Evaluation and prediction of material fatigue characteristics under impact loads: review and prospects

PurposeThe properties of materials under impact load are introduced in terms of metal, nonmetallic materials and composite materials. And the application of impact load research in biological fields is also mentioned. The current hot research topics and achievements in this field are summarized. In addition, some problems in theoretical modeling and testing of the mechanical properties of materials are discussed.Design/methodology/approachThe situation of materials under impact load is of great significance to show the mechanical performance. The performance of various materials under impact load is different, and there are many research methods. It is affected by some kinds of factors, such as the temperature, the gap and the speed of load.FindingsThe research on mechanical properties of materials under impact load has the characteristics as fellow. It is difficult to build the theoretical model, verify by experiment and analyze the data accumulation.Originality/valueThis review provides a reference for further study of material properties.

Mechanical response of aluminum foam sandwich structure under impact load

This study investigates the mechanical response of aluminum foam sandwich panels, sandwich cylindrical shells, and sandwich shallow shells under impact loads. First, a finite element model of the sandwich panel was established, and an impact load was applied. The numerical results were compared with theoretical and experimental results to verify the model's effectiveness. Second, the energy absorption efficiency and overall deformation of sandwich panels, sandwich cylindrical shells, and sandwich shallow shells under the same impact load were studied. The research shows that the energy absorption performance of the sandwich shells is better than that of the sandwich panels, and the overall deformation is less than that of the sandwich panels. The effect of increasing panel thickness on the two types of sandwich shell studies is based on this basis. The conclusions describe that increasing the panel thickness will significantly reduce the structure's energy absorption efficiency and deformation. Finally, the effect of single-and double-layer structure on the impact resistance of sandwich shells was studied when the total thickness of the sandwich structure was unchanged. The results show that compared with the single-layer structure, the energy absorption efficiency, overall deformation, and contact force between the projectile and structure of the double-layer structure will be reduced.

Natural Fibers vs. Synthetic Fibers Reinforcement: Effect on Resistance of Mortars to Impact Loads

Given their specific properties, their natural and renewable sources and their low environmental impact in production, natural fibers offer an opportunity for the development of eco-friendly cement-based composites. The main objective of this experimental work is to evaluate the resistance to the impact load of mortars incorporating natural fibers or polypropylene fibers at 28 days. The assessment was carried out according to an experimental protocol developed in our laboratory. The method consists in dropping a metallic ball on a square shaped specimen of 30x30x2 cm3 to determine the energy supported by each sample. For each specimen, the number of blows required for the first crack initiation and for the total collapse of specimen are detected using a device allowing to measure the speed of ultrasonic waves. The device was fixed on the specimen itself. In order to fulfill the mechanical identity card of the composites, flexural and compression tests were also carried out at 28 days. In this experimental protocol, the pozzolanic binder was considered with different fiber percentages of polypropylene (0.25% and 0.5% by mass of binder) and of natural fibers (0.5% and 1% by mass of binder). All fibers have a length of 12 mm. Results show that natural fiber reinforcement could be considered as an ecological alternative to polypropylene fiber one to improve the resistance of mortars to impact loads.

Stability Evaluation Method of Hole Wall for Bored Pile under Blasting Impact

Blasting impact load may be encountered during the construction of some pile foundation projects. Due to the effect of blasting impact, hole collapse can easily occur in the hole-forming stage of pile foundation construction. In order to prevent hole collapse, it is very necessary to evaluate the stability of a pile hole wall before pile foundation construction. The calculation of hole collapse can usually be attributed to an axisymmetric circular hole stress concentration problem. However, the existing collapse failure theory of pile hole hardly considers the effect of blasting impact load. In view of this, this paper proposes the stability evaluation method of a pile hole wall under blasting impact. Compared with the existing collapse failure theory, the proposed method fully considers the effect of blasting impact stress. Using Mohr–Coulomb strength theory and symmetry analysis, the strength condition of collapse failure is established in this work for accurate evaluation of the stability of a hole wall. The proposed stability evaluation method is demonstrated by a pile foundation construction project of a bridge. Moreover, a shaking table test on the pile hole model was performed to verify the proposed method by experimental data. The results indicate the effectiveness and usability of the proposed method. The proposed method provides a feasible way for the stability analysis of a pile hole wall under blasting impact.

Dynamic Wheel-Rail Force-Based Track-Irregularity Evaluation for Ballasted Track on Serviced Railway by Adjacent Excavation

This study investigates a load-based, track-irregularity-analysis technique for ballasted tracks on a serviced railway line with respect to excavation work conducted in adjacent sites. A numerical analysis and field measurements (railbed-settlement-monitoring sensor, track-geometry-measurement system, wheel-load measurements) were analyzed comparatively to demonstrate the correlation between the track irregularities and the Wheel-Rail interaction force. In this way, we highlight the necessity for load-based track-irregularity-management methods. The analyzed results show that the maximum dynamic wheel load was measured in the range of approximately 10 m before and after the location where the maximum track irregularities occurred, and that even if the maintenance criteria of track irregularities were satisfied, the design dynamic wheel load could still be exceeded depending on the train speed, thus indicating that track damage can be caused by the impact load.