experimental study on the influence of turbulence on hail impacts

Hailstorms, characterized by their intensity, are often accompanied by strong winds and heavy rain, posing significant destructive potential. Data indicate that the economic losses caused by hail to buildings, particularly solar panels, have been increasing annually. However, research on the hail resistance of photovoltaic panels has predominantly focused on the isolated effects of hail impacts and wind loads, neglecting the coupling effects between wind and hail. In this study, a device was designed to couple both wind and hail. The effects of turbulence, hail size, and velocity on hail impact behavior were systematically studied and quantified. A predictive formula for the peak load of hail impact on structures was established. The results indicate that the impact of turbulence on hail is significant. When turbulence intensity varies with hail velocity, hail impact force increases as turbulence decreases and hail velocity increases. When both turbulence and hail diameter vary, the impact force of smaller hailstones shows less variation with increasing turbulence. According to variance analysis, hail velocity is the most significant factor affecting hail impact, followed by hail diameter and finally turbulence. The regression equation is given by F=-0.624Iu+5116.25D+7.85Vhail-259.709\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$F = - 0.624I_{{\ ext{u}}} + 5116.25D + 7.85V_{hail} - 259.709$$\\end{document}, where F\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$F$$\\end{document} represents the peak impact force in Newtons (N), Iu\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$I_{{\ ext{u}}}$$\\end{document} denotes the turbulence intensity, D\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$D$$\\end{document} is the hail diameter in meters (m), and Vhail\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$V_{hail}$$\\end{document} is the hail velocity in meters per second (m/s).

Encapsulation strategies for mechanical impact and damp heat reliability improvement of lightweight photovoltaic modules towards vehicle-integrated applications

Lightweight modules are essential for next-generation vehicle-integrated photovoltaic (VIPV) applications, such as solar-powered cars, allowing integration of solar cells beyond the roof, and on the hood, boot and body panels, and thereby extending the driving range. However, the lightweight module's reliability and corresponding degradation mechanisms under various environmental stresses are less researched. In this work, we investigate interconnection and encapsulation strategies to improve reliability against damp heat and mechanical impact. We fabricated lightweight mini modules, weighing around 3.45 kg/m2, and conducted hail impact and damp heat tests. These tests result in different failures, such as cracks in the solar cell, module delamination, and microcracks in the backsheet. By carrying out failure mechanism analysis and altering the fiber reinforcement in backsheet and encapsulation materials, we can increase resilience to these failure modes, thus providing guidance for the design of lightweight PV modules for next-generation VIPV.

Mechanical responses and damage characteristics of the high-velocity impact of ice projectiles on foam sandwich structure

The integration of composite sandwich structures in aircraft design necessitates consideration of hail impacts within aerospace applications. This investigates the dynamic response and damage characteristics of a carbon fibre/PMI foam sandwich structure under hail impact through both experimental and numerical simulation methods. These methods analyse the impact velocity, fibre panel thickness, and angle of incidence of the ice projectiles. The study establishes relationships among various parameters such as ice projectile impact force, foam absorption energy, and target plate deformation in relation to the impact velocity and angle of incidence. The damage sustained by the carbon fibre/PMI foam sandwich (CPS) structure due to ice projectile impact was systematically categorized and examined. Additionally, the effects of normal and tangential impact velocities on the target plate's dynamic response during oblique impacts were investigated. This research serves as a valuable reference for understanding the dynamic response and damage characteristics of composite foam sandwich structures subjected to ice projectile impacts, With a focus on the carbon fibre/PMI foam sandwich structure.

Bioinspired honeycomb sandwich structures for enhanced hail impact resistance

The study explores the mechanical behavior of bioinspired honeycomb sandwich structures against hail impact using Ls-Dyna. The hail model, based on experimental values, is created with smoothed particle hydrodynamics. The force-time graph aligns with the peak value from the impact test on a rigid bar, showing good agreement with literature. The sandwich model, impacted by a hemispherical-nosed impactor, exhibits post-impact damage images and collapse in the z-axis consistent with experimental results. Diversified honeycomb cell profiles include wavy, spider web, bamboo, and combinations. When subjected to hail impact, the wavy model excels in sEA, spider web-bamboo in specific deformation, and bamboo in sPCF.

The relationship between repeated impacts and CAI strength of sandwich structure considering different impactor shape in individual impact

Sandwich structures are susceptible to repeated impact loads, and each individual impact is not nearly identical to the previous one, especially for repeated impacts under different impactor shapes such as hail impact. Therefore, the repeated impact behavior using different impactor shape in individual impact of polymethacrylimide (PMI) foam sandwich structure is studied and discussed through experiments and finite element (FE) simulations in this paper. The representative mechanical characteristics such as impact responses, damage modes, and energy absorption are investigated until penetration occurs, and the mechanism of impact damage accumulation between impact events with different impactor shapes is revealed. Besides, the compression after impact (CAI) strength is utilized to assess the residual strength of sandwich structure under repeated impacts. It indicates when the contact area between the specimen and impactor is larger, it can result in a higher impact force, a shorter contact duration, and potentially reduce the extent of damage. The matrix damage is the main damage mode, and the proportions of matrix tension and compression are nearly constant, with a ratio of approximately 2:1. In addition, the proportion of the impact energy absorbed by foam core increases as the number of impacts increases. When the impact energy is low, the CAI strength is sensitive to the number of impacts, the shape of impactor, and the sequence of impactors, but the similar phenomenon does not occur at higher impact energy. The present study provided a series of experimental and numerical results, which could be utilized as design reference guidance in the designing of composite sandwich structures.

Radar and environment-based hail damage estimates using machine learning

Abstract. Large hail events are typically infrequent, with significant time gaps between occurrences at specific locations. However, when these events do happen, they can cause rapid and substantial economic losses within a matter of minutes. Therefore, it is crucial to have the ability to accurately observe and understand hail phenomena to improve the mitigation of this impact. While in situ observations are accurate, they are limited in number for an individual storm. Weather radars, on the other hand, provide a larger observation footprint, but current radar-derived hail size estimates exhibit low accuracy due to horizontal advection of hailstones as they fall, the variability of hail size distributions (HSDs), complex scattering and attenuation, and mixed hydrometeor types. In this paper, we propose a new radar-derived hail product developed using a large dataset of hail damage insurance claims and radar observations. We use these datasets coupled with environmental information to calculate a hail damage estimate (HDE) using a deep neural network approach aiming to quantify hail impact, with a critical success index of 0.88 and a coefficient of determination against observed damage of 0.79. Furthermore, we compared HDE to a popular hail size product (MESH), allowing us to identify meteorological conditions that are associated with biases on MESH. Environments with relatively low specific humidity, high CAPE and CIN, low wind speeds aloft, and southerly winds at the ground are associated with a negative MESH bias, potentially due to differences in HSD, hail hardness, or mixed hydrometeors. In contrast, environments with low CAPE, high CIN, and relatively high specific humidity aloft are associated with a positive MESH bias.

Experimental and numerical investigation on high-velocity hail impact response of TC4 titanium alloy plates

This work studied the dynamic response of hail impacting on TC4 titanium alloy plates under different influence factors. Experiments were performed according to China Civil Aviation Regulations Airworthiness Standards. The damage to the plate was recorded by in-situ cameras. The experimental results indicate that the greater the hail velocity, the more severe the damage to the titanium alloy plate. In the simulation, Smoothed Particle Hydrodynamics (SPH) method was used to model the hail. The reliability of numerical model was verified by the comparison with the test results of hail impact response. The numerical results show that the deformation of the plate increases as the impact angle and hail diameter increases. Moreover, the changes in impact angle and position will both alter the displacement and strain distribution within the plate. Through comparative analysis of the impact velocity, hail diameter, impact angle, and impact position on the impact force peak, plastic strain energy, and maximum kinetic energy of the plate, it is found that changes of hail diameter and velocity have great effect on the response of titanium alloy plate, and the impact position has little effect on it. There is a power-law relationship between the hail impact peak force and the hail velocity with an index of 1.912.

Dynamic Response Characteristics of Heliostat Impacted by Continuous Hails

The Tibet Plateau is an area with abundant solar energy resources. However, it is also a location where severe thunderstorm disasters, for instance hail, frequently occur. In this paper, the dynamic response of the heliostat under impact by continuous hails was investigated. The effects of time interval of hail impact, hail diameter, impact position, as well as random multi-hail impact and random multi-hail distribution density were studied on the dynamic failure assessment of heliostat under continuous hail impacts. Results indicate that the continuous impact of hail on the same position of the heliostat causes a superposition effect on the heliostat. In case where larger-diameter hail initially impacts the heliostat, followed by smaller-diameter hail impact, the maximum principal stress in heliostat reaches its peak after the first hail impact and then steadily declines. When the heliostat is hit first by small-diameter hail followed by larger-diameter hail, it causes more damage to the heliostat compared to the case when the impact sequence is switched. The distance between continuous hail impacts reduces the increase of the maximum principal stress of the heliostat while increases the displacement value at the impact point of the heliostat. When the hail density increases by twice, the maximum principal stress increases significantly. The larger the hail distribution density, the smaller the stress concentration area, and then it gradually expands to both ends over time.

Delamination link-ups in composite laminates due to multiple hail impacts

Damages to aircraft fuselages by ice impactors are categorized as barely visible impact damage (BVID). As the application of composite laminates in manufacturing aircraft fuselage is increasing rapidly, studying hail impact on composite laminates seems crucial. Investigation of variation of delamination area and link-up area for different impact scenarios between ice and carbon fibre prepreg composite plates is the main goal of this study. Link-up refers to joining of delaminated areas created by separate impacts at relatively close impact locations. To this aim, multiple impacts at 1 and up to 6 impact locations and with different impactor energies were simulated using SPH formulation, and delamination areas were quantified. The results showed that as the spacing L between two impact locations increases from 0 to 4R (where R denotes the impactor radius), the total delamination area first shows an increase up to a peak point (usually at R<L<2R) after which it shows a large drop, and after L≈2R, the total delamination area level remains almost constant. The large drop is related to disappearance of the link-up phenomenon beyond a certain spacing. Moreover, it was observed that increasing the number of impact locations increases the delamination area almost linearly. As for the impactor energy influence, the results showed that as the impact energy increases, the threshold spacing for link-up increases. Moreover, for the case of impact at two locations and constant total energy level, two impactors with identical energy level lead to higher delamination area as compared to impactors with non-identical energy levels.

Experimental and numerical study on the high-velocity hail impact performance of carbon fiber aluminum alloy laminates

The experiment and finite element method (FEM) simulation of high-velocity hail impact on carbon fiber reinforced aluminum alloy laminates (CARALL) were carried out in this paper. CARALL were prepared via an autoclave process after surface anodizing. The properties of the specimens were verified by mechanical properties testing. The light gas gun was employed to conduct the hail impact tests with different impact velocities, impact angles and ply sequences. The surface damage, displacement of the impact center and deformation depth in different test schemes were compared. The FEM model of the high-velocity impact of hail on CARALL was established using ABAQUS/Explicit. The strain-rate dependent model was adopted for hail while the Johnson-Cook damage constitutive model was adopted for the aluminum alloy layer. The 3D Hashin criterion damage model based on fracture energy was applied for the CFRP layer via the VUMAT subroutine. The cohesive element was inserted between the laminates to investigate the interlaminar damage. The accuracy of FEM was verified by comparing with the results obtained by tests. Combined with the energy absorption and internal damage mechanism, the effects of different parameters on the hail impact resistance of CARALL were studied.

Indentation modelling of aluminium cladding panels subjected to hailstone impact

In spite of colossal damage caused to aluminium panels in hailstorms, there is currently no rational design procedure found on research to regulate the design of building claddings or rooftops to withstand hail impact. Damage predictive models that have been reported in the literature are not suited to predicting hail induced damage. Thus, insurance premiums on damage to aluminium cladding caused by hail cannot be set to fairly distribute risks. In the current study, an analytical model for predicting permanent indentation generated by the impact of a hailstone is presented. The model was developed from a combination of plate theories and results from thirty-seven full scale impact experiments conducted on 900 mm ×900 mm aluminium panels. The model presented in this article takes into account strain rate effects and has been demonstrated to give predictions that are within some 10% difference from experimental measurements.

Experimental investigation of hail impacts over a wide range of high velocities

In the presented work, high velocity hail impact tests have been conducted on an instrumented rigid target. The synthetic hails, consisting of ice spheres with a nominal diameter of 48 mm and a mass between 50 and 55 g conditioned to temperatures in the range of -3, -20 and -50 °C were accelerated using a gas gun. The range of impact velocities was 46–314 m/s leading to maximal impact energies between 2000 and 3000 J which had not been investigated so far in the literature. Peak force and time to reach the peak force where extracted from the experimental tests. The obtained results were compared with results from the literature using empirical equations established in another publication from the literature. The obtained results confirm the trend reported in the literature in terms of dimensionless peak force versus dimensionless impact velocity. However, the dimensionless time to reach the peak force during the impact could not be compared successfully with previous results. The role of the target characteristics is estimated to be the reason for this difference.

Hail impact responses and residual tensile properties of CFRP T-joints

Hail impact is a major challenge encountered by aircraft in flight, and thus is a key concern in the design of damage-tolerant composite T-joints in aviation. The study uses the Z-pinning technique (the pre-hole insertion technology) in combination with fillets of two radiuses to manufacture four types of Carbon Fiber Reinforced Polymers (CFRP) T-joints. The T-joints are then subjected to hail impact tests at two energy levels, as well as post-impact quasi-static tensile tests. The results show that increasing the size of the deltoid and Z-pin-induced reinforcement has a limited influence on the responses of the T-joints to hail impact, but a significant influence on their residual tensile strength after impact. These influences are not only dependent on the structural characteristics of the T-joints, but are also closely related to the degree of discrete damage within the T-joints caused by hail impact. Acoustic Emission (AE) technology is used to monitor the quantitative evolution of damage to the T-joints in a timely manner during the loading process, and helps characterize the characteristics of evolution of various types of damage over different periods. The research here can help design lightweight and damage-tolerant T-joints.

Tensegrity-inspired triboelectric nanogenerator for broadband and impact-resistive vibration sensing

Vibration in the environment usually shows uncertainty with random changes in frequency and sudden acceleration impact. However, it is a huge challenge for existing vibration energy harvesters and sensors to work in random and even extreme vibration environments due to their rigid multi-component architecture with mechanical mismatches. Here, we propose a general design of vibration transduction with broadband response and high mechanical robustness that mimics the biological musculoskeletal system. Such design is based on a tensegrity structure, consisting of a rigid frame and soft strings, combined with triboelectric nanogenerator (TENG). The Tensegrity-inspired triboelectric nanogenerator is of broadband (0–200 Hz) frequency response and exhibits excellent impact resistance under high g acceleration impacts (105 g level). The device can still work normally after undergoing some structural damage. It has been successfully applied to the aeolian vibration monitoring of transmission lines and shows more reliable performance than commercial sensors when suffering the hail impact. Such tensegrity structure design has great potential in high-performance vibration monitoring in the industrial environment.

Numerical simulation on fracture mechanisms of CFRP with barely visible impact damage by hail impact

Numerical simulation on fracture mechanisms of CFRP with barely visible impact damage by hail impact

Impact of simulated hail damage at different growth stages and canopy positions on rainfed and irrigated winter wheat

AbstractProducers and crop insurance providers will benefit from an accurate assessment of yield reduction after hailstorms that considers crop management, weather, growth stage, and impacted part of crop (hail affected canopy position). But, limited information is available. The main objectives of this study were to quantify wheat (Triticum aestivum L.) yield losses associated with simulated hail damage timing and canopy position. The study was conducted in two locations (Garden City [irrigated], and Manhattan [rainfed]) in Kansas, from 2018 to 2020 and 2016 to 2018, respectively. Treatments were an incomplete factorial combination of stem bending at seven flowering stages, above or below the flag leaf and a nontreated control. Results of the study indicated 11%–22% wheat yield reduction due to simulated hail damage above the flag leaf and 32%–52% due to hail impact below the flag leaf under irrigated conditions. Within the high‐yielding rainfed environment, hail damage caused up to 20% yield reduction compared with the control. In rainfed and low‐yielding environments, the impact of hail damage was mainly dependent on the growth stage of wheat at hail occurrence. Hail damage at Feekes 11.2–11.4 stages decreased yield by 20%–50% from the rainfed control. Hail damage at Feekes 10.0–10.5.4 decreased yield by 50%–70% from the rainfed control. We provide empirical evidence that indicates hail damage on wheat is dependent on the interaction effect of in‐season crop water management, weather, canopy position and crop growth stage, and estimates of yield loss due to hail should consider these factors.