Repeated Impact Loading Research Articles

Structural toughness and interfacial effects of multilayer TiN erosion-resistant coatings based on high strain rate repeated impact loads

The mechanical performance of the coating is closely related to the surface loading characteristics. The performances of the aero-engine anti-erosion coating under high strain rate repeated impact load of sand are different from low speed and single impact load. However, the related impact response and mechanism have rarely been studied. We measured dynamic response characteristics of the coating subjected to high strain-rate repeated load using a nano-impact test device. Combined with the simulation calculation of the stress distribution, the strengthening-toughening mechanism of soft-hard alternating multilayer coating and the effect of the interface in impact damage were discussed. The results show that the soft-hard alternating multilayer TiN/Ti coating has a higher resistance to high strain-rate repetitive impact than the traditional monolayer TiN coating. Dislocations are difficult to pass through the TiN/Ti multilayer coatings interface under the interfacial effect, resulting in only slight plastic deformation. Furthermore, interfacial crack propagation was observed in TiN/Ti multilayer coatings. However, radial and severe brittle peeling off was observed in TiN monolayer coating. The introduction of the Ti layer promoted the formation of the shear band and increased the toughness, consuming impact energy and reducing the maximum compressive stress and shear forces. Moreover, it reduced the possibility of severe brittle fracture of the TiN/Ti multilayer coatings.

Laser Spot Welding and Electric Contact Points Using Copper/Single-Walled Carbon Nanotube Nanocomposite Synthesized by Laser Surface Implanting

In our previous studies, we have developed a wet process, denoted as laser surface implanting (LSI), to synthesize a copper/single-walled carbon nanotube (Cu–SWCNT) metal nanocomposite. The nanostructure of this Cu–SWCNT composite was shown to contain discernable SWCNT clusters in nanosizes inside the copper matrix. Its hardness could achieve up to three times that of pure copper, verified by micro-hardness and nano-hardness tests. A focus ion beam bombardment test and a plane strain compression test show 2.5 times toughness improvement for the Cu-SWCNT composite. Based on these strength improvements, two potential applications for the Cu-SWCNT nanocomposite are proposed and their feasibilities are verified using specially design test rigs. The first application is related to creating long lasting electric contacts. The result shows that the Cu-SWCNT nanocomposite is highly wear-resistant. The contact area of the simulated electric contacts increases after repeated impact loading, which potentially could lower the contact resistance. The second application is to use the Cu-SWCNT implants as high strength spot weld for joining copper foils. A smaller weld with a higher strength reduces the power requirement of the laser and, consequently, the thermal distortion for higher-dimensional precision. The specially designed test rig for the weld strength characterization is a new contribution, providing a new testing capability for small and non-homogeneous samples not suitable for a standard tensile test machine.

Critical distance model for the fatigue life analysis under low-velocity impacts of notched specimens

A fatigue life estimation method is proposed for the notched specimens under low-velocity repeated impact loadings. The stress concentration effect at the notch root is taken into account by the implementation of the Theory of Critical Distance, and the continuous variation of strain ranges at the critical point due to the plastic strain accumulation is considered by the mean strain modification. The impact fatigue experiment is conducted on the notched plate specimen of material S45C with the pendulum-type test machine, and the comparison with the numerical analysis results indicates that the proposed model gives a satisfactory prediction on the impact fatigue lives.

Improving the Fatigue of Newly Designed Mechanical System Subjected to Repeated Impact Loading

This paper develops parametric accelerated life testing (ALT) as a systematic reliability method to produce the reliability quantitative (RQ) specifications—mission cycle—for recognizing missing design defects in mechanical products as applying the accelerated load, expressed as the inverse of stress ratio, R. Parametric ALT is a way to enhance the prediction of fatigue failure for mechanical systems subjected to repeated impact loading. It incorporates: (1) A parametric ALT plan formed on the system BX lifetime, (2) a fatigue failure and design, (3) customized ALTs with design alternatives, and (4) an assessment of whether the last design(s) of the system fulfills the objective BX lifetime. A BX life concept with a generalized life-stress model and a sample size equation are suggested. A domestic refrigerator hinge kit system (HKS), which was a newly designed mechanical product, was used to illustrate the methodology. The HKS was subjected to repeated impact loading resulting in failure of the HKS in the field. To conduct ALTs, a force and momentum balance was utilized on the HKS. A straightforward impact loading of the HKS in closing the refrigerator door was examined. At the first ALT, the housing of the HKS failed. As an action plan, the hinge kit housing was modified by attaching inside supporting ribs to the HKS to provide sufficient mechanical strength against its loading. At the second ALT, the torsional shaft in the HKS made with austenitic ductile iron (18 wt% Ni) failed. The cracked torsional shaft for the 2nd ALTs came from its insufficient rounding, which failed due to repeated stress. As an action plan, to have sufficient material strength for the repetitive impact loads, the torsional shaft was reshaped to give it more rounding from R0.5 mm to R2.0 mm. After these modifications, there were no problems at the third ALT. The lifetime of the HKS in the domestic refrigerator was assured to be B1 life 10 years.

Bearing Damage Detection of a Bridge under the Uncertain Conditions Based on the Bayesian Framework and Matrix Perturbation Method

The bearing of a bridge, as a critical component, is important in the force transformation of the superstructure; however, due to the service condition and repeated impact load, the bearing is prone to be damaged but difficult to detect the damage; the present research has few studies that focused on the damage detection of the structural bearing. Meanwhile, practical engineering is always surrounded by variational environmental conditions, and sometimes, the element and bearing damage both exist in the structure. Thus, these uncertain conditions all cause inaccurate damage identification results using the vibration‐based damage detection method. In order to detect the damage of the structural bearing and improve the precision, firstly, the structural dynamic characteristic equation considering uncertain conditions has been deduced; then, a damage detection framework constructed by the Bayesian theory and perturbation method has been developed in this article; a numerical example of an 8‐span concrete continuous beam and a practical example of I‐40 steel‐concrete composite bridge are utilized to validate the feasibility of the proposed method, and single type and two types of damage cases are studied. The outcomes demonstrate that the damage of structural elements and bearings can be detected with high accuracy. The proposed method is of great applicability and good potential.

Strength, Load-deflection Behavior And Impact Resistance of Two-way Slab for Concrete Incorporating Waste Aluminum Fibers

This research investigated about the effectiveness of waste aluminum results from waste cans of gassy drink, as fibers in concrete. strengths, load-deflection behavior under flexural load and impact resistance under low velocity repeated impact load were investigated. Two length of fibers were examined 40 mm and 20 mm for 0%, 0.5%, 0.75% and 1% fibers content. Results showed that compressive strength has inconsiderable affected by adding fibers while splitting tensile strength, modulus of rupture and impact resistance for concrete incorporating aluminum fibers especially for 0.75% and 4-mm fibers have clear improvement. Compared to experimental results, ACI equation underestimated the tensile strength of fiber concrete. Load –deflection of beam with fibers showed a more ductile behavior at failure under flexural load compared to reference one. Bond strength improved by adding aluminum fibers. Slabs that incorporating aluminum fibers showed a higher energy absorbed, less deflection and smaller cracks width at failure than the one without fibers under impact loads. From results, one can see that mixes with 0.75% fibers showed a best performance compared with other mixes. Finally, the 40 mm fiber was more effective in improvement in concrete resistance than 20 mm fiber length.

Evaluation of the particle breakage of calcareous sand based on the detailed probability of grain survival: An application of repeated low-energy impacts

The detailed probability of grain breakage influences the micromechanical behaviours of granular soil under repeated impact loads. This study investigated grain breakage in single-sized and multi-sized calcareous sands under repeated low-energy impact loads. By introducing the dye tracing and particle image segmentation methods in impact tests, various-sized fragments and residual grains were distinguished and further quantitatively analysed. The experimental results showed that the probability of grain survival decreased with the increase in the repeated cycles of impact (total input work); large grains played a more important role in the latter breakage stage as the repeated cycles of impact increased. Compared with the commonly used index Bg, the breakage index Bs based on the detailed probability of grain survival was much closer to the actual amount of grain breakage for single-sized samples and was slightly larger than Bg for multi-sized samples. The detailed probability of grain survival and the indexes could be used for investigating mechanisms of grain breakage under repeated impact loading.

Time-varying structural reliability assessment method: Application to fiber reinforced composites under repeated impact loading

Reliability evaluations play a significant role in engineering applications to ensure the serviceability and safety of advanced structures such as those made of composites. Here, a dynamic reliability evaluation analysis based on the probability density evolution Method (PDEM) has been adapted to assess the reliability of composite structures under uncertainties within the material properties and the external loadings. A Back-Propagation Neural Network approach is employed to identify the system's nonlinear structural response, which is often the case under large deformations. To exemplify, a split Hopkinson pressure bar system was employed to mimic the mechanical behavior of a polypropylene/fiberglass woven composite plate structure under repeated high-strain rate impacts. Subsequently, the reliability prediction was performed offline via the system model and integration of uncertainties, as well as via an online SHM-based approach, and compared to full-scale (direct) experimental reliability values by repeating the impact tests on a population of samples. A material degradation factor has been introduced within the PDEM approach to account for surface damage induced during impacts. Results clearly showed the accuracy of the PDEM in predicting the remaining reliability of the composite after each impact. The method is generic and may be applied to other types of loadings and structures.

Dynamic mechanical behaviour and energy absorption of aluminium honeycomb sandwich panels under repeated impact loads

Sandwich structures are widely applied in the field of marine structure lightweight design and impact protection due to their excellent mechanical properties. In this paper, the dynamic mechanical behaviour and energy absorption characteristics of aluminium honeycomb sandwich panels (AHSPs) under repeated impact loadings are investigated. A three-dimensional elastoplastic finite element model of AHSP under repeated impact loadings is established by using the commercial software ABAQUS Explicit. The accumulation processes of plastic deformation, the impact force-displacement curves as well as the energy absorption performances are numerically calculated. Besides, the repeated impact experiments of AHSPs were conducted by using the drop-weight impact testing machine INSTRON CEAST 9350. Furthermore, the influences of geometrical parameters on the dynamic behaviours of AHSPs under repeated impact loadings are further performed. Results show that the numerical calculated results are in good agreement with the experimental results. With the increase of the repeated impact numbers, the bending deflections of both top and bottom face sheets of AHPSs accumulate gradually, the compressive deformations of the honeycomb cores enlarge gradually and finally the densification phenomenon appears. The deformation mode of bottom face sheet experiences the mode transition from the global bending deformation model to the coupling deformation mode of the global bending deformations and the local indentations.

A Simplified Analytical Solution of Mechanical Responses of Soil Subjected to Repeated Impact Loading

A simplified dynamic response model is proposed based on the deformation and dynamic stress response characteristics of soil under impact loading. The foundation is divided into two distinct zones: a projection cylinder acting vertically under impact loading and a hollow cylinder outside the projection area. It is assumed that the ramming deformation of the projected cylinder under the vertical impact load is a quasi-static loading process under the maximum contact dynamic stress through the quasi-static method, and the settlement calculation without lateral deformation is given. It is assumed that the inner wall of the hollow cylinder is subjected to horizontal lateral pressure and the analytical solution of the horizontal dynamic stress considering the plastic deformation of soil is given. The simplified dynamic response model can reflect the mechanical response of soil under impulse train load well which can provide reference for similar projects.

Evalutions of strengths, impact and energy capacity of two-way concrete slabs incorprating waste plastic

This work is about investigated the effectiveness of inclusion of local waste, represented by plastic water drink bottles caps (CPPA), in the concrete as a partial substitute for coarse aggregates. Compressive, flexural and splitting strengths were evaluated for plain concrete. For reinforced concrete (R.C.), bond strength between reinforced bar and surrounding concrete has been evaluated. In additional, impact resistance, energy absorption capacity, mid-span deflection and crack width for Two-way R.C. slab subjected to repeated impact load have been evaluated. Five different content of plastic aggregate were examined; 0%, 15%, 30%, 45%, 60% and 75% of CPPA. Tests Results showed that strengths (compressive, splitting, flexural and bond strengths) improved for plastic content 15% and 30% especially at 15%. While these strengths began to decrease with increasing plastic's content over 30%. For R.C. slabs, number of blows that caused failure increased with increasing plastic content up to 45%, which mean increasing in impact resistance and increasing in energy-absorbed capacity. Based on the experimental results, empirical equations were proposed of calculating splitting, flexural, bond strengths and energy-absorbed capacity for concrete incorporating CPPA. According to results of this investigation, for structural reinforced concrete, 15% and 30% of this type of plastic is recommended to be used as partial replacement of gravel.

Impact Response of Hammerhead Pier Fibrous Concrete Beams Designed with Topology Optimization

Reducing the weight of concrete beams is a primary (beyond strength and durability) concern of engineers. Therefore, this research was directed to investigate the impact response of hammerhead pier concrete beams designed with density-based method topology optimization. The finite element topology optimization was conducted using Autodesk fusion 360 considering three different mesh sizes of 7 mm, 10 mm, and adaptive meshing. Three optimized hammerhead beam configurations; HB1, HB2, and HB3, respectively, with volume reductions greater than 50 %. In the experimental part of this research, nine beams were cast with identical size and configuration to the optimized beams. Three beams, identical to the optimized beams, were tested under static bending for verification purposes. In comparison, six more beams, as in the preceding three beams but without and with hooked end steel fibers, were tested under repeated impact load. The test results revealed that the highest flexural capacity and impact resistance at crack initiation and failure were recorded for the adaptive mesh beams (HB3 and HB3SF). The failure impact energy and ductility ratio of the beam HB3SF was higher than the beams HB1SF and HB2SF by more than 270 %. The results showed that the inclusion of steel fiber duplicated the optimized beam’s impact strength and ductility several times. The failure impact resistance of fibrous beams was higher than their corresponding plain beams by approximately 2300 to4460 %, while their impact ductility ratios were higher by 6.0 to 18.1 times.

Damage progression in fibre reinforced polymer composites subjected to low-velocity repeated impact loading

In this paper, the authors focused on an investigation of an influence of impact energy and type of impacting tip on the resulting damage and its propagation under repeated impact loading in glass fibre-reinforced polymeric composites. The obtained results allowed for the evaluation of fracture mechanisms during such a type of loading and, based on experimental results two models of overall damage and crack progression were proposed, considering the theoretical fundamentals of damage mechanics. The fitting models were developed in the form of double-exponential functions, which is in a good agreement with phenomenology of the investigated fracture progression as well as experimental data. The three-phase fitting model of structural degradation is confirmed in all the investigated cases and particular phases were attributed to damage progression stages. A variety of the investigated cases and results of fitting of the experimental data allowed to the estimation of fracture mechanisms and propagation character of resulting damage under repeated impact loading. An analysis of coefficients of the fitting models allowed for quantitative description of changes in damage progression for various impact energy and impacting tips considered in the study.

Experimental investigation on reinforced concrete slabs strengthened with carbon textiles under repeated impact loads

AbstractThis study presents the performance of carbon textile reinforcement used as strengthening layers for reinforced concrete (RC) slabs under repeated impact loads. In order to reveal the contribution of carbon textile reinforcement to the behavior of RC slabs under impacts, five identical RC slabs with the dimensions of 1.5 m × 1.5 m × 0.20 m were manufactured and tested at the Technische Universität Dresden. To understand failure mechanisms of RC slabs under impact loadings, two specimens were kept unstrengthened and tested under different impact velocities. The rest of the specimens was strengthened with three different carbon textile reinforcements embedded in an additional 2 cm fine‐grained concrete layer and subjected to impact loads with the same striker velocity. The results observed from the tests revealed that the carbon textile reinforcement is very effective at increasing the impact capacities of the specimens. Additionally, displacement–time histories and crack profiles are highly affected due to the carbon textile reinforcement types and ratios during the impact loadings.

Comparison of Lifetime of the PVD Coatings in Laboratory Dynamic Impact Test and Industrial Fine Blanking Process.

Protective hard PVD coatings are used to improve the endurance of the tools exposed to repeated impact load, e.g., fine blanking punches. During the fine blanking process, a coated punch repeatedly impacts sheet metal. Thus, the coating which protects the punch surface is exposed to the dynamic impact load. On the other hand, the laboratory method of dynamic impact testing is well known and used for the development and optimization of protective coatings. This paper is focused on the comparison of tool life and lifetime of the industrial prepared PVD coatings exposed to repeated dynamic impact load in the industrial fine blanking process and the laboratory dynamic impact testing. Three different types of protective coatings were tested and the results were discussed. It was shown that the lifetime of coated specimens in both the fine blanking and the dynamic impact processes was influenced by similar mechanical properties of the protective coatings. The qualitative comparison shows that the lifetime obtained by the dynamic impact test was the same as the lifetime obtained by the industrial fine blanking process. The laboratory impact test appears to be a suitable alternative for the optimisation and development of protective PVD coatings for punches used in the industrial fine blanking process.

Cumulative damage of hollow glass microsphere weight fraction in polyurethane foam in response to cryogenic temperatures and repeated impact loading

The sloshing impact load of liquefied natural gas (LNG) carriers is an important issue that can cause failure of the insulation system of LNG cargo containment systems, leading to cryogenic leakage from the hull of the ship and generation of boil-off gas. Thus, insulation systems should be designed by considering the repeated impact loading based on the design life as well as the cryogenic temperature. Polyurethane foam (PUF), epoxy resin, and plywood are acceptable materials that can be used to fabricate a typical insulation system to protect the load from the environment. In this study, we investigated the effect of adding hollow glass microspheres (HGMs) to the epoxy resin on the reinforcement of the insulation material. Specimens were fabricated using PUF, plywood, and an HGM/epoxy composite matrix with varying weight fractions of embedded HGM (0, 10, and 20 wt.%). The sloshing impact loads were estimated by the statistical method of the Weibull model, and the top 2% level of the Weibull distribution was selected. The calculated sloshing impact load was 3 J as calculated from the experimental results, and then repeated impact loadings under ambient (290 K) and cryogenic temperature (110 K) were realized in a drop tower facility. To obtain details of the dynamic behavior, microstructural analyses were performed using scanning electron microscopy (to detect the agglomeration of HGM embedded in the epoxy resin). Experimental results show that 10 wt.% HGM showed the best performance in absorption and dynamic behavior. The 10 wt.% HGM specimen also exhibited superior thermal conductivity.

Repeated drop-weight impact tests on self-compacting concrete reinforced with micro-steel fiber

Steel fiber has become a proven material that can significantly alter the behavior of different types of concrete mixtures from brittle to more ductile ones. Rich literature is currently available on the mechanical properties of steel fiber-reinforced self-compacting concrete. However, the investigation of the impact resistance of this material to drop weight is still required to enrich the knowledge about its behavior under different loading conditions. An experimental work was conducted in this research to evaluate the performance of steel fiber-reinforced self-compacting concrete under repeated impact loading using the repeated blows test recommended by ACI 544-2R. The tests investigated the effect of drop weight and drop height in addition to fiber content. Straight micro-steel fibers were incorporated in three volumetric contents of 0.5, 0.75 and 1.0% and were compared with a similar plain mixture. The test equipment was adjusted to conduct repeated impact loading from different drop-heights and using different drop-weights. The adopted drop-heights were 450, 575 and 700 mm, while the adopted drop-weights were 4.5, 6.0 and 7.5 kg. The combination of the adopted drop-heights and weights composes four loading cases in addition to the standard loading case with a drop-weight and drop-height of 4.5 kg and 450 mm. The inclusion of micro steel fiber was found to significantly increase the impact resistance of self-compacting concrete with percentage developments ranging from 150 to 860% compared to plain samples. The specimens tested under 4.5 kg and 450 mm drop weight and height exhibited the highest percentage improvement in impact resistance among the five loading cases. The results also showed that the impact ductility of fibrous specimens was up to 24% higher than that of plain specimens.

Machine learning techniques for estimation of Los Angeles abrasion value of rock aggregates

Rock aggregates are extensively used in the production of materials such as asphalt concrete and Portland cement concrete. Los Angeles Abrasion (LAA) value is one the basic characteristics of crushed aggregates that reflects their resistance against mechanical abrasive factors such as repeated impact loading. There have been several efforts to estimate the LAA value from surrogate physical and/or mechanical properties of the material. Previous works have mainly focussed on a limited number of data samples and thus may not be generalised to make predictions for different lithologies. Another drawback of the current approaches is that they are often in the form of one-to-one correlations between the LAA and a measure of mechanical behaviour such as the uniaxial strength. This paper investigates the capability of Machine Learning (ML) models for prediction of LAA value. Different material properties have been tested as the input parameters to achieve the best prediction results. It was observed that the ML models perform considerably better for predicting LAA compared to the existing correlations reported in the literature.

Adhesion and dynamic impact wear of nanocomposite TiC-based coatings prepared by DCMS and HiPIMS

Nanocomposite nc-TiC/a-C:H coatings exhibit a unique combination of mechanical properties such as high hardness, and low friction and wear. These physical and mechanical properties make those coatings attractive for application in industry. However, the properties of the whole coating/substrate system such as adhesion of the coating to substrate and its response on repeated impact loading known such as dynamic impact wear are also important for industrial applications. Thus, this paper is focused on the adhesion and the dynamic impact wear of nc-TiC/a-C:H coatings prepared by the hybrid PVD-PECVD process. Two series of nc-TiC/a-C:H coatings with a different amount of carbon were deposited onto commonly used industrial cemented tungsten carbide substrates using DC magnetron sputtering (DCMS) and the high power impulse magnetron sputtering (HiPIMS) of a titanium target in argon and acetylene mixture atmosphere. Both series of coatings were analysed using a scratch test and dynamic impact tester with an impact load of 600 N. The HiPIMS prepared coatings exhibited lower thickness and lower thicknesses of the Ti adhesive interlayers between the substrates and coatings than the DCMS prepared coatings. Thus, the adhesion and the impact wear of both series were discussed separately. These properties were discussed with respect to the coating microstructure, phase composition and mechanical properties such as the hardness H, the effective elastic modulus E, and the H/E and H3/E2 ratios. The scratch adhesion of coatings depended on the H3/E2 ratio and coating microstructure, hardness and surface roughness. The impact wear of the nc-TiC/a-C:H coatings depended on the H/E ratio and coating microstructure.

High-Performance Impact-Resistant Concrete Mixture for Transportation Infrastructure Applications

Engineered cementitious composites (ECC) is a class of high-performance fiber-reinforced cementitious composites featuring metal-like strain-hardening behavior under tension and high ductility. The highly ductile behavior of ECC often results in high impact resistance and energy absorption capacity, which make ECC suitable for applications in structures that are prone to impact damages, like exterior bridge girders, bridge piers, and crash barriers. In a recent study, a new ECC mixture has been developed using domestically available polyvinyl alcohol (PVA) fibers and regular river sand in replacement of imported PVA fibers and fine silica sand that are normally used in other ECC mixtures. The newly developed mixture, with improved local accessibility of raw materials, enables structural-scale applications of ECC in transportation infrastructures. To evaluate the suitability of the mixture for impact-resistant structures, in this paper, the tensile and flexural behavior of the newly developed material were characterized under pseudo-static loading and high strain-rate loadings up to 10−1 s−1. Direct drop-weight impact test was also conducted to assess the impact resistance and energy absorption capacity of the material. It was ensured that the ECC mixture maintains high tensile strain capacity above 1.8% under all tested strain rates. Regarding the damage characteristics, energy absorption capacity and load-bearing capacity during repeated impact loadings, ECC was found to have 75% higher energy dissipation capacity compared with regular reinforced concrete specimens and superior damage tolerance. The research results demonstrated that the newly developed ECC has a great potential to improve the impact resistance of transportation infrastructures.