Flexural Impact Tests Research Articles

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.

Degradation of Roller‐Compacted Concrete Subjected to Freeze‐Thaw Cycles and Immersion in Potassium Acetate Solution

Two sets of roller‐compacted concrete (RCC) samples cured for 28 days were subjected to freeze‐thaw (F‐T) cycles and immersion in laboratory conditions. F‐T cycles in water and water‐potassium acetate solution (50% by weight) were carried out and followed by the flexural impact test. The weight loss, the dynamic elastic modulus (Ed), the mechanical properties, and the residual strain of RCC were measured. The impact energy was calculated based on the final number of the impact test. The results show that the effect of F‐T cycles in KAc solution on the weight loss and Ed of RCC is slight. Ed, the compressive strength, and the flexural strength of RCC with 250 F‐T cycles in KAc solution decrease by 3.8%, 23%, and 36%, respectively. The content (by weight) of K+ at the same depth of RCC specimens increases with the increase of F‐T cycles. The impact energy of RCC specimens subjected to 250 F‐T cycles in KAc solution decreases by nearly 30%. Microcracks occur and increase with the increase of F‐T cycles in KAc solution. The compressive strength of RCC immersed in KAc solution decreases by 18.8% and 32.8% after 6 and 12 months. More attention should be paid to using KAc in practical engineering because both the freeze‐thaw cycles and the complete immersion in KAc solution damage the mechanical properties of RCC.

Effect of flexural impact on freeze–thaw and deicing salt resistance of steel fiber reinforced concrete

The flexural impact performance, freeze–thaw and deicing salt resistance of steel fiber reinforced concrete (SFRC) were investigated in this paper. Pre-applied flexural impact tests were carried out and followed by 100 and 200 freeze–thaw cycles in 3 % NaCl solution. The dynamic elastic modulus and the weight loss of SFRC were measured, respectively. The weight loss measured in this paper is connected to a combination of scaling and absorption. Finally, all specimens were subjected to flexural impact tests again until one part of the specimens contacted the lifting pallet. The final numbers of flexural impact tests were recorded. The results show that the pre-applied flexural impact tests substantially decrease the dynamic elastic modulus of SFRC and increase the weight loss of SFRC under the action of freeze–thaw cycles in 3 % NaCl solution. The pre-applied flexural impact tests have an effect on the final number of flexural impact test of SFRC with 100 freeze–thaw cycles in 3 % NaCl solution. However, for SFRC subjected to 200 freeze–thaw cycles, the final impact number decreases slightly and then slightly increases. The severe combination of flexural impact and freeze–thaw exposure indicates that the two forms of deterioration affect the accumulated damage in a complex way.

Low-velocity flexural impact response of steel fiber reinforced concrete subjected to freeze–thaw cycles in NaCl solution

The flexural impact responses of steel fiber reinforced concrete (SFRC) with freeze–thaw cycles in 3.0% NaCl solution were investigated in this paper. Freeze–thaw cycles were carried out and followed by the flexural impact test. The weight loss and the residual strain of SFRC were measured, respectively. The results show that 1.5% (by volume) steel fibers addition has a little effect on the weight loss of concrete subjected to the freeze–thaw cycles in 3.0% NaCl solution. Both the bottom and side residual strain increase with the increasing of flexural impact test. For SFRC subjected to 0, 100, 150, 200 freeze–thaw cycles, the relationships between the residual strain and the number of impact test can be fitted by exponential functions with a good correlation coefficient. The effect of freeze–thaw cycles in 3.0% NaCl solution on the initial impact strength is slight. However, the initial impact strength decreases obviously after SFRC specimens are subjected to 250 freeze–thaw cycles.

Characterisation of the impact behaviour of polymer thermoplastics

One of the most important features when predicting the impact response of plastic components is the characterisation of the material in impact conditions. In this work, a new method to obtain stress/strain curves of thermoplastics at constant strain-rates is proposed. Instrumented tensile-impact tests have been performed on polypropylene samples at different impact energies. The use of tensile-impact techniques avoids some problems associated with flexural impact tests, and permits to determine the stress/strain curves and the strain-rate dependence of thermoplastics' behaviour in impact conditions. The results show that in the range of strain-rates analysed, polypropylene has an elastic–plastic behaviour with a slight plastic strain hardening. The isostrain-rate stress/strain curves can be used as material data in finite element simulations of impact events.

Polycarbonate/ABS blends: Processability, thermal properties, and mechanical and impact behavior

AbstractPC/ABS blends, encompassing the whole composition range between PC and ABS, were prepared by a Brabender‐like apparatus and compression molded in sheets. The analysis of processability, confirming the improved PC processability by ABS additions, was accomplished by the same apparatus used for the blend preparation. A DSC investigation confirmed the inward Tg shift found by other authors. Two very different mechanical tests were performed: (a) tensile stress–strain on unnotched specimens at a very low deformation rate, showing a decreased PC ductility in blends with ABS additions; and (b) flexural impact tests (Charpy mode) on sharply notched specimens at a very high deformation rate, where a strong synergistic effect was detected in a restricted composition range (20–30% ABS). A comparison of the experimental data of the Young's modulus versus blend composition with the Kerner's model predictions confirmed the good adhesion existing between PC and ABS domains. The results were interpreted on the hypothesis of interlayer zones existing at the PC/ABS boundary. © 1994 John Wiley & Sons, Inc.

合成樹脂の破砕エネルギーに関する検討

The size reduction of waste polymers has become an important subject in the field of waste reclamation.Therefore the investigation carried out on the impact and compressive fracture energy of synthetic resins by using four kinds of unsaturated polyester resins whose rheological properties are different. The specific fracture surface energies were determined by means of flexural impact tests and compressive tests with different rates of loading.It was found that the values of specific fracture surface energy were greatly influenced by the nature of resins and their viscous flow priperties and that the fracture energy was dependent on the load velocity.

Force–displacement evaluation of macromolecular materials in flexural impact tests. II. Influence of rubber content, degree of grafting, and temperature on the impact behavior of ABS resins

AbstractThe impact behavior of ABS (acrylonitrile–butadiene–styrene) resins was studied by measuring the force–deflection curve generated during flexural impact tests. Each curve is characterized by a limited number of significant parameters. Their dependence on the following constitutive or ambient variables was investigated: content of butadiene rubber, degree of grafting of acrylonitrile and styrene onto polybutadiene, and temperature. The results are analyzed phenomenologically and are tentatively interpreted in the light of possible micromechanical mechanisms.