Papers by Keyword: Impact Loading

Abstract: Assessment of structural responses to dynamic loads, such as impact, is essential because these loads can cause severe damage to infrastructure and pose risks to human lives. Important elements of structures, like bridge piers and building columns, are particularly vulnerable to impact loads from vehicle collisions or rockfalls. To address such critical loading, we conducted impact tests to analyze the responses of post-tensioned steel-reinforced concrete (RC) column sections under controlled impact loads. A large drop tower was used to accelerate a rigid cylindrical projectile with a flat nose, having a diameter of 100 mm, a length of 380 mm and a weight of 21.6 kg. Reaction forces were measured using load cells, while accelerometers captured high dynamic accelerations during impact. Both the reinforced concrete columns and the impactor were equipped with a speckle pattern, facilitating Digital Image Correlation (DIC) analysis. The DIC system was used to track the impactor velocity, to measure deflections, and to observe of the cracking patterns on the column surfaces. In total, six 200 mm × 300 mm × 1500 mm different column specimens were tested under two distinct impact velocities: 25 m/s and 33 m/s. The clear span was 1000 mm and the longitudinal and transverse reinforcement ratios were approximately 2 % and 0.7 %, respectively. Four columns were post-tensioned to two levels of 34 % and 67 % of their axial capacity and compared to two reference specimens with no axial force. This range of axial force was chosen to have a detailed evaluation of how different levels of post-tensioning influenced structural performance, specifically in terms of reaction force, lateral deflection and cracking patterns under impact loading. We observed that the mass of debris generated by the impact increased with impact velocity. In most cases, the debris mass also increased with a higher axial force ratio. This trend is likely due to the release of elastic energy stored within the post-tensioned specimen during the impact event, which intensified the dynamic response. Specifically, we noted a pronounced spalling of the concrete cover, primarily on the rear side of the impact, which led to the exposure of the reinforcement. The results of this study can serve as basis for analytical and numerical models and as guideline for testing additional parameters in similar specimens.

Abstract: Metamaterials have emerged as promising candidates for protective structures due to their lightweight design and energy absorption capabilities. While various lattice-based architectures have been explored, further research is needed to optimize their dynamic response and computational modeling. Recent studies highlight the superior strength-to-weight ratios of lattice metamaterials over traditional foams, yet challenges remain in balancing predictive accuracy and computational efficiency.This study introduces novel computational frameworks for the design and analysis of deterministic, hybrid, and stochastic lattice architectures. Using finite element models, different unit cell configurations are evaluated under dynamic loading, comparing beam-based models for efficiency with 3D solid models for accuracy. A comparative assessment with foam materials further examines energy absorption performance.The framework developed in this study provides a versatile tool for the automatic generation and analysis of lattice structures. Moreover, this study provides critical insights into lattice topology, computational trade-offs, and impact resistance.

Abstract: Currently, significant part of advanced air transport structural elements is made of fiber-reinforced polymer composite materials (PCM), in particular, carbon plastics. In order to increase the resistance of these materials to static electricity and lightning discharges while air transport passes through lightning fronts, lightning protection coatings in the form of copper grids are incorporated into PCM structure . For load-bearing structures and aircraft shells, the influence of dynamic loads in the form of low-cycle high-amplitude loading and hitting by solid objects is typical. The presence of inbuilt metal structure introduces additional uncertainty into the anisotropic PCM perception of these loads. Studies of the strength of carbon-fiber-reinforced plastics with built-in LPC at low-cycle loading and their perception of shock load has been carried out. It is established that short-term processing in the microwave electromagnetic field leads to an increase in the strength of the samples under low-cycle loading by 210%. CFR with LPC absorbs a part of the shock impulse and does not transfer it completely to subsequent structures. The microwave electromagnetic field helps to improve the damping properties of materials by 19.5% in average with a low impact energy. With an increase in the impact force energy, the effect of the microwave electromagnetic field is manifested to a less extent; further improvement of the damping properties does not occur. It increases the elastic characteristics of the material and practically does not lead to cracking and exfoliation of the surface layer in the impact area. The results can be used in the development of technologies for final processing of the products made of PCM in order to increase their resistance to dynamic loads.

Abstract: Biodegradable composites are highly encouraged to replace the traditional composites to promote the frangibility and environmental sustainability. In this paper, impact response of natural fiber reinforced composites is carried out by using drop mass set-up. Sisal and coir fibers are reinforced in epoxy matrix and the laminates are made by compression moulding process. Experiments are conducted to predict energy absorption and peak contact force during impact of 6 kg mass. Results are analyzed to find suitability of natural fiber reinforced composites in order to derive the suitable materials for frangibility application.

Abstract: This paper discusses the energy absorption during low velocity impact on target with combinations of PU foam, SiC inserts/plate bonded to GFRP composite backing. SiC inserts and SiC plates are bonded as front layer to enhance energy absorption. Low velocity impact is conducted by using drop mass set-up and mild steel spherical nosed impactor is used for impact testing of target in fixed boundary conditions. Failure in the case of SiC inserts is local as only the insert under the impact is damaged and nearby areas are intact. However, in the other cases, the SiC plate is damaged along with fiber failure and delamination on the composite backing layer. It is observed that the energy absorbed by SiC plate is higher than that absorbed by SiC inserts layered target.

Abstract: In this paper, static and dynamic crack analysis in two-dimensional functionally graded piezoelectric composites is presented. For this purpose, a time-domain boundary element method is developed. The collocation method is used for the spatial discretization of the time-domain boundary integral equations, while the convolution quadrature is adopted for temporal discretization. Since fundamental solutions for functionally graded piezoelectric materials are not available, a boundary-domain integral formulation is derived. The Laplace transformed fundamental solutions for homogeneous piezoelectric materials are applied. Special regularization techniques based on a suitable change of variables are used to deal with the singular boundary integrals. The radial integration method is adopted to compute the resulting domain integrals. Adjacent the crack-tips are square-root elements implemented to capture the local square-root-behaviour of the generalized crack-opening-displacements properly. An explicit time-stepping scheme is obtained to compute the unknown boundary data. Numerical examples will be presented to show the influences of the material gradation, poling direction and the transient dynamic loadings on the intensity factors.

Abstract: A novel experimental method was proposed for characterizing the energy absorbing capability of composite materials during the progressive crushing process under impact loading. A split Hopkinson pressure bars system was employed to carry out the progressive crushing tests under impact loading. The stress wave control technique was used to avoid the inhomogeneity of dynamic stress field in the specimen. The progressive crushing behavior was successfully achieved by using a coupon specimen and anti-buckling fixtures. With increasing strain rate, the absorbed energy during the crushing process slightly decreased, whereas the volume of the damaged part clearly increased regardless of material type. Consequently, the energy absorbing capability decreased with increasing loading rate. The effects of material composition, such as fiber type, matrix type and fabric pattern, on energy absorbing capability were also investigated by using the proposed method.

Abstract: The effect of fibre type and fibre amount on physico-mechanical properties of slurry infiltrated fibre concrete (SIFCON) at both quasi-static and dynamic load was evaluated experimentally. SIFCON is a special type of cement-based composite with high fibre volume fraction, extremely strong and ductile. Test specimens were prepared with 7 types of steel fibres (with different shape and mechanical parameters) in four volume fractions (7.5-15 vol. %). High performance fibre-reinforced concrete (HPFRC) has also been cast and tested for comparison purposes. The impact test has been carried out by using an in-house manufactured impact testing machine based on drop test principle. The test results revealed that SIFCON slab with 15 vol. % fibre content exhibits superior energy-absorption characteristics when compared to other slab specimens. Diameter of the fibres plays an important role for both strength and energy absorption capacity of SIFCON - using of low-diameter fibres with higher aspect ratio leads to the best results.

Abstract: The main objective of this experimental study was to investigate the effects of low velocity impact loading on the pressure bearing capacity of the E-glass/epoxy composite pipes. The pipes were produced by the conventional filament winding technique comprises of six axisymmetric layers with (±55°)₃ winding angles. The specimens were impacted at three different energy levels which are 5 J, 7.5 J, and 10 J using an instrumented drop weight impact testing machine (IMATEK IM10). The samples were then filled with water and subjected to burst test until distinct leakage failure is observed. The results indicate that the peak force and contact time increases with increased of impact energy. For impacted samples, the pressure tests show that the burst strength of the pipes decreases with increase in energy levels during impact loading. During the burst tests, several damage types named leakage and eruption were observed.

Abstract: In order to study the influence of freezing and thawing on the dynamic behavior of ceramsite concrete, specimens with four kinds of ceramsite volume fraction including 0%, 15%, 30% and 45% which subjected to 0, 10, 20, 30 and 40 cycles of freezing and thawing respectively, are tested by means of the Spilt Hopkinson Pressure Bar technique. The experimental results showed that under dynamic loading the ceramisite concrete was weakened with increasing of the number of freeze-thaw cycles. Changes of dynamic compressive strength and damage evolution affected by freeze-thaw cycling and volume fraction of ceramsite are discussed in the paper.