Cumulative Damage Mechanism Research Articles

Cumulative damage effects of repeated underwater explosions on multi-cabin structures

This paper presents experimental and numerical findings regarding complex multi-cabin structures with the goal of elucidating cumulative damage mechanisms and assessing the influence of blast distance on damage characteristics under repeated underwater explosions. The damage characteristics of a multi-cabin structure were analyzed through single and repeated explosion tests employing equal-mass charges. The shockwave loads and structural damage observed during testing were accurately predicted through numerical simulations, which revealed that the structure experienced the combined impact of shockwaves, transmitted pressure waves, and bubble expansion loads during repeated explosions. The findings demonstrate that repeated underwater explosions produce a cumulative damage effect, leading to a significant increase in the extent of depression plastic deformation and deflection of the structure. However, the gain in cumulative damage effects is limited compared to a single explosion with an equivalent charge. A single explosion results in extensive tearing and dent deformation of the structure, causing far more severe damage than repeated explosions.

Numerical Study on the Dynamic Response and Damage Cumulative of Bolt-Supported Cavern under Adjacent Cyclic Explosion

Adjacent cyclic explosions significantly impact the stability of underground anchored caverns. Based on the similar model test of the vault explosion of the anchored cavern, the dynamic analysis finite element software ANSYS/LSDYNA(18.0) was used to establish a model of the straight wall side explosion of the underground anchored cavern and conduct a numerical simulation. When the total amount of explosion load is the same, we compared the stress time history curve, displacement time history curve, tunnel wall displacement, and circumferential strain curve of the surrounding rock in the underground anchored cavern (under both a high-level single-side blast and a low-level cyclic side blast). We obtained the dynamic response rules of the surrounding rock. By comparing the damage evolution process of the surrounding rock in the two situations, the damage accumulation law of the surrounding rock was analyzed. At the same time, the axial stress distribution characteristics of underground anchor cavern anchors under the action of cyclic explosion were studied. The findings demonstrate that when the total level of blast load adjacent to the cavern is the same, the displacement and circumferential peak strain of surrounding rock and the axial stress of rock bolt in the high-level single explosion are greater than those in the low-level cyclic explosion. However, compared to a single explosion, the rock mass suffers more damage in the cyclic explosion. This study will provide engineers with information that will assist them with a better understanding of the cumulative damage mechanisms of surrounding rock, as well as the stress characteristics of rock bolts under dynamic loads near the explosion site, which will be used to design underground caves with anti-blast features.

Dynamic response and cumulative damage mechanism of simplified hull girders under repeated underwater explosions

The dynamic response and cumulative damage mechanism of simplified hull girders (SHGs) subjected to repeated underwater explosions were investigated in this research. Experimental and numerical investigations were conducted to gain a comprehensive understanding of the relationship between cumulative damage and explosive charge. Three series of experiments were carried out on SHGs, subjecting them to both single and repeated loading (up to five times). The analysis focused on the overall deflection values of the SHG and the local bottom plate deflection values, revealing a linear relationship with the cumulative number of occurrences. A validated finite element simulation model was employed to examine the response of the SHGs under repeated blast loading, utilizing experimental results for validation. An impact factor was established to quantify the magnitude of the explosive force, considering both the power of the explosive and the distance of detonation. The SHGs showed localized deformation at 10 impact factors, but experience pronounced cumulative effects at 14.4 and 20 impact factors. Furthermore, a consistent decline in the residual strength of the SHGs as the number of explosions increased. Following the first underwater explosion, the damaged SHG displayed an ultimate plastic bending moment of 3696.5 N m, reflecting a 16.3 % reduction compared to the unloaded SHGs. This reduction can primarily be attributed to the altered load distribution on the deformed SHGs. These findings contributed to the understanding of the cumulative damage behavior and response of SHGs exposed to repeated underwater explosions, providing valuable insights for the design and structural integrity assessment of naval vessels.

Damage mechanisms of a typical simplified hull girder with thinner plates subjected to near-field underwater explosions

Investigating the responses of simplified hull girder (SHG) structures subjected to underwater explosions can yield valuable research insights for real ships. However, previous literature experiments predominantly utilized SHGs with plates of large relative thickness. To examine the ships’ damage mechanisms, an underwater explosion experiment is conducted on an SHG with plates that closely approximate the relative thickness of those in real ships. After verifying the calculation accuracy, simulations of various cases are performed to obtain the response results. The damage mechanisms of the SHGs subjected to underwater explosions are discussed from the perspective of creases. The cumulative damage mechanism in a single underwater explosion is identified. Modes of collapse mechanisms, including hogging and sagging, are summarized, and prediction formulas for estimating the sizes of the core damage zone are provided. The results indicate that the damage phenomena on the thinner-walled SHG are more complex, resemble those observed in real ships, representing the evolution types from previous studies. For the SHG configuration employed, the hogging crease collapse mechanism exhibits an M-shaped pattern, while the sagging crease collapse mechanism displays a W-shaped pattern. The provided prediction formulas enable a quick estimation of the core damage zone size.

Theoretical and experimental analysis of the correlation between magnetic memory signals and cumulative ductile damage of butt weld under low cycle fatigue

Welded structures experiencing superimposed cyclic loads with large plastic strain during a strong earthquake can easily lead to ductile or fatigue fracture. A newly developed self-magnetic flux leakage (SMFL) nondestructive detection technology named metal magnetic memory (MMM) is a valid approach to monitoring the development of fatigue damage in ferromagnetic materials. To investigate the correlation between MMM signals and cumulative ductile damage for butt weld under low cycle fatigue (LCF), combining strain-based Jiles-Atherton hysteresis model, magnetic charge model, and cumulative damage mechanics model, the theoretical relations between normal component HSF(z) of MMM signals and cumulative ductile damage D for single V groove butt weld were established in this paper. Relevant monotonic tensile tests and strain-controlled LCF tests were conducted, and the HSF(z) signals on the surface of welding specimens under different cyclic loads were measured. Comparing with experimental results verified the feasibility and accuracy of the theoretical relations. The results indicated that the peak-valley gradient Kp-v on the HSF(z) signals curve was decreased monotonously as the cumulative ductile damage D increased and the rate of decrease also diminished gradually. A possible exponential descending tendency of Kp-v with increasing D was demonstrated. Besides, the influences of weld width and weld reinforcement on the correlation between Kp-v and D were discussed theoretically in detail. This research provided a potential possibility for the assessment of the cumulative ductile damage at the welding joints under LCF based on MMM technology.

Low-cycle fatigue behavior on the tensile region of Hollo-bolted angle connections

This paper presents the results of an experimental program to evaluate the low-cycle fatigue-related characteristics of the tensile region of Hollo-bolted angle connections. A summary of a total of 40 tension tests of equivalent T-stub connections is reported. The geometric parameters vary with the bolt gauge width, the column wall's thickness, the bolt type, and the angle's thickness. Based on the experimental test results, the typical failure mechanisms, the hysteretic load-deformation relationship, and the response characteristics such as degradations of strength and energy dissipation capacity of the connections are examined. It is shown that the bolt gauge width and the angle's thickness have significant influences on the failure mode. Energy-based model is proposed to overcome certain geometric limitations and five commonly used damage models are used to predict the damage behavior of connections. Moreover, the low-cycle fatigue life test results are compared with the codified S–N curves through a transformation of the displacement range into the effective stress range. Furthermore, the cumulative damage mechanism is analyzed and the fatigue life formula is obtained. Finally, the results are evaluated and verified by regression analysis. The 90% confidence level was used to test the availability of the regression equation, and the equivalent level of fatigue strength of the tensile region of angle connections is not less than Category 40 (ΔσC = 40 N/mm2). The EC3, BS7608, and AISC-LRFD-1999 specifications are used to evaluate the low-cycle equivalent fatigue strength, and it is found that there is a certain safety reserve when using Category 36.

Investigations on the macro-meso cumulative damage mechanism of the discontinuities in soft-hard interbedded rock mass under pre-peak cyclic shear loading

To investigate the macro-meso cumulative damage mechanism of the discontinuities in soft-hard interbedded rock mass, laboratory pre-peak cyclic shear tests and PFC 2D meso numerical calculations under constant normal load (CNL) were carried out, considering the effects of moisture content, normal stress, shear rate, shear amplitude, first-order asperity angle and number of cyclic shear. The curve of the shear stress with shear displacement can be divided into six stages, i.e., initial nonlinear compression-shear deformation, compression-shear deformation of approximate linear elasticity , cyclic shear cumulative damage deformation , compression-shear deformation with slowly rising stress, compression-shear deformation with sharply rising stress and compression-shear deformation of brittle stress drop. The peak (residual) shear strength and cumulative shear (normal) displacement decrease and increase, respectively, with number of cyclic shear increasing under the same moisture content, normal stress, shear rate, shear amplitude or first-order asperity angle; under the same number of cyclic shear, these increase and decrease, respectively, with normal stress or first-order asperity angle increasing, while these decrease and increase, respectively, with moisture content, shear rate or shear amplitude increasing. The curve of the meso cumulative damage crack number (energy) with shear displacement shows the characteristics of a slight increase-steep increase, a slow increase and a steep increase-slow increase-steep increase (crack number) or steep increase-slow increase-steep decrease (energy) in the early, middle and later stages, respectively, while the curve of that with number of cyclic shear shows the characteristics of a steep increase and slow increase in the early and later stages, respectively. The macro experimental observations and meso numerical results are in good agreement, and the typical failure modes of the rock discontinuities were summarized as compaction – crack initiation failure, cyclic dislocation – penetration failure and separation – gnawing failure; meanwhile, the macro-meso cumulative damage cracks are approximately an “inverted U-shaped” and densely distributed near the rock discontinuities.

Investigation on the dynamic cumulative damage mechanism and stability of bedding rock slope under the deterioration of rock mass in the hydro-fluctuation belt

Investigation on the dynamic cumulative damage mechanism and stability of bedding rock slope under the deterioration of rock mass in the hydro-fluctuation belt

Mechanism of cumulative damage to short fiber type C/SiC under tension

Stress–strain relations at different degrees of peak stress were investigated using loading–unloading tests to elucidate cumulative damage mechanisms of short fiber type C/SiC under tension. Damage observations revealed their crack length, number, and angle characteristics. Furthermore, stress–strain relations were estimated by expanding Basista’s equations and by substituting measured damage characteristics into them, which revealed a nonlinear stress–strain relation. Cracks propagated in transverse fiber bundles without fiber fracture, connecting other cracks that had 75 ° – 90 ° orientation to the tensile axis. Stress–strain relations estimated qualitatively and quantitatively suggest that mixed mode I and mode II crack opening in transverse fiber bundles in the through-thickness plane caused the stress–strain nonlinear relations.

Cumulative Shear Damage Mechanism to Short Fiber Type C/SiC

A cumulative damage mechanism for short fiber type C/SiC during shear loading–unloading testing was examined and quantified using Iosipescu specimens parallel in the in-plane and through-thickness plane, and by using modified fracture and damage mechanics theory referring to measured damage characteristics (crack length, number and angle). A nonlinear stress–strain relation was found for both specimens. Decrease in the apparent modulus was confirmed with increased peak stress, although permanent strain increased. Inelastic strain of the decomposed tensile direction derived from shear stress was greater than that of the compressive one. Cracks propagated perpendicularly to the tensile direction, intruding on the boundary of the transverse fibers and connecting to other cracks. The theoretical damage mechanics model succeeded to predict the stress–strain relation, proposing that the shear mechanical properties are predictable by measuring the damage characteristics.

Experimental and theoretical analysis of the correlation between cumulative plastic damage and SMFL of structural steel under low cycle fatigue

Evaluation of fatigue damage is critical for ensuring the safety and durability of steel structures. A newly developed non-destructive testing (NDT) method named magnetic memory method (MMM) is a valid approach to evaluate the ferromagnetic material stress and damage utilizing changes in the self-magnetic leakage (SMFL) field. However, because of the lack of accurate description of the SMFL changing mechanism under elastic and plastic cyclic loads, the application of MMM in the assessment of cumulative plastic damage D for structural steel under low cycle fatigue (LCF) is greatly limited. Hence, in this paper, based on J-A magneto-mechanical theory and J-A magnetic hysteresis theory, an improved theoretical model that described the variation of irreversible magnetization with plastic strain after cyclic loading was proposed and verified. Combining with magnetic charge theory and cumulative damage mechanics model further, the theoretical relationship between the gradient K of SMFL curves and cumulative plastic damage D was established, which indicated preliminarily K had a potential possibility to assess the D. Then, the tension–compression LCF tests on Q345B and Q345qC dog-bone steel sheet specimens were conducted and the surface SMFL of the specimens under cyclic load was measured. The experimental correlation between K and D was further given by the analysis of experimental data and clarified from the perspective of energy conversion for the first time. By the comparison between experimental and theoretical results, and the in-depth analysis of the microcosmic mechanism about the activity and multiplication of dislocation, the semi-quantitative correlation that K was related to D exponentially was presented. The accuracy of the established theoretical relationship was further verified. Thus, the established K-D theoretical relationship can be used for the theoretical analysis of the quantitative characterization of cumulative plastic damage. This work demonstrates that the cumulative plastic damage can be estimated semi-quantitatively via the variations of SMFL curve, which is beneficial for the fatigue damage assessment for structural steel under LCF.

Research on Design Parameters and Fatigue Life of Tunnel Bottom Structure of Single-Track Ballasted Heavy-Haul Railway Tunnel with 40-Ton Axle Load

The coupling calculation model of tunnel and surrounding rock is established by the finite difference method, and the main design parameters of lining structure of single-track ballasted tunnel under 40-ton axle load, heavy train load, are studied in combination with cumulative damage mechanism of surrounding rock at tunnel bottom and the fatigue life characteristics of concrete structure at tunnel bottom. The results show that (1) inverted arch shall be set in sections of III-grade and above. Whether an invert is set in sections of II-grade and below shall be determined according to lithology and groundwater conditions. When the surrounding rock condition is good and the tunnel bottom structure (without invert structure) is adopted, the thickness is recommended to be more than 20 cm, and the concrete strength grade should not be lower than C35. (2) Connection mode: the inverted arch and side wall of the tunnel should be connected in sequence to reduce the stress concentration and improve the stress state of the connection part between the inverted arch and the side wall. (3) It is suggested that the rise-span ratio of invert of single-track tunnel should be 1/6 ∼ 1/8; the larger value should be taken when the surrounding rock condition is poor and the small value should be taken when the surrounding rock condition is good. (4) The thickness of inverted arch is recommended to be no less than 20 cm under the condition of V-grade surrounding rock, to be no less than 15 cm under IV-grade surrounding rock, and to be no less than 10 cm under the condition of III-grade surrounding rock and II-grade surrounding rock sections requiring inverted arch. (5) The recommended value of bedding thickness meeting the design service life is 20 cm under the condition of II-grade surrounding rock.

Cumulative Damage Mechanism of Short Fiber type C/SiC under Compression

This study investigated cumulative damage mechanisms of short fiber type C/SiC under compression. To measure mechanical properties (unloading modulus and permanent strain) before fracture, repeated loading–unloading tests were conducted using a strain gage. Damage was observed to assess characteristics of crack density, length, number, and propagation angle. Furthermore, relations between mechanical properties and damage characteristics were elucidated by application of Basista’s equations and by substituting crack densities inferred from damage observations. Stress–strain relations revealed nonlinear behavior. The unloading modulus did not change, but the permanent strain increased. Cracks propagated mainly between fibers, without fiber fracture, connecting other cracks in the direction of orientation 0 deg to 30 deg to the compressive axis. We estimated permanent strain using Basista’s equations and damage characteristics. Estimates roughly agreed with experiment results, suggesting that the permanent strain increase is attributable to closed crack sliding and friction caused by increased crack density.

Probabilistic S-N fields based on statistical distributions applied to metallic and composite materials: State of the art

Fatigue life prediction of materials can be modeled by deterministic relations, via mean or median S-N curve approximation. However, in engineering design, it is essential to consider the influence of fatigue life scatter using deterministic-stochastic methods to construct reliable S-N curves and determine safe operation regions. However, there are differences between metals and composites that must be considered when proposing reliable S-N curves, such as distinct fracture mechanisms, distinct ultimate strengths under tension and compression loading, and different cumulative fatigue damage mechanisms including low-cycle fatigue. This study aims at conducting a review of the models used to construct probabilistic S-N fields ( P-S-N fields) and demonstrate the methodologies applied to fit the P-S-N fields that are best suited to estimate fatigue life of the selected materials. Results indicate that the probabilistic Stüssi and Sendeckyj models were the most suitable for composite materials, while, for metals, only the probabilistic Stüssi model presented a good fitting of the experimental data, for all fatigue regimes.7

Analysis of Cumulative Damage Failure for Driving Coil in Coilgun

In the launching experiment of a coilgun, the driving coil, including winding and shielding, is always destroyed after several launching times. To improve the service life of a coilgun, the cumulative damage mechanism of the shielding and the fatigue life assessment of the winding are investigated in this paper. First, the electromagnetic field of a coilgun, considering the kinematic influence, is simulated using the field-circuit time-stepping finite-element method. Afterward, the result of the electromagnetic force (EMF) is applied to the structural field as the load to calculate the stress and displacement distributions. In addition, using the static strength assessment, it is determined whether there is a defect in the materials. For the shielding made of a nonmetallic material, if the stress is greater than the ultimate tensile strength (UTS), cracks must emerge. For the winding made of a metallic material, even though the stress is less than UTS, the fatigue failures still occur with the application of repetitive loads. The analysis results of the cumulative failure show that the shielding is destroyed after several launching times. According to the stress-life characteristics (expressed as S-N curves) of the winding material and the analysis results of fatigue, the service life of the winding is much longer than that of the shielding. Finally, a type of insulating material with higher UTS is proposed to improve the service life of the coilgun.

English

This study quantifies the influence of strong ground motion duration (SGMD) of aftershocks on the cumulative damage caused to a RC frame structure. Understanding the effect of ground motion duration on cumulative damage and failure mechanisms will bring us one step closer to preventing future earthquake-induced collapses and can also aid in improving Building code. In order to study the effects of Duration, the other time-frequency characteristics i.e. amplitude and frequency content are kept similar. A realistic nonlinear numerical structure is modelled in SAP2000 in order to incorporate cyclic deterioration of strength and stiffness. Two sets of data are considered i.e. longer duration (>40sec) and shorter duration (<25 sec) and for each set of data cumulative damage are calculated using modified Park and Ang Damage Index. It is seen that in general longer duration data sequence causes more damage than shorter duration sequences because of longer cycles of loading

Dynamic Accumulation Damage Characteristics of Initial Cracks for the Lining of High-Speed Railway’s Tunnel

After have been analysed the initial dynamic cumulative damage mechanism of lining structure of the high speed railway tunnel,the conclusions have been gained that, under the effect of the long-term vibrating load of high speed train, When the damage energy accumulation reached a limit values, the damage zone caused by the initial crack which has been existed in the tunnel lining will be expansed further more. for the more, based on the accumulation damage theory linear elasticity and the analysis method dynamic finite element, The extension characters and calculation method of initail crack in the tunnel lining structures for the high railway have been proposed.

Insights beside assessments into small volume cyclic response of elastic plastic systems

In contrast to monotonic load studies, the engagement with a cyclic time dependent processes of small volume material response has been restrained. Crack tolerance in thin films almost by definition is restricted. Nevertheless, in terms of structural stability the fatigue resistance remains a critical concern regardless the scale. The cyclic displacement amplitudes can be enhanced by remote mechanical stress/strain or thermal origins resulted in similar outcome of cumulative irreversible micro-plasticity damage. Thus, the cyclic life in nano applications is mainly dominated by the crack nucleation controlled process. The current study is centered on the fatigue crack initiation stage as a first order design pillar and therefore require additional experimental input. Activities in elastic-plastic polycrystalline and single crystal systems in various crystal structures are described. Beside findings regarding the fatigue cracks initiation life, the role of compressive residual stress on the cyclic response has been also analyzed. The fatigue crack initiation criteria have been associated to other constitutive assessments that are related mainly to the crack stability equation elements. In addition, completely different insights are introduced into the concept of the critical film thickness, indicating the susceptibility to the crack formation. As addressed in heteroepitaxial layers, specific analogous characterization exists either in dislocation activities or by triggering crack formation. The physical aspects of threading dislocations growth and glide behavior and local decohesion ramifications are highly dependent on the layer thickness. Experimentally based, under strain control conditions at ambient temperatures the aforementioned fatigue crack initiation stage in small volume segments, obeyed a cumulative damage mechanism. It was also established that the low energy dislocation structures and the initiation life were dramatically dependent on the strain amplitude range. The role of compressive residual stress in prolonging the fatigue initiation life was also consistent. Even in silicon based materials, dislocation activities prevailed. It became apparent that categorical generalization in nano-silicon thin film fatigue behavior is beyond the susceptibility to the native oxide or environmental interaction. Issues like film processing methodology, film/substrate interfaces, residual stresses and micro-cracking feasibility occurrence as wall as critical sites still require further design insights.

Damage Assessment of Mullite Ceramic Foams in Radiant Gas Burners

The damage imposed on open-cell mullite ceramic foams was evaluated in pre-mixed radiant gas burners. After exposure to the prevailing combustion environment, foams suffered moderate strength degradation as a result of thermal stresses being imposed on the material during service. There was evidence of chemical attack during combustion although thermal shock measurements suggest that damage sustained by the foams results mainly from thermal shock rather than chemical degradation. Indeed, samples from burners subjected to ageing tests did not show additional damage compared to those subjected to short ageing tests indicating that most of damage occurred during start-up. For comparison purposes, a set of ceramic foam samples were subjected to a water quench test so that the extent to which the foams were damage by exposure to the combustion environment, under well controlled conditions, could be established. The strength retained after thermal shock by open-cell mullite foams decreased gradually with increasing quench temperatures. This suggests a cumulative damage mechanism reflecting an increase in damage throughout the material rather than sudden failure owing to propagation of pre-existing cracks along a plane. Damage in mullite foams was mainly localised at the top layer of the burners where higher temperatures and steeper thermal gradients were imposed on the material. Surprisingly, needle-like mullite crystals with a large aspect ratio were also found to have grown at the surface of the burners via a vapour feed gas-liquid catalyst-solid needle-like growth (VLS) mechanism.

Thermal Shock Behaviour of Open-Cell Cordierite Foams

Open-cell ceramic foams are being considered for a variety of applications owing to their high permeability and low weight, including molten metal filters, catalytic substrates and radiant burners. In these applications, foams are exposed to high temperatures and thermal gradients and thus the materials used require resistance to severe thermal stresses during service. Unfortunately, little is known about the thermal shock behaviour of cordierite foams when subjected to sudden changes in temperature. The objective of the present study was to investigate the thermal shock behaviour of two kinds of cordierite-based ceramic foams manufactured by the replication process. Thermal shock experiments were carried out by rapidly transferring the heated samples from a resistance furnace to a quenching bath containing distilled water followed by measuring of the retained flexural strength. Unlike dense cordierite samples that showed a sudden decrease in flexural strength at quench temperature differences above 325 K, the strength retained after thermal shock by open-cell cordierite foams decreased gradually with increasing quench temperatures. This suggests a cumulative damage mechanism reflecting an increase in damage throughout the material rather than sudden failure owing to propagation of pre-existing cracks.