Impact Failure Mechanisms Research Articles

Finite element explicit dynamics simulation of an impact cutting mechanism analysis of Populus tomentosa branches

The branch impact failure mechanism has gradually received attention from scholars, along with the application of impact cutting methods in plantation forest pruning. In this paper, the impact cutting failure mechanism of Populus tomentosa branches was mainly studied. The impact cutting process of branches was simulated by using Finite Element Method (FEM)-based explicit dynamics. The stress change and deformation characteristics in the branch failure process were studied. A theoretical model of branch impact cutting mechanism with branch diameter, cutting clearance, and branch angle as the main factors was proposed. The model describes the branch cutting damage process and the changing characteristics of cutting force. A branch failure state equation was proposed to describe the branch impact cutting failure patterns. The forest experiment was conducted to validate the branch impact cutting mechanism and the branch failure state equation. This work fills a vacancy of relevant theory and provides a theoretical basis for the future development of forestry and agricultural equipment using impact cutting.

Study on impact properties of carbon/kevlar fiber hybrid composites

AbstractIn this article, carbon/kevlar hybrid composites were prepared using Vacuum Assisted Resin Infusion (VARI). The sandwich structure with plain carbon weave fabric as the core layer and plain kevlar weave fabric as the surface layer was selected as reinforcement and the solution of epoxy resin and curing agent was selected as matrix. The low velocity impact experiment and compression after impact (CAI) experiment were carried out on the samples at different hybrid ratio and different temperatures, and the mechanical response on the impact loads were analyzed respectively. The results show that the specimen can limit the delamination defect expansion of the surface kevlar fiber as the carbon fiber used as the core layer, which reduce the delamination defect area and improve the impact resistance of the sample. The toughness of the sample improves the brittle failure mode, that is, the sample still has a certain bearing capacity after the load exceeds the maximum strength, the sandwiched composites presents a positive hybrid effect. With the increase of temperature, the matrix was obviously softened, the macromolecular movement in the system was intensified, the three‐dimensional network macromolecular structure of the matrix and the fiber/matrix interface properties were damaged, and the mechanical properties showed an obvious downward trend. As far as the influences of hybrid ratio and temperature on impact behavior of composite are concerned, it lay a theoretical foundation for the industrial application of carbon/kevlar hybrid composites.Highlights The sandwiched structure was used to design the composites, which greatly improves the impact properties of the specimens. The impact properties and compression after impact properties at different hybrid ratios and different temperatures were studied. Based on the hybrid effect and temperature effect, the impact failure mechanism of the sample was analyzed.

Discrete element analysis on impact failure mechanism of “Zhengzhou 7.20” catastrophic flood for coal gangue railway subgrade

Limited research has been conducted on the failure mechanism of coal gangue railway subgrade structures during catastrophic flood disasters, including the impact of varying flood impact heights and load sizes. This study investigates the process and mechanism of coal gangue railway subgrade failure in the coal mining subsidence area, in conjunction with the “7.20” catastrophic flood in Zhengzhou. First, various factors such as impact forms, impact height, flow velocity, water depth, and wave height are considered, and a wave-water flow coupling calculation method is proposed to determine the catastrophic flood load acting on inclined slopes. The maximum impact load calculated is then applied to simulate the impact process of the catastrophic flood using Particle Flow Code 2D. As the flood-related parameters increase, the maximum impact load on the subgrade slope also increases, leading to the breakdown of the subgrade and causing fatal damage. Finally, the failure process of the coal gangue railway subgrade under the impact and scour of a catastrophic flood is divided into three stages: erosion weakening, potential failure surface formation, and overall failure. The main failure mechanisms of each stage are revealed. These research result findings offer valuable insights for the design of railway subgrade reinforcement under catastrophic flood conditions.

Investigation on damage behavior of composite T-shaped stiffened panels under compression after multi-point impact considering impact positions

Considering the randomness and non-uniqueness of the impact damage distribution of composite structures, both experimental and numerical simulation methods are employed to systematically explore the multi-point impact damage and compression-after-impact damage behavior of composite T-shaped stiffened panels under three types of impact positions. Non-destructive testing, and numerical simulation methods are used to examine the morphology of multi-point impact damage. The compression failure process of the impacted specimens and the intact specimens (reference group) is investigated by the electrometric method. In addition, the impact failure mechanism and compression failure mechanism is further studied by combining with the numerical simulation method. The results demonstrate that impact position B (the edge of each stiffener flange), the type of impact damage is more complex, in addition to fiber/matrix damage, it contains skin/stiffener debonding damage/layer fracture damage. Especially layer fracture damage, which significantly affects the compression damage behavior of structures.

Failure mechanisms of asymmetric sandwich panels subjected to low-velocity impact: An explicit wave dominating damage model

Asymmetric sandwich panels (ASPs) with tapered transitions are effective configurations for connecting them with other structural elements. However, fiber reinforced composite panels are susceptible to impact events and thus it is imperative to gain a comprehensive understanding of the impact failure mechanisms of ASPs. This article investigates the failure mechanisms of ASPs subjected to low-velocity impacts experimentally and numerically. Low-velocity impact tests are conducted at two energy levels to induce barely visible impact damage (BVID) and visible impact damage (VID). A non-linear finite element (FE) model is developed to elucidate the damage behavior and failure mechanisms of ASPs. The numerical results are compared with experimental data to validate the FE model. Additionally, a parametric study is undertaken to explore the failure mechanisms of ASPs subjected to penetration. This study also investigates the influence of impactor diameter, impactor angle, foam core thickness, face sheet stacking sequence, and face sheet thickness on impact response through numerical simulations. The reported results hold potential significance for safety design ASPs.

Edge-on impact behaviors of helicoidal fiber arrangement of composite laminates

To improve the low-velocity edge-on impact resistance of composite laminates, a helicoidal fiber arrangement of composite laminates (HFACLs) emulated from the micro-structure of the dactyl club is proposed. A finite element method with the progressive intralaminar and interlaminar damage model is adopted for verifications and investigations. Based on the verified model, the failure behaviors and reinforcement mechanisms of the HFACLs subjected to edge-on impact load are extensively revealed. To explore the effect of the rate of variation of helix angle, three types of helicoidal configurations with different derivatives are designed, including helicoidal-Sinusoidal (HS), helicoidal-Linear (HL), and helicoidal-Exponential (HE). From the predicted results, the HFACLs have a higher resistance load and shallower penetration depth. The maximum increase in resistance load and reduction in penetration depth can reach 50.66% and 26.37%, respectively. The laminate with a slight helix angle (HS laminate) variation rate has better edge-on impact resistance. In addition, the effects of impactor ellipticity and impact kinetic energy on edge-on impact response are studied. This study deepened an understanding of the edge-on impact failure mechanisms of the composite laminates and provided a design guideline for the edge-on impact-resistant design of composite laminates.

Evaluation of impact response of thermal-damaged FRP-RC slabs: Effects of FRP bar type and concrete cover thickness

The purpose of present study is to investigate the impact response of FRP-RC slabs under elevated temperatures. Considering the high-temperature degradation effect and strain rate enhancement effect of FRP bars and concrete materials, a numerical model for studying the fire and impact resistance of FRP-RC slabs was established and verified. The impact failure mechanism of in-fire thermal-damaged FRP-RC slabs was analyzed. The influence of the type of FRP bars, concrete cover thickness and fire duration on the in-fire impact resistance of FRP-RC slabs was revealed. Ultimately, the post-fire residual bearing capacity of the slabs after elevated temperature and impact was obtained. The results show that the typical local punching failure mode is not affected by thermal damage while energy dissipated by concrete accounts for most of the impact energy absorbed by the slabs. When exposed to fire for 60 min, the elevated temperature significantly deteriorates the impact resistance of FRP-RC slabs with a cover thickness of 15 mm. At this time, the greater the concrete cover thickness, the better the impact resistance of FRP-RC slabs. Under the combined action of elevated temperature and impact, Carbon FRP-RC slabs have greater stiffness, lower deflection, greater impact plateau value, less impact duration and lower energy consumption than Aramid FRP, Basalt FRP and Glass FRP-RC slabs. Moreover, the damage index of the slab based on residual bearing capacity and peak displacement is approximately linearly positively correlated. The influence of the concrete cover thickness is more prominent on the damage index based on the peak displacement.

Comparative analysis of impact failure modes between slotted rock and intact rock

The compression effect of geostatic stresses and hydrostatic pressure on rock increases with the depth of geothermal well, which strengthens the rocks and reduces the rate of penetration (ROP). How to overcome the strengthening effect of stress on rock and weakening rock drillability has become a key factor to improve drilling speed. Based on a novel method for improving the rate of penetration in deep drilling by employing ultra-high-pressure water jets to create peripheral groove at the bottom of the hole, which could release in-situ stresses and consequently weaken the hard-to-break zone at the periphery of the bottom hole. By lab test and numerical simulation, main factors are analyzed to investigate the effects of slotted granite and slotting characteristics on failure mode, backward impacting energy, and impact force under the condition of bottom hole stress. The results reveal that the presence of grooves prevents the energy needed to break rocks from being transferred to the far field area. Instead, the stress wave reflects within the rock between the grooves, leading to tensile failure and a significant increase in the number and area of cracks inside the rock. Additionally, the specific energy exhibits greater sensitivity and a 64% reduction as the groove depth increases from 5 to 15 mm. Moreover, the backward impacting energy decreases gradually with the increase of groove depth, and when the groove depth reaches 15 mm, almost no backward impact energy is generated, and the impact force decreases by 51%. Furthermore, Groove depth has the dominant impact on rock failure, not only increases the internal crack density inside the rock, but also the occurrence of blocky rock masses facilitates more easily. the deeper the groove, the more significantly the blocky rock masses. The research could provide an effective means of reducing backward impact energy and increase the ROP for deep drilling, while also expanding the understanding of the impact failure mechanism of rocks.

Low velocity impact failure mechanisms of carbon/UHMWPE 2.5D woven hybrid composites via experimental and numerical methods

This paper investigates the failure mechanisms of carbon/UHMWPE 2.5D woven hybrid composites under single and repeated low velocity impacts. Two types of specimens, carbon 2.5D woven composites (C-2.5DWC) and carbon/UHMWPE 2.5D woven hybrid composites (H-2.5DWC), were subjected to single and repeated impacts at 15 J/mm and 5 J/mm respectively. X-ray micro-computed tomography was employed to discuss the damage distribution. A meso-macro combination finite element model was proposed to analyze the failure mechanisms. The results demonstrated that, when compared to C-2.5DWC, H-2.5DWC has higher specific energy absorption and distinct toughness characteristic under 15 J/mm single impact, and exhibits a more dispersed damage distribution that primarily extends along the weft direction as the number of 5 J/mm repeated impacts increases, resulting improved damage tolerance. The simulation results agreed well with experimental data, and the synergistic effect of carbon and UHMWPE fibers allows uniform propagation of the impact stress within hybrid composites.

Single-Impact Failure of Multi-Layered Automotive Coatings: A Finite Element-Based Study

Automotive coatings are a multi-layered polymer composite structure whose impact resistance is closely related to the appearance and safety of a vehicle. Since experimental methods are of high cost and poor repeatability, in our work, a finite element model is developed for the single-impact failure of automotive coatings. In this model, a multi-mechanism damage model and a large deformation cohesive zone model are employed to account for the polymer-ply and interlaminar failures of the coating, and some rate-dependent material models are adopted to capture the effect of impact velocity. The simulated results indicate that the proposed model can reproduce the failure patterns of automotive coatings well. In addition, the impact failure mechanisms of the coating are revealed. Numerical findings show that both brittle and ductile failures are found in the coating and there are three stages for the propagation of the delamination crack. Finally, we numerically investigate the effects of primer mechanical properties, i.e., Young’s modulus, yield strength, and re-hardening modulus, on the impact resistance of automotive coatings. Our work is helpful to the design of coating, which can improve the impact resistance of automotive coatings.

Comparison of stacking sequence on the low‐velocity impact failure mechanisms and energy dissipation characteristics of CFRP/Al hybrid laminates

AbstractCompared with the resin‐based composite laminates, fiber metal laminates (FMLs) have superior impact resistance. In this study, investigations were made to reveal the effects of stacking sequence on the low‐velocity failure mechanisms and energy dissipation characteristics of carbon fiber reinforced plastics (CFRP)/Al hybrid laminates with same areal density. Experiments were carried out to characterize the typical mechanical responses. Failure morphologies were evaluated by X‐ray computed tomography scanning techniques. Then numerical simulations based on three‐dimensional progressive damage analysis were applied to reveal the dynamic evolution process and energy dissipation characteristics. Results indicated that plastic deformation of aluminum layers acted as the dominant factor in energy dissipation. Stacking aluminum layers on the exterior surface could increase the absorbed impact energy and reduce the fracture behavior of the component layers. The specimens with more CFRP layers stacked on the surface exhibited more severe fracture behavior of component layers and larger delamination areas, thus promoting the energy dissipated by CFRP cracking and delamination. This work intended to provide practical guidance for the structural design of fiber reinforced polymer/metal hybrid protective structures.

Elastic-plastic progressive damage model and low-velocity impact failure mechanism of composite materials

An elastic-plastic progressive damage model (PDM-3DEP) was proposed to study the mechanical response and damage development of composite laminates under low-velocity impact. The 3D Hashin failure criterion and an improved three-dimensional damage evolution model that considers strain component of ε33 and shear stain are implemented to describe the initiation and evolution of damage modes. The zero-thickness cohesive elements which follow bilinear traction-separation law are applied to simulate delamination. The numerical and experimental mechanical curves and damage distribution of composite laminate with a stacking sequence of 03o/45o/−45oS were compared to verify the proposed PDM-3DEP. The consistent results of the numerical and experimental data indicates that the proposed method can accurately describe damage mechanical behavior under low-velocity impact. Moreover, another type of composite laminate with a stacking sequence of 02o/902o/02o/902o/02oS is adopted for further verification. It is concluded that the proposed model can accurately analyze the mechanical responses of different composite laminates.

Experimental study on the mechanical properties and impact behaviors of entangled metallic wire material under repeated low-velocity impacts

Repeated impacts occur frequently and the damage to its structure cannot be underestimated in national defense weapons and equipment. In this article, the mechanical properties and impact behaviors of entangled metallic wire material (EMWM) with different relative densities under repeated low-velocity impacts were investigated via a series of mechanical tests. Each EMWM specimen was subjected to an impact test of 6 m/s each time, and the test was repeated ten times. Experimental results show that with the increase of the number of impact cycles, the damage of EMWM progressively intensifies, the impact stiffness increases, and the energy absorption rate decreases. The mechanical properties of EMWM with higher relative density are more stable under repeated impacts, it displays stronger repeated impact resistance, and it is suitable to withstand repeated impacts. After reaching a certain number of impact cycles, the energy absorption rate tends to be stable. The energy absorption of the EMWM mainly comes from the dry friction between the adjacent wire helixes, the plastic deformation of EMWM, and air damping. Moreover, the impact failure mechanisms of EMWM under repeated low-velocity impacts were described. The electron microscope photos show that the EMWM specimen has no obvious damage after repeated impacts, and it has good repeatable impact ability.

Study on abrasive particle impact modeling and cutting mechanism

AbstractAbrasive water jet impact is widely applied in processing, oil fracturing, coal mining, rock crushing, and other engineering fields. The influence of abrasive particles on cutting performance is one of the main characteristics of this technology, which is different from pure fluid cutting. Therefore, as for improving the cutting performance of abrasive water jet, studying the cutting mechanism of abrasive water jet, and clarifying the mapping relationship between particle parameters and cutting, it is of great theoretical and practical significance to clarify the impact failure mechanism and material removal mechanism of abrasive particles in the process of high‐speed impact. In order to study the effect of abrasive particles on cutting performance, irregular abrasive particles are simplified to angular particles and circular particles in this paper. The impact shooting process of particles in abrasive jet cutting is numerically simulated by using smoothed particle hydrodynamics (SPH) method, and the target impact experiments are carried out. The fracture processes of ductile materials and brittle targets impacted by different shapes of particles are studied. The results are showed as follows. Firstly, the SPH numerical model has high accuracy and successfully reproduces the collision process of particles in the process of abrasive jet cutting, including the deformation mechanisms such as plowing, cracking and crushing of the target, and the error of the dent curve formed by the collision is less than 0.5 mm. Secondly, the impact mechanism of angular and circular particles is different for targets with different material properties. For ductile materials, the process of material accumulating to failure value is slow, mainly by the way of accumulation removal. And for brittle materials, it mainly produces plastic deformation and failure, without obvious material accumulation and extrusion area. Thirdly, different impact angles of particles have great influence on material removal.

Experimental study on the low-velocity impact failure mechanism of foam core sandwich panels with shape memory alloy hybrid face-sheets

Abstract Superelastic shape memory alloy (SMA) as an advanced smart material has been used to improve the impact performance of fiber-reinforced composites in recent decades. Due to the low impact toughness of the thin composite face-sheet and the poor strength of the foam core, sandwich panels are sensitive to the transverse loading. SMA fibers were embedded into the composite laminated to improve the impact resistance of the traditional foam core sandwich panel in this work. Five new types of SMA hybrid panels were prepared, and the testing panels with penetration failure were observed at the impact energy of 50 J. The impact mechanical responses and the damage morphology were analyzed, and the impact failure mechanism was also revealed. Results show that all sandwich panels were failed, the fiber breakage occurred at the impact region in the traditional panels, while part plies of the rear face-sheets split-off in the SMA hybrid panels. The impact performance of the SMA hybrid panels is improved when compared with the traditional panel, the reduction of the delamination area by 48.15% and the increase of the load-bearing threshold by 32.75% are acquired for the hybrid sandwich panel with two layers of SMA fibers in the rear face-sheet.

Near-fiber nanomechanical mapping and impact failure mechanism of 3D braided composites subjected to thermo-oxidative environment

The macroscopic mechanical behaviors generally correlate with nanomechanical properties, especially elastic modulus. This paper presents the thermo-oxidative ageing effects on nanoscale elastic modulus and impact failure mechanism of 3D braided composites at micro and macro levels using PeakForce Quantitative Nano-Mechanics (PF-QNM) and digital image correlation (DIC) technologies. The values of nanoscale elastic modulus of near-fiber resin pocket were about three times than that of global modulus in neat resin under low-velocity impact compression (LVIC) loading. However, the modulus retention rates were consistent which was ∼88% after ageing for 16 days at 180 °C. The decline of them has provided a direct evidence for resin degradation after ageing. In addition, the in-plane impact failure mechanism of braided composites mainly contained five modes, i.e., matrix cracking, interface cracking, matrix fracture and peeling off, fiber buckling and slipping, and fiber breakage. Thermo-oxidative ageing only changed the crack propagation path but not the damage modes.

Development and impact characterization of acrylic thermoplastic composite bicycle helmet shell with improved safety and performance

Fiber-reinforced composites are increasingly used as an outer shell of sporting helmets as an alternative to conventional thermoplastic shells like Acrylonitrile butadiene styrene (ABS), Polyurethane (PU), and polycarbonate (PC) for improved protection. The current research presents a detailed study to manufacture novel woven carbon/Elium® (WEL) thermoplastic composite helmets and investigate the details based on the impact tests following the industrial safety certification criteria (CPSC 1203 helmet certification) tests on the flat, curb-stone, and the hemispherical anvils. The effect of thermoplastic Elium® resin toughened thermoplastic Elium® IM, and Epoxy resin is investigated to understand the benefits offered by the thermoplastic variants in terms of safety, energy absorption, and the impact failure mechanisms. Post-failed Carbon/Elium® thermoplastic composite shells have shown more ductile and less catastrophic damage as opposed to the Carbon/Epoxy composite shell damage. The impact damage mechanisms as observed from the in-situ high-speed camera images have shown more deformation-dominated failure mechanisms for the composite shells manufactured with Elium® and toughened Elium® resin. Carbon/Epoxy composite shells have shown lower energy absorption and the nature of the failure was more catastrophic and more cracks were noticed on the inner side of the foam which is directly attached to the human head. In case of an impact on a flat anvil, the PC shell configuration has shown a critical injury rate of 28.7% and a fatality rate of 6%. With the manufactured Carbon/Elium® composite helmets, the chances of critical and fatal injury rates are reduced to 16.7% and 3% respectively.

Impact failure mechanism and mechanical characteristics of steel fiber reinforced self-compacting cementitious composites containing silica fume

An experimental investigation was performed to study the benefits of partially replacing ordinary Portland cement with pozzolanic material on the fresh and hardened characteristics of high-strength self-compacting (HSSC) cementitious composite reinforced by randomly distributed wavy steel fiber. The four wavy fiber volume fractions (0.25%, 0.50%, 0.75%, and 1%) and silica fume contents of 5 and 15 wt% (wt%) of cement were investigated. A total of fifteen mixtures, including different combinations of the fiber and silica fume, were designed and assessed in terms of the passing ability, water absorption, tensile, compressive, flexural, and impact tests. The energy-dispersive X-ray microanalysis (EDX) was applied to specify the cementitious matrix's chemical compositions quantitatively. Moreover, the wavy fiber’s surface topography in the nano-metric scale was specified using an atomic force microscope. The results reveal that the patterns of cracks, impact energy at first crack and failure mechanism, increment in the number of blows after first-cracks, flexural strength, and splitting tensile behavior of mixtures were greatly influenced by adding wavy steel fibers. It was also found that the improvement in toughness and post-peak behavior of HSSC cementitious composites was appreciably governed by the bridging effect of fibers and an increase in bonding strength of interfacial transition zone between fine aggregate and cement paste due to an increase in the content of silica fume. The benefit of the present investigation is to better understand the failure performance of fibrous self-compacting composites.

Micro-scale impact testing - A new approach to studying fatigue resistance in hard carbon coatings

Improving the fatigue resistance of DLC coatings under highly loaded repetitive contact is an important step to increasing their performance in demanding applications. The nano-impact test has been shown to be effective at highlighting differences in resistance to contact damage in thin hard carbon coatings deposited on hardened steel. A novel micro-scale rapid impact test capability capable of producing repetitive impacts at significantly higher strain rate and energy than in the nano-impact test has been developed recently enabling the study of coating fatigue with less sharp spherical indenters than in the nano-impact test.Results with the new micro-impact technique on two commercial hard carbon coatings (Graphit-iC and Dymon-iC from Teer Coatings) on tool steel are presented. The role of coating mechanical properties on the fatigue resistance and the load-sensitivity of the impact failure mechanism is discussed. The harder coating with higher sp3/sp2 bonded C (Dymon-iC) was found to be significantly less durable under fatigue loading than the softer Graphit-iC. Reasons for the observed differences are discussed.

Layup structure effect on the composite laminate impact resistance: experimental and finite element studies

Four kinds of sandwich laminates with different layup structures and same thickness are designed and fabricated by autoclave and heat pressing process respectively. The impact tests of four composite laminates were carried out to compare the impact resistance of composite laminates with different ply structures. The impact finite element model is established, and the impact process is simulated by the finite element method. To some extent, the impact failure mechanism of composite laminates and their impact failure results have been obtained.