Flexural Impact Research Articles

Repeated impact resistance of steel fibre-reinforced dry UHPC: Effects of fibre length, mixing method, fly ash content and crumb rubber

Dry concrete exhibits significantly different mechanical properties and failure patterns under dynamic loads from those under static conditions. Considering the practical applications of dry concrete, the flexural impact load renders its units/structures susceptible to unpredictable damage or even failure. In this study, the modified low-velocity drop-weight impact test was conducted on steel fibre-reinforced dry UHPC (FR-DUHPC) beam samples to simulate the frequent and multiple impact loads. The effects of steel fibre length, mixing method, fly ash content and crumb rubber addition on the impact resistance of FR-DUHPC were evaluated based on dynamic responses. Weibull distribution was then conducted to analyse the failure hit number of concrete samples in consideration of the large value variation. Test results indicated that the flexural impact performance was markedly improved with longer steel fibres, but deteriorated with increased fly ash content (especially at early ages) and considerably degraded with the inclusion of rubber aggregate. Hybrid medium/long fibre reinforcement was proposed for DUHPC that were mainly subjected to impact loads during service, while the fly ash content utilized to partially replace cement was not recommended to exceed 40%. Rubber aggregate was not proposed to be added to dry concrete mixtures since the impact load would greatly accentuate the initial matrix defects caused by the weak bonding. Additionally, the two-parameter Weibull distribution was verified to be a desirable statistical method for analysing the failure blow number of FR-DUHPC under repeated low-speed drop-weight impacts. The impact energy for the practical structural design could be preliminarily computed utilizing the derived Weibull parameters at different levels of reliability.

Elastoplastic Quasi-Static and Impact Load Response of Steel Structure Sub-Assemblage with CFRP Strips

Presented in this paper is the outcome of an experimental investigation of the elastoplastic quasi-static and impact load response of a steel sub-assemblage constructed using a pair of hollow square section members with or without Carbon Fiber Reinforced Polymer (CFRP) strips. The sub-assemblage consists of a long structural member welded to a short member, thus representing a typical combination of a column and a beam on the face of a multi-story steel building frame. The column is subjected to a lateral quasi-static or impact load. Tests are conducted on four separate steel sub-assemblages. The first two tests are conducted with a gradually increasing flexural load applied at the midspan of the column up to the collapse condition without and with CFRP strips, respectively. Additional two tests are performed with a flexural impact load applied at midspan of the column also both without and with CFRP strips, respectively. The results of the study show that CFRP strips substantially increase the quasi-static collapse load of the sub-assemblage. However, when subjected to an impact load, the steel structure sub-assemblage with CFRP strips developed smaller strains in comparison with those without the CFRP strips. The post-impact time-dependent strains also became considerably smaller for the sub-assemblage with CFRP strips.

Research on the Bending Impact Resistance and Transverse Fracture Characteristics of Bamboo under the Action of Falling Weight

Drop weight impact tester was used to accurately measure the bending impact resistance of various parts of Phyllostachys edulis, commonly known as moso bamboo, with a growth cycle of 3–8 years. Cellulose crystallinity in the bottom (B), middle (M) and top (T) of bamboo at different ages was calculated using peak height analysis in X-ray diffraction. Heatmap of Spearman correlation analysis was used to represent the correlation between chemical composition and impact mechanics. The breaking load (BL), fracture energy (FE) and impact deflection (ID) of 3–8-yearold bamboo were found to be in the range of ~670–2120 N, ~5.17–15.55 J, and ~3.60–~17.76 mm, respectively. As the growth period of bamboo rises, the cellulose crystallinity at the B and T decreases first and then increases, while that for the M increases first and then remains stable. Similarly, the bending impact performance of bamboo was found to become stable with its growth and age. The flexural impact and toughness of the 4-year-old bamboo base material were better than other specimens. The enhancement in the bending impact properties of bamboo at different growth periods was influenced by the lignin content, while the value of FE was mainly positively correlated with ash, cold and hot water extracts and benzyl alcohol content. However the content of holocellulose and pentosan, air-dry density and, base density negatively influenced the FE. With the change in the height of the bamboo, the correlation between its impact mechanical properties and chemical composition gradually decreased. This study provides data support and theoretical basis for the age-appropriate thinning and application of moso bamboo.

Factorial Experimental Design to Study the Effects of Layers and Fiber Content on Concrete Flexural Behavior

Experimentation has come a long in helping researchers achieve breakthroughs in their different scientific areas and engineering happens to be one of those areas with the most impact from experimental advancement. The need for valid experimental results free from biases and confounding conclusions has prompted the development of new experimental techniques that takes consideration of all applicable factor and combinations in providing answers on a research topic, and the Factorial Experimental design credited to Sir Ronald Fisher is one technique yielding highly valid results. This paper uses the factorial design of experiments to research the flexural impact of polyvinyl acetate fiber and layered concrete in construction. The experiment considered two levels of fiber contents and two levels of layers, and prepared samples with all combinations of the variable factors. The samples were tested after 7 days from casting for flexural strength and an advance statistical analysis was performed on the flexural responses of the samples using R-program. The results from the analyses revealed the significance of the variables to the flexural strength of the samples, as well as their interactions. The experiment concluded that based on the number of layers and fiber content used for the experiment, casting concrete in layers does have a significant negative effect on the flexural strength of concrete, and the failure pattern of concrete members under flexural load in evidently influenced by the material composition of the concrete, and that it can be evidently influenced by casting the concrete in layers.

Flexural response of TRM subjected to low-velocity impact loads: Experimental and analytical study

A constitutive approach to investigate the flexural impact performance of textile-reinforced mortar (TRM) is presented in this study. Experiments were performed under three-point bending conditions on a drop-weight impact system at 1, 2, 3, 4, and 4.5 m/s. Experimental results showed that the differences in peak load from 4.5 to 1 m/s were 1.964 kN (for BTRM-4) and 2.191 kN (for BTRM-6), and in energy absorption from 4.5 m/s to 1 m/s incident velocities were 2.66 J (for BTRM-4) and 2.98 J (for BTRM-6). Additionally, analytical modeling of experimental results was performed to identify the correlation between the experimental and analytical results. The parameters for a strain-hardening material model were obtained by using closed-form equations. The prepared model could reproduce a tripartite load-displacement response related to pre-cracking and post-cracking behavior. The results also verified that the best agreement between the analytical model and experimental data was achieved by considering scattering, softening, and reinforcement waviness in cement matrix under different loadings. The tensile properties of the tested samples were predicted by using an inverse algorithm and model parameters. Notably, the parametric model overpredicted the simulated three stages of TRM composites. Results could be used as average load values in the structural design and analysis of cement-based material composites under different impact loads.

Flexural Impact Performance of Stainless Steel–Lightweight Concrete Composites for Marine Structures

Flexural Impact Performance of Stainless Steel–Lightweight Concrete Composites for Marine Structures

Effect of Initiator and Accelerator Amounts on Mechanical Properties of Unsaturated Polyester Resin

This research focused on the effect of initiator and accelerator amounts on mechanical properties of unsaturated polyester resin (UPR). Methyl ethyl ketone peroxide (MEKP) and cobalt octoate (CoO) were used as an initiator and an accelerator, respectively. The amount of each chemical was varied from 1, 1.5 to 2 phr. In each batch, UPR, MEKP and CoO were mixed, casted and allowed for curing at room temperature for 24 hours. Mechanical properties of the cured samples were then studied. The results indicated that the effects of MEKP and CoO amounts on flexural properties and impact resistance were greater than those on hardness. It was found that UPR samples prepared by using the same ratio of MEKP and CoO exhibited overall mechanical properties better that those prepared with different MEKP and CoO ratios. When all mechanical properties were considered, the results suggested that the best overall mechanical properties were achieved when MEKP 1.5 phr and CoO 1.5 phr were employed.

Experimental and Analytical Modeling of Flexural Impact Strength of Preplaced Aggregate Fibrous Concrete Beams.

Preplaced aggregate fibrous concrete (PAFC) is a revolutionary kind of concrete composite that is gaining popularity and attracting the interest of academics from across the world. PAFC is a uniquely designed concrete prepared by stacking and packing premixed fibers and coarse aggregate in a steel mold. The gaps between the fibers and aggregates are subsequently filled by injecting a cement grout with high flowability. This study investigates the impact performance of three different sizes of PAFC beams. Steel and polypropylene fibers were used in a 3% dosage to make three different beam sizes, measuring 550 × 150 × 150 mm, 400 × 100 × 100 mm, and 250 × 50 × 50 mm. According to ACI Committee 544, all beams were subjected to a drop weight flexural impact test. Compressive strength, impact energies at initial crack and failure, ductility index, and failure mode were evaluated. Additionally, analytical modeling was used to compute the failure impact energy for the fibrous beams. The results showed that the addition of fibers increased the capacity of the tested beams to absorb greater flexural impact energy. Compared to polypropylene fibers, steel fibers had better crack propagation and opening resistance because of their higher tensile strength and crimped and hooked end configuration. For all large-size beams, the analysis of the percentage increase in impact energy at the failure stages was found to be 5.3 to 14.6 times higher than the impact energy at cracking.

Investigation of the effect of graphene nanosheets on the properties of beech/polylactic acid flour composites

In this study, the effect of different amounts of graphene on the physical and mechanical properties of polylactic acid beech wood fiber composites were investigated. Beech flour and graphene were used as reinforcing phases with different weight percentages (0, 0.5, 1.5 and 2.5%). Samples were prepared by solution method and after pressing, mechanical properties such as flexural strength, flexural modulus, impact resistance and tensile strength and physical properties including differential scanning calorimetry test (DSC) and X-ray scattering test were measured. The results of analysis of variance showed that the effect of treatment was significant for flexural strength ( p < .05) and flexural modulus, impact resistance and tensile strength ( p < .01). The highest flexural strength, flexural modulus and tensile strength were related to treatment 8, which included 30% beech flour, 67.5% polylactic acid and 2.5% graphene, and the highest impact resistance was related to treatment 2, which included 20%. The weight of beech flour was 79.5% by weight of polylactic acid and 0.5% by weight of graphene, which were significantly different from other treatments ( p < .05). Based on the DSC, the melting temperature of the polymer matrix was transferred to higher temperatures by adding graphene nanosheets. The results of X-ray diffraction test showed that for all three treatments there is a similar trend in terms of peak graph and with increasing the concentration of graphene nanoparticles, only the peak intensity changed. It can be said that the addition of nanographene to beech-polylactic acid flour composites has improved the mechanical and physical properties.

The Effect of Different Fibre Lengths on the Mechanical Properties of Biocomposites

Kenaf is a nonwoody fibrous plant, and its fibre can be potentially used as a reinforcement in the matrix to produce biocomposite materials. The properties of biocomposite materials are highly dependent on the reinforcing material and the matrix used as a binder. This study used kenaf fibre as a reinforcing material with different compositions (10, 20, and 30 wt.%) and different fibre lengths (1 cm and 3 cm) in the matrix using the casting process. Low viscosity epoxy resin (635 thin epoxy resin) with a viscosity of 6 poise was used as the matrix. The results showed that the highest flexural strength, impact strength and shore hardness were obtained at a 30 wt.% kenaf fibre composition with a 1-cm kenaf fibre length, namely, 85 MPa, 338 KJ/m2 and 98 SHD, respectively. The length of the fibre in the matrix affects the mechanical properties of the resulting biocomposite. This condition is caused by kenaf fibres with a length of 1 cm being more dispersed in the matrix than fibres with a length of 3 cm.

Influence of surface functionalization of ceramic nanofibers on morphological, physical and mechanical properties of unsaturated polyester nanocomposites

Alumina nanofibers at 0.25wt%, 0.5wt%, 0.75wt%, and 1wt% concentration were used to modify unsaturated polyester resin. Additionally, vinyl silane treated alumina nanofibers were used at the same concentrations and were compared to pristine alumina nanofibers. The SEM images showed a variation in the surface morphology when alumina nanofibers and the BET measurement showed surface area increase from 111 m2/g to 122 m2/g when nanofibers were treated with silane agent. The dispersion of alumina nanofibers into the host unsaturated polyester resin was successfully achieved by three roll mill dispersion. The TEM images showed good dispersion of alumina nanofibers in polyester resin. Although pristine nanofibers showed greater agglomeration at 1wt% concentration, the effect of agglomeration was reduced in the 1wt% concentration. The weight loss measurements from TGA showed that the thermal stability of nanocomposites increased with addition of nanofibers and the lower onset degradation temperature can be tailored to improve by a maximum of 5.5% for silane treated nanofiber. Viscosity and contact angle which are key factors affecting the processability has seen to be positively altered by silane treatment. Additional tensile, flexural, and Izod impact properties were evaluated for the nine material systems and the properties were summarized.

Polypropylene Composites Reinforced by Nonmetallic from Waste Printed Circuit Boards Using Spout-Fluid Bed Coating with PP Particles Enhance Fluidization

Nonmetallic materials recycled from waste printed circuit boards (N-WPCBs) were modified by coating KH-550 in a spout-fluid bed. To improve the effect of the modification, PP particles were used to enhance the fluidization quality of the N-WPCB particles in the coating modification. Then, the modified N-WPCBs were used as fillers to fabricate PP/N-WPCB composites. The method of coating in a spout-fluid bed with PP particles enhanced fluidization and showed the best modification effect compared to other coating methods. The FT-IR and SEM results demonstrated that interfacial bonding between N-WPCBs and PP could be enhanced by modified N-WPCBs, which improved the mechanical properties of the composites. When the mass ratio of PP to N-WPCBs is 100:75 and the dose of KH-550 is 4 phr, the flexural strength, tensile strength, and impact strength of the composites increase by 16.60%, 23.22%, and 23.64%, respectively. This would realize the high-value utilization of N-WPCBs with coating modification in the spout-fluid bed.

Impact Strength of Ferrocement Panel under Low Velocity Impact Loading

The capability to absorb energy, often called as toughness, is of importance in actual service conditions of mesh reinforced composites, when they may be subjected to static, dynamic and fatigue loads. Toughness evaluated under impact loads is the impact strength. The toughness of materials are determined by two methods, (i) by measuring deformation under impact load, (ii) by determining energy adsorption capacity of materials under impact load. Several methods were used to investigate to determining toughness of materials. In this research work, drop weight impact test were used. The present experimental work describes testing of flat ferrocement panels with different number of layer steel mesh as well as enhancement of panels with steel fiber. The main purpose of this study is to investigate the effect of using different number of wire mesh layer on the flexural strength and impact strength and also effect of varying thickness of panels on the energy absorption of ferrocement panels. The experimental work includes preparation of ferrocement panels reinforced with welded square mesh, woven square mesh with and without hooked steel fibers The ferrocement panels of different sizes were prepared and tested for flexural strength under the two point loading as well as drop weight for impact testing. It is expected that as the mesh layers will be increased the energy absorption capacity of the panel should be increased and the also its effect should be seen for addition of hooked steel fibers.

Flexural impact Response of Cracked Sandwich Beams Repaired by Composite Patches

Bu çalışma, deneysel ve sayısal olarak kompozit yamalar ile tamir edilen çatlaklı sandviç kirişlerin eğilme darbe davranışını araştırmaktadır. Sandviç kiriş elemanları yüzey tabakaları, cam elyaf takviyeli kompozit, köpük çekirdek, PVC malzeme ve yapıştırıcı tabakalardır. Üst yüzey tabakasına çatlak oluşturularak hasar verilmiştir ve kompozit yama yapıştırılarak tamir edilmiştir. Düşük hızlı darbe davranışı, farklı yama malzemeleri, kalınlıkları ve darbe enerjileri açısından incelenmiştir. Sayısal darbe analizleri, kompozit sandviç kirişin hasar davranışını modellemek ve deneysel darbe testi sonuçlarını karşılaştırmak için yapılmıştır. PYTHON program dili ile parametrik modelleneme yapılmıştır. Sonlu elemanlar alt programı ABAQUS-VUMAT kullanılarak 3B Hashin hasar modelleri kompozit yama ve yüzey tabakalarına uygulanmıştır. Son olarak, hasarlı kirişin eğilme rijitliği yama uygulaması ile artırılmıştır. Sandviç kirişlerin hasar toleransları, temas kuvveti değişimleri, kinetik enerji varyasyonları ve darbe sonrası hasar modları dikkate alınarak farklı yama parametreleri için belirlenmiştir.

PLA-Cu reinforced composite filament: preparation and flexural property printed at different machining conditions

Fused Deposition Modeling (FDM) is commonly used to construct complicated design, especially for medical applications. In the present work, 12 rate weight percentage of copper powder with a molecule size of 30–50 µm is used in the Poly Lactic Acid (PLA) matrix as a fortification to form a composite fiber. For the variable working conditions, the samples are printed to ASTM D-790. In FDM, layer height, bed temperature, and nozzle temperature are taken as variable parameters to measure the bending property. The Scanning Electron Microscope (SEM) and 3-dimensional optical pictures examine the flexural quality, crack mechanics, and impact of various printed conditions for three-point flexural tests. A layer thickness of 0.14 mm was recorded for the maximum flexural quality of 68.6 MPa. The fracture mechanism is considered as identical under any machining conditions. Layer height predominantly determines the material’s flexural property and the uniform dispersion of the copper molecule over the crack surface which is confirmed by surface topography. Also, the non-parametric Bayesian Additive Regression Trees (BART) model is created to benefit from the earlier use of this inferential structure to measure vulnerability and information alignment.

Flexural impact resistance of steel beams with rectangular web openings

This paper focuses on the flexural impact behaviour of steel I-beams with rectangular web openings. Published studies on impact resistance and design requirements of perforated steel beams are limited. To shed light such a topic, detailed non-linear three-dimensional finite element models (FEMs) were developed using ABAQUS. Rigorous validation process was employed to verify the FEMs built against published experimental tests in terms of force and displacement time histories. Reasonably good agreement was obtained between the numerical results and the corresponding experimental ones. Then, the validated FEMs were exploited to investigate the flexural impact resistance of perforated steel beams with rectangular openings. The factors examined in the current study were the area, depth, number and reinforcement of web openings under different impact velocities ranged between 2.214–7 m/s to provide comprehensive understanding on the flexural impact response of steel beams perforated with rectangular openings. It was observed that increasing the number of narrow web openings negligibly effected the flexural impact resistance of steel beams. Moreover, using wide openings significantly reduced the dynamic flexural resistance of such beams. Besides, slight effect on the flexural impact resistance and mid-span deflections were obtained if the depth of openings increased. Moreover, a considerable improvement was observed by providing perforated beams by horizontal steel reinforcement particularly for those with wide openings. The perforated steel beams showed similar mode of failure by generating four plastic hinges around the edges of an opening, which is the failure mode produced for perforated beams under quasi-static loading.

Tribological properties of bismaleimide alloy blend with a novel silicon dioxide-containing benzoxazine-monomer

ABSTRACT To overcome the limited tribological properties of bismaleimide (BMI) resin, a kind of novel organic–inorganic hybrid silicon dioxide nanoparticles with terminal functional amidogen groups (SiO2–NH2) was prepared via a sol–gel process. The SiO2–NH2 was chosen as raw materials to react with polyformaldehyde and aniline, and the silicon dioxide-containing benzoxazine-monomer (SiO2-BOZ) can be obtained via a solvent process. The new prepared SiO2-BOZ were then as modified phase to modify BMI to prepare the SiO2-BOZ/BMI composites. With 15.0 wt-% SiO2-BOZ, the flexural strength and impact strength of SiO2-BOZ/BMI composites can reached the maximum value of 166.12 MPa and 17.93 kJ m−2, respectively, while the wear rate of SiO2-BOZ/BMI composites is only 3.9 × 10−6 mm3 N−1 m−1. The enhanced tribological properties of SiO2-BOZ/BMI can be attributed to the improvement of its heat resistance and mechanical properties, which can increase the capacity of the SiO2-BOZ/BMI to withstand external forces and heat during the friction process.

Impact Performance of Steel Fiber-Reinforced Self-Compacting Concrete against Repeated Drop Weight Impact

The self-compacting concrete (SCC) was invented to overcome the compaction problems in deep sections, owing to its perfect workability characteristics. Steel fibers when used with SCC would affect the required fluidity characteristics but improve its impact resistance. In this research, an experimental work was conducted to evaluate the impact response of micro-steel fiber-reinforced SCC, under flexural impact. A 5.47 kg free-falling mass was dropped repeatedly from 100 mm height on the top center of 270 mm-length beam specimens. Eight mixtures with two design grades of 30 and 50 MPa were prepared to distinguish the normal and high-strength SCCs. The distinguishing variable for each design grade was the fiber content, where four volumetric contents of 0%, 0.5%, 0.75%, and 1.0% were used. The test results showed that the impact resistance and ductility were significantly improved due to the incorporation of micro-steel fibers. The percentage improvements were noticeably higher at failure stage than at cracking stage. For the 30 MPa mixtures, the maximum percentage improvements at cracking and failure stages were 543% and 836%, respectively. Weibull’s linear correlations with R2 values of 0.84 to 0.97 were obtained at the failure stage, which meant that the impact failure number followed the Wiebull distribution.

Low velocity flexural impact behaviors of bamboo fiber reinforced composite beams

To investigate the anti-impact behavior and loading rate sensitivity of bamboo fiber reinforced composite (BFRC) beams, low-velocity-impact flexural experiments were performed under impact velocity changing from 2 m/s to 10 m/s. Quasi-static flexural tests were carried out under the same conditions to supply a quasi-static reference to the dynamic performance. Velocity-dependent effects of the impact force, the velocity, the impulse, the displacement and the absorbed energy were revealed by the weight-dropping experiments. The impact force, the energy absorption and the impact toughness increase nearly linearly to the impact velocity. These rate sensitivities of the BFRC beam were expressed quantitively by linear fitting equations, providing a basis to design shock and explosion resistant BFRC structures.

Crashworthiness enhancement of thin-walled hexagonal tubes under flexural loads by using different stiffener geometries

Thin-walled structure tubes have been widely used in automotive applications as energy absorber members due to the excellent energy absorption ratio to the weights. The purpose of this study is to enhance the energy absorption of the thin-walled hexagonal tube by using different stiffeners geometries under the flexural impact. The structure has been subjected to an impact velocity of 50 km/h with a striker mass of 1500 kg at a 90-degree angle as recommended by the technical protocol section of the Insurance Institute for Highway Safety (IIHS) side-impact crash test. Besides the empty tube and the foam-filled tube, nineteen stiffeners were used in this study. A comparison between the reinforced and non-reinforced structure was made in terms of the specific energy absorption (SEA) and the crushing force efficiency (CFE). The numerical results have shown that stiffeners have improved the crashworthiness parameters when compared with the conventional empty tube. The numerical results have revealed that the introducing stiffeners to the structure have enhanced the structure performance since the stiffeners restrict the flattening of the upper side when subjected to compressive loadings and the SEA was improved for different wall thickness used. The results have shown that the H-5 stiffener was chosen as the best geometry since the SEA was increased up to 114%, the CFE was enhanced by 27% and the bending resistance was also improved.