Typical Damage Modes Research Articles

Experimental study on the damage characteristics of steel fiber reinforced concrete slabs attacked by chloride ion under contact explosion

In order to study the damage characteristics of steel fiber reinforced concrete slabs attacked by chloride ion under explosive loading, contact explosion tests were performed for nine pieces of 500 mm × 500 mm × 60 mm slabs. These slabs were divided into three groups based on corrosion time of seawater (uncorroded, corrosion for 10 days, corrosion for 20 days) to achieve different degrees of chloride ion erosion effect. The dynamic response of the steel fiber reinforced concrete slab under contact blast loading were compared and analyzed, and the effects of explosives quality and degree of corrosion were explored. Besides, the propagation characteristics of the stress wave in the slab and the typical damage mode were also studied. The results show that the damage degree of steel fiber reinforced concrete slab has a non-linear increase with the increase of seawater corrosion. Slabs suffer different damage patterns such as cratering and spalling for different qualities of explosives. In addition, based on the experimental results, an empirical formula for predicting the diameter of the blast crater was established.

A physics-based acoustic emission energy method for mixed-mode impact damage prediction of composite laminates

In-service composite laminates are susceptible to impact-induced damage, which can substantially reduce its integrity and service life. The damage prediction remains a great challenge due to mixed damage modes and varying damage patterns. This study develops a novel acoustic emission (AE) energy method for predicting damage areas under three typical damage modes. Laboratory testing of composite laminate specimens subject to quasi-static indentation is performed in conjunction with in-situ AE monitoring to acquire AE data. By bridging two sets of energy formulations developed, namely, the one that correlates the damage area and the released strain energy of each damage mode and another that relates the released strain energy to the AE energy, an analytical model for predicting damage areas using AE energy components is derived. Proper signal procedure procedures are established to extract the energy components from AE monitoring data, and numerical and testing data are used to calibrate the model parameters. The effectiveness of the proposed model is further validated by comparing the prediction results of the damage areas with the actual damage areas of specimens tested under different indentation depths. The result indicates that the proposed AE energy method can yield reliable predictions of the damage area under mixed damage modes.

Effect of electromagnetic force installation method on critically reinforced interference sizes and fatigue behavior of CFRP bolted joints

AbstractThe electromagnetic force dynamic installation (DI) method of interference fit fasteners has significant advantages in improving the quality of the assembly interface of composite structure. This study aims to investigate how improving assembly interface quality may help in achieving high‐precision interference‐fit joints in composites. Single‐lap joint specimens were prepared using electromagnetic installation technique, the fatigue life and failure behaviors of the joints under different bolt‐hole clearances were measured and analyzed experimentally. In addition, a three‐dimensional finite element model was developed to predict the radial pre‐compression stresses around the hole and the progressive failure behavior of various typical damage modes in carbon fiber‐reinforced polymer induced by the interference. The results show that the critical interference range for the DI‐composite bolted structure is 1.0%–1.2%. The fatigue life of the best interference (1.0%) and the worst interference (0%, neat fit) have a difference of 36 times in amplitude. The residual stress with uniform distribution and high amplitude reduces the stress concentration of the hole wall and improves the failure evolution of the loaded hole. The contribution of this study provides vital guidance for improving the fatigue performance of CFRP bolted structures using a novel DI method.Highlights I = 1.0% is the critical damage‐enhancing interference size for dynamically installation interference fit bolts with electromagnetic forces. The residual stress amplitude introduced by the interference does not increase uniformly as the interference size increases. Excessive interference significantly reduces the uniformity and magnitude of residual stresses. Under subsequent cyclic loading, the fifth layer near the inlet and outlet of the extruded lower laminate appears to be the critical ply of extrusion deformation, and severe damage is concentrated in the critical ply of deformation. The decrease of stress amplitude and the variation of mean stress are the mechanisms of fatigue life enhancement in interference fit joints under external cyclic loading.

Experimental investigation of pseudo-ductility in plain weft-knitted epoxy composite laminates under tension

The inherent brittleness of unidirectional fiber-reinforced composites represents a major complication in their broad practical applications. However, exploiting different reinforcement architectures can offer an opportunity for highly desirable ductile fracture nature. This article is aimed at investigating experimentally the tensile behavior of an epoxy laminate reinforced by different layers of plain weft-knitted fabrics. The fabricated laminates were subjected to uniaxial tension in different loading directions, and the corresponding tensile responses were recorded. Basic mechanical properties were characterized and digital image correlation (DIC) was employed to capture surface deformations. Tensile test results demonstrated strong nonlinearity and pseudo-ductility as well as loading-direction dependence in this type of composite laminates. Fracture tests were conducted showing high fracture toughness ranging from 10 to 20 MPa·m1/2. Typical damage modes were characterized using microscopy, which were coupled to a few distinct tensile deformation stages. This work demonstrates that weft-knitted composites are promising in permitting great amounts of pseudo-ductility with clear warning before complete failure. It is also expected to contribute to the understanding of the specific role of weft knit fabrics in composite laminates.

Stress, damage, and fatigue performance analysis of CFRP/Al double-sided countersunk riveted joints with variable rivet-hole clearance

The CFRP/Al countersunk rivet joints are one of the most fatigued dangerous points of the aircraft fuselage. To deeply investigate the failure mechanisms of the riveted joint structures, this paper utilizes electromagnetic riveting technology to prepare single-lap joint specimens and investigates the quasi-static tensile and fatigue failure behaviours of the joints under different rivet-hole clearances and stress levels. In addition, to assist this investigation, a three-dimensional finite element model, combining riveting and fatigue loading, is developed. This model takes into account the strain rate effects during riveting process and progressive failure behavior of various typical damage modes in CFRP laminates. The results indicate that Aluminum alloy sheets fracture dominates the fatigue failure of the joints. Increasing the clearance can reduce the stress amplitude on the shear plane and further enhance the fatigue life of the joints. Furthermore, all additional CFRP damage during the loading process is the growth of the initial riveting damage, and the damage-induced fibre bearing capacity decrease is considered the reason for the increase in stress amplitude of the Al sheet. Last, excessive clearance enlargement does not appreciably diminish the initial riveting damage, instead, it could result in a joint strength reduction.

Applicability of a new composite amusement ride safety device based on acoustic emission monitoring technology

Under the premise of ensuring safety, it is of great significance to realize the lightweight of the non-main load-bearing parts of amusement facilities. The purpose of this study is to study the failure process of a newly designed carbon fiber bumper by using acoustic emission technology. First of all, the design of carbon fiber anti-collision bar can effectively restrain passengers, and its weight is reduced by nearly two-thirds compared to traditional metal materials. Subsequently, the load-bearing capacity of the bumper was tested and acoustic emission monitoring was carried out. The test results show that this new type of combined structure of amusement facility has high reliability, which exceeds the safety factor of 3.5 required by the steel structure of amusement facility. In addition, Renyi entropy was used to select the best window function of short-time Fourier transform, and the frequency domain characteristics of acoustic emission signals of typical damage modes were discussed through appropriately selected windows function. A classifier based on supervised machine learning is established by combining frequency features and acoustic emission feature parameters. Furthermore, the use of classifiers helps to understand the damage behaviour of composite structures.

Interfacial adhesion properties and debonding mechanisms in rejuvenated asphalt mixtures

The interfacial strength between asphalt and aggregate significantly affects the macroscopic properties of rejuvenated asphalt mixtures. Investigating the interfacial properties of rejuvenated asphalt mixtures contributes to understanding the adhesion mechanisms and debonding behavior, enhancing the service life of rejuvenated asphalt mixtures. In this study, molecular dynamics methods were utilized to construct interface models of virgin, aged, and rejuvenated asphalt-aggregate systems, subsequent to which asphalt-aggregate interface pull-out tests were conducted. The findings revealed that the exponential-type cohesive zone model (CZM) effectively characterize the stress-strain correlations during asphalt-aggregate interface pull-out tests. The combination of adhesive and cohesive failure is the typical damage modes at asphalt-aggregate interface. Cohesive failure tended to be the main failure mode between aged asphalt-aggregate interface, while asphalt oxidation aging notably reduced the interface tensile strength and hence the cracking resistance of asphalt mixtures. The interface failure patterns between rejuvenated and virgin asphalt were similar, demonstrating an adhesive failure at lower temperatures and a shift towards cohesion failure at higher temperatures. The interface failure usually occurred at lower temperatures especially for aged asphalt, while the incorporation of rejuvenator could effectively mitigate the cracking potential asphalt mixtures. This study simulated the interfacial failure behavior for rejuvenated asphalt mixtures, which can be a theoretical basis of using rejuvenator in recycled asphalt mixtures.

Seismic performance loss evaluation of reinforced concrete frame structure based on updatable damage model

AbstractAs structural seismic damage develops, the internal force transfer and damage weight relationship of component are constantly changing, and the fixed weighted coefficient is adopted by the traditional weighted method, which cannot reflect the changes in the structural damage state. The structure is a network formed by connecting a large number of components, and the network state undergoes complex changes with the development of component damage. In this paper, a novel method for component damage transfer to structural seismic performance loss is proposed using network shortest paths. First, a directed weighted complex network based on force transfer direction and component stiffness is constructed for reinforced concrete (RC) frame structures. Then, the component damage is calculated by the degradation of its stiffness and is used to update the weight distribution of the damage network. Finally, the structural performance loss is evaluated by the degradation of damage network efficiency. Results show that the proposed method with an updated component weight relationship is able to reflect the true loss of structural performance according to the finite element dynamic elastic‐plastic analysis of RC frame structures. For the structural performance loss degree (none, slight, moderate, severe, complete), the proposed method and the weighted method both exhibit high accuracy (number correctly classified/total number of samples) when structural performance loss is none, severe, or complete loss. The accuracy of the proposed method is significantly higher than that of the weighted method when structural performance loss is slight and moderate loss, with 58.1% and 84.2% improvement, respectively. For structural typical damage modes (global, local, and weak layer damage mode), the proposed method and the weighted method both exhibit high accuracy when structures exhibit global damage mode. The accuracy of the proposed method is significantly higher than that of the weighted method when structures exhibit local and weak layer damage mode. The accuracy of the proposed method is stable at 95.2%, while the accuracy of the weighted method is 76.2% and 70.2%, respectively. Overall, the weighted method exhibits high accuracy when structural performance loss is less than slight loss or greater than moderate loss, while the proposed method exhibits high accuracy throughout the entire process of structural performance loss, especially in moderate loss.

Investigation on interference and damage behaviours of electromagnetic riveted double-sided countersunk 30CrMnSiA/CFRP joints

Carbon fibre reinforced polymer (CFRP) structures benefit from electromagnetic riveting (EMR). However, incorrect riveting parameters could result in damages in CFRP structures during the EMR process. Excessive interference size may introduce initial damages to the joints. As a result, in this paper, the damage behaviours and the interference characteristics of the 30CrMnSiA/CFRP double-sided countersunk electromagnetic riveted joints are investigated. The riveting damage experiment was conducted, with the regular pressing riveting (RPR) process as a comparison. Moreover, a progressive damage FE model considering multiple typical damage modes of CFRP was developed for EMR damage prediction. The results show that when the rivet-hole diameter increases by 5% (4.08mm to 4.28mm), the average interference size of the joint under EMR and RPR processes decreases by 41% and 53%, respectively. Double-sided countersunk riveted joint interference size along the rivet axial distribution is not uniform, the CFRP sheet side of the interference size is relatively small. The EMR achieves a tighter, more uniform interference fit, while causing more severe riveting damages to the CFRP structure. Initial riveting damage exhibits a variety of modes, with delamination damage showing most significant sensitivity to rivet hole clearance.

Axial compression behavior of square CFST short column with triangular-corner gap

In order to investigate the impact of the triangular-corner gap between the outer steel tube and the core concrete on the axial compression behavior of square concrete-filled steel tubular (SCFST) columns, this study conducted axial compression tests on 117 SCFST columns and three reference hollow steel tubes. The main test parameters included steel tube thickness, concrete strength, side length of the triangular gap, and axial gap depth. The test results revealed four typical damage modes in the SCFST columns with triangular-corner gaps. The presence of the gap defect had a significant effect on the ultimate bearing capacity of the SCFST columns, causing a decrease in the range of 1.66 %–17.72 % when the gap ratio ranged from 0.45 % to 12.50 %. Moreover, the influence of the gap ratio on the ductility and initial stiffness of the SCFST with triangular-corner gaps was dependent on the concrete strength and the steel tube thickness. Finally, a simplified formula for calculating the ultimate bearing capacity of SCFST columns with triangular-corner gaps was proposed based on the test data and force analysis. The maximum error between the theoretically calculated value and the test value is within 15 %.

Manufacturing and flexural testing of woven lattice sandwich-ply laminate composites

In this research, single-layered, double-layered and three-layered woven lattice sandwich-ply (WLS) composites were designed and manufactured. Bending experiments were performed on the clamped and simply-supported WLS panels. The effects of multi-layered construction and boundary constraints on flexural behaviors were investigated. Typical damage modes of core fracture, face shear fracture and bending fracture of the panels with four constrained ends, and those of core shear, compression, fracture and face fracture of the panels with two constrained ends were revealed. It is clear that the multi-layered construction can significantly improve the strength, stiffness, and energy absorption. Boundary constraint affects the deformation characteristics, but it will be suppressed as core shear stiffness increases.

Hybrid ratio optimizations on ballistic penetration of carbon Kevlar UHMWPE fiber laminates

Fiber hybrid is a promising strategy for improving ballistic penetration behaviors of fiber-reinforced laminated composites. Ballistic impact performance of hybrid fiber laminates against projectiles depends on various parameters not only with respect to the material properties, fiber types, yarn properties, fabric structures of the constituent plies but also with the hybrid configuration, material combinations and stacking sequences. It has a substantial growth demand to obtains the optimal hybrid design of the fiber hybrid composites, for maximizing the potential of the constituent materials and improving the overall anti-impact performance of the hybrid composites. However, the effect of the hybridization ratios on ballistic penetration behaviors of the hybrid composites is still infant. Here we report the hybridization ratios on ballistic impact damage of carbon/Kevlar/UHMWPE (ultra-high molecular weight polyethylene) hybrid laminates through ballistic impact experiments and three-point bending tests. The fiber hybrid laminates with different hybrid ratios had been fabricated and studied under the impact of FSP (fragment simulating projectiles). The effect of the hybridization ratios on the flexural behaviors, ballistic curves, energy absorptions and damage modes were investigated. The FEA (finite element analysis) was carried out from meso- to macro- scale model. We found that the flexural behaviors are related to the material properties and mechanical balance among different material components in the hybrid systems. The damage modes for various hybrid ratios have a typical impact damage mode like matrix cracking, fiber breakage and delamination. A rational accuracy in residual velocities and damage modes can be obtained between ballistic experiments and FEA results. The hybrid ratios would affect the stress wave propagation in the composites with a gradual attenuation development and lead to different failure mechanisms. This study is expected to reveal a fundamental failure mechanism for the fiber hybrid composites incorporated with three different fiber combinations in different hybrid ratios under ballistic impact. The results can provide important theoretical basis and experimental reference for designing and developing hard multiphase anti-impact composite structures.

Research onthedelamination damage algorithm offiber reinforced composites

Aiming at the typical delamination damage mode of fiber-reinforced composites, the constitutive model and failure criterion of composites that commonly used in dynamic simulation are studied, and the principles and characteristics of cohesive element and tiebreak contact algorithm are analyzed.Then the simulation calculation of two fiber-reinforced composite targets anti penetration is take as an example,The accuracy of the cohesive element and the tiebreak contact algorithm are verified respectively, and the protection mechanism of fiber-reinforced composites in the process of anti penetration is revealed, which provides an important reference for the development and design of new composite protection structures and equipment.

Seismic performance of stone supported traditional timber frames with or without cap beams

Traditional timber frames in East Asia rest on stone bases, and are uncapped or capped with flat timber beams on their top. This study quantified the influence of the cap beam on the seismic performance of stone supported traditional timber frames. Four column foot and head joints were half-scale fabricated and reversed cyclically tested. Typical damage modes of the joints were identified. Methods were proposed to characterize the joints' rotational behavior. Finite element models of stone supported traditional timber frames with or without cap beams were developed. Lateral performance analysis was conducted on typical full-scale frames based on the developed models; fragility analysis was further performed to evaluate the full-scale frames' seismic performance. The tests indicated that the column foot joints were self-centering and had minor residual parallel to grain deformation. However, the column head joints were found with the embedment deformation at the cap beams, resulting to the pinching of their moment-rotation hysteretic curves. By use of existing hysteretic models in OpenSess whose parameters expressed by the theoretical maximum moment and elastic rotational stiffness, the joints’ rotational behavior was well captured. The numerical study indicated that the cap beam significantly increased the lateral performance and deformability of a frame. The elastic stiffness, lateral load-resisting capacity and cumulative energy dissipation of the frame increased by 77%, 81% and 42%, respectively. Fragility analysis indicated that the cap beam increased more than 33% and 23% of the PGAs corresponding to 50% probability exceedance under life safety drift limit and collapse prevention drift limit, respectively.

Damage characteristics and dynamic response of steel–concrete-steel composite targets penetrated by a rigid projectile

Steel–concrete–steel (SCS) composite structures have a good load-bearing capacity and are widely utilized in engineering construction. To investigate the penetration resistance of SCS composite structures, rigid projectile impact target tests of SCS composite targets were carried out. In this paper, the damage characteristics of SCS composite targets were obtained by using shape-measuring and three-dimensional scanning imaging techniques. The dynamic responses of the composite targets were recorded by using strain sensors and acceleration sensors. The results show that the damage degree of steel plates and concrete attack surfaces of the SCS composite structure targets were proportional to the impact velocity of the projectiles. In contrast, the crater formation on the concrete backside was the worst when the collapse occurred. According to the target damage characteristics, the typical damage modes of the SCS composite target for three typical impact velocities were determined. Besides, by comparing the energy consumption of the projectile in the process of penetrating the SCS target with different steel plate combination forms and the concrete target, it was found that the SCS target with the combination form of 3 mm + 4 mm had better anti-penetration performance.

Influence of support interface on the lateral performance of rocking columns in traditional Chinese timber structures

This study investigates the influence of support interface on the lateral performance of rocking columns in traditional Chinese timber structures. Six half-scaled timber column specimens, characterized by stone bases or timber bases, were reversed cyclically tested. Typical damage modes were identified, the load–displacement curves of the specimens were evaluated and compared with those of rigid rocking bodies. Theoretical analysis was further conducted based on a trilinear model. The experiments indicated that with the decrease of support stiffness, the damage mode of timber rocking columns shifted from slight parallel to grain deformation at column bottom to significant perpendicular to grain deformation at timber beams. The support stiffness significantly influenced the lateral performance of timber rocking columns. The peak load of a column resting on a stone base was about 80% of that of corresponding rigid rocking body, the column’s hysteretic loops overlapped each other with strength degradation coefficients greater than 0.95. However, with softer timber beams as support, the peak load of a column was reduced to 46% of that of corresponding rigid rocking body, the column’s hysteretic curves prominently pinched and the strength degradation coefficient decreased up to 0.1 with the increase of loading amplitude. The model-based theoretical analysis well captured the load–displacement curves of timber rocking columns on stone bases, and it further indicated when calculating the load–displacement relationship of timber rocking columns on timber beams with lower support stiffness, the local compression effect and hardening effect perpendicular to grain should be considered.

Axial Compression Performance of Precast Circular Semi-Continuous Concrete-Filled Steel Tube Columns: Finite Element Analysis and Theoretical Modeling

A new finite element (FE) model was constructed with ABAQUS, and the applicability of the model was verified by the coincidence with typical damage modes and load-compression curves in the tests, and the axial compression performance of the precast circular semi-continuous concrete-filled steel tube (PCSCFST) columns was investigated. The effects of diameter-thickness ratio, slenderness ratio, yield strength, etc. on the axial compression performance of the PCSCFST columns were investigated by parametric analysis. The changes in slenderness ratio, yield strength and diameter-thickness ratio of the upper and lower steel tubes have obvious effects on the bearing capacity of the specimen, while the changes in bolt diameter and diameter-thickness ratio of the outer steel tube have little effects on the bearing capacity. In particular, the diameter ratio of bolt to steel tube (d/D) increases to 1/10, the bearing capacity increases slightly, the ratio (d/D) continues to increase until the bearing capacity decreases slightly, and the bearing capacity appears to increase significantly after the ratio (d/D) reaches 1/7; the yield strength ratio of bolt to upper and lower steel tube (fyb/fy1) increases from 1 to 2, the bearing capacity decreases slightly, and the bearing capacity increases significantly when the ratio (fyb/fy1) reaches about 2. After that, the change is minimal. In addition, a theoretical model was developed to predict the ultimate bearing capacity of the PCSCFST columns, and a close correlation was found between the FE simulation results and the theoretical model. The mean ratio of the FE ultimate load Nu,FE to the predicted ultimate load Nu,pre was 1.006 with a standard deviation of 0.0389.

Fatigue performance analysis of SiCf/Ti composites under spectrum load

In this study, the fatigue mechanical properties of SiCf/Ti composites under a spectrum load were investigated, and a spectrum load fatigue test of SiCf/Ti composites was carried out, followed by an analysis of the failure mechanism. The evolution law of typical damage modes involving fiber breakage, matrix cracking, and interface wear with the number of spectrum load cycles was investigated with the establishment of a fatigue damage model for each damage under spectrum load. In the combination of the meso-mechanical model and fatigue damage model, the fatigue hysteresis loop, residual stiffness, and residual strength were simulated and compared with practical experiments.

The behavior of interlocked ortho-grid composite sandwich structure subjected to low-velocity impact

The concept of interlocked ortho-grid core was very attractive, due to great mechanical properties, low cost, and simple processing. However, the rib intersection aroused by this interlocking method was always the weak link where stiffness reduction and failure initiates occurred. In this paper, the low-velocity impact behaviors of the interlocked ortho-grid composite sandwich structure with two typical impact positions and three impact energy were designed and studied experimentally and numerically. The best match relationship between the adjacent ribs was revealed and mainly discussed considering three heights of slot. Besides, the different typical damage responses and damage modes were also observed and discussed. At the impact position of rib intersection, this sandwich structure exhibited a progressive crushing damage, and the prominent damage mode was matrix fracture. The interlocked method with slot using half of rib height represented the best match between adjacent ribs compared with others, illustrating the best impact bending stiffness. A refined finite element model based on progressive damage was established to research the damage mode and sequence, which was not observed at experiments. The present study provided a series of experimental and numerical results, which could be utilized as design reference guidance in the designing of light-weight structures.

Vibration-modelling-based fault feature analysis for incipient damage identification of sun gear

Different types of incipient damage to gears need to be distinguished for the reliable and safe operation of mechanical equipment. However, the identification of various types of incipient gear damage is still a challenge for the fault diagnosis of planetary gearboxes. To identify the various types of incipient damage in a sun gear, fault feature analysis is conducted for various damage conditions in a planetary gearbox. First, the internal excitation aroused by gear damage is computed and the effects of the typical damage modes of a sun gear on the internal excitation are demonstrated. Then, the internal excitation of the damaged sun gear is applied into the dynamic model of the planetary gear train to simulate distributed damage or local damage. After that, with the vibration responses obtained from the dynamic model, a vibration signal model is proposed to simulate the vibration signals of the planetary gearbox. Furthermore, the vibration signals are analysed over the time domain and frequency domain. The fault features of the planetary gearbox are characterized by using residual signals and variational mode decomposition signals, which are useful for identifying the various incipient damage types of a sun gear. Finally, the simulated results are validated by experimental tests.