Analysis of biaxial proportional low-cycle fatigue crack propagation for hull inclined-crack plate based on accumulative plasticity

Fracture failures of ship plates subjected to in-plane biaxial low-cycle fatigue loading are generally the coupling result of accumulative plasticity and biaxial low-cycle fatigue damage. A biaxial low-cycle fatigue crack growth analysis of hull structure that accounts for the accumulative plasticity effect can be more suitable for the actual evaluation of the overall fracture performance of the hull structure in severe sea conditions. An analytical model of biaxial low-cycle fatigue crack propagation with a control parameter for ∆CTOD is presented for hull inclined-crack plate. A test was conducted for cruciform specimens made of Q235 steel with an inclined crack to validate the presented analysis. The biaxial accumulative plasticity behavior and the effects of biaxiality and stress ratios were investigated. The results of this study reveal a strong dependence of biaxial low-cycle fatigue crack propagation on biaxial accumulated plasticity.

Bearing Capacity Analysis of Transmission Tower Structure Considering Corrosion Damage

As an important part of power grid equipment, transmission towers are in direct contact with the external environment for a long time. As a coastal city in China, Fujian has been affected by marine environment and industrial pollution for a long time, which directly affects the safety of transmission towers in long-term service. In order to explore the changes of the ultimate bearing capacity of the tower structure after corrosion, this paper uses finite element software to analyse the mechanical properties of the tower structure during long-term service, and finds that the 45° wind direction is the control condition, and the overall stiffness of the tower decreases with the growth of corrosion time, and the increment of tower top displacement reaches 7% at 12 years of corrosion. The corrosion-sensitive members of the tower were clearly identified, and their stress ratios increased from 0.78, 0.79, and 0.83 to 0.97, 0.98, and 0.99, respectively, at 12 years of corrosion.

Production of English lexical stress by Mandarin speakers: Acoustics and kinematics

This study aims to understand if Mandarin late learners of English can successfully manipulate acoustic and kinematic cues to deliver English stress contrast in production. Mandarin ( N = 8) and English ( N = 8) speakers were recorded producing English trochaic (initial stress) and iambic (final stress) items during a nonword repetition task. Speakers’ jaw movement for the utterances was tracked and analysed. Acoustic and kinematic cues were measured for each syllable, including acoustic duration, fundamental frequency (F0), and intensity, as well as jaw movement duration, displacement, peak velocity, and stiffness. Stress ratios (syllable 1 / syllable 2) were calculated for each cue and compared between groups. Results showed that English and Mandarin speakers had generally comparable performance in differentiating trochaic from iambic patterns, as well as in the degree of between-syllable contrast within each pattern. Between-group differences were only observed in acoustic duration and jaw movement velocity/stiffness. These results suggest that the experience with Mandarin stress contributes to Mandarin speakers’ overall successful production of English stress but also results in nonnative use of some acoustic/kinematic cues.

Development of a Vibration Technique Based on Geometric Optimization for Fatigue Life Evaluation of Sandwich Composite Structures

A major obstacle to obtaining cost-effective experimental data on the fatigue life of sandwich panels is the prohibitive amount of time and cost required to carry out millions of cycles. On the other hand, vibration techniques applied to sandwich geometries fail to match the stress patterns that are obtained from standard flexural fatigue tests. To overcome such limitations, a vibration-based fatigue technique is proposed, which entails the use of sandwich specimens whose geometries are optimized to reproduce the stress distribution observed during three point bend loading while vibrating at the first resonant frequency. The proposed vibration technique was experimentally validated. The results, compared with the average number of cycles to failure at different stress ratios obtained via the Three-Point Bending test, showed high levels of accuracy. The proposed method is robust and time effective and indicates the possibility of attaining fatigue lifetime prediction of a wide class of composite elements, such as sandwich panels.

Small strain stiffness for granite residual soil: effect of stress ratio

Most previous studies have focused on the small strain stiffness of sedimentary soil while little attention has been given to residual soils with different properties. Most studies also neglected the effects of the deviator stress, which is extensively involved in civil engineering. This note considers the effects of the deviator stress on the small-strain stiffness of natural granite residual soil (GRS) as established from resonant column tests performed under various stress ratios. Although increasing the stress ratio results in a greater maximum shear modulus for both natural and remolded residual soils, remolded soil is more sensitive to changes in the stress ratio, which highlights the effects of soil cementation. The data herein offers new insights to understand the stiffness of residual soil and other weathered geomaterials.

An experimental approach on calcarenite reservoir dilation factor

The time of flight of a plane wavefront generated from an acoustic pulse is expected to decrease when the medium length between the wave emitter and receiver is shortened. This simple idea is extrapolated to the case of reservoir compaction in order to obtain a geophysical parameter R (dilation factor) that relates the rock deformation to the variation of time of flight (also called time-lapse time shift in 4D seismics) or acoustic velocity of a plane wave propagating in the same direction of deformation. Interpretation of a few laboratory compressive tests with simultaneous ultrasonic acquisition, performed on oil-saturated calcarenite samples, are presented and discussed. The samples were subjected to several stress regimes and simultaneous ultrasonic acquisitions. Despite the formerly ultrasonic acquisition rate limitations, it was possible to obtain R values for various lateral-vertical stress ratios for each sample's linear and nonlinear stress-strain trends.

Set-up of a Generalized Dataset for Crack-Closure-Mechanisms of Cast Steel

In components, crack propagation is subjected to crack-closure-mechanisms which affect the build-up of the relevant threshold stress intensity factor range during cyclic loading. As structural parts are exposed to service loads incorporating a variety of load ratios, a significant change of the long-crack threshold value occurs, leading to a severe stress ratio dependency of crack-closure-mechanisms. Thus, an extensive number of crack propagation experiments is required to gain statistically proven fracture mechanical parameters describing the build-up of closure effects as crack growth resistance curves.The article presents a generalized dataset to assess the formation of crack-closure-mechanisms of cast steel G21Mn5+N. Numerous crack propagation experiments utilizing single edge notched bending (SENB) sample geometries are conducted, incorporating alternate to tumescent stress ratios. The statistically derived, generalized crack growth resistance curve features the impact of closure effects on the crack propagation rate in a uniform manner. To extend the dataset to arbitrary load ratios, the long-crack threshold approach according to Newman is invoked. The generalized dataset for the cast steel G21Mn5+N is validated by analytical fracture mechanical calculations for the utilized SENB-sample geometries. Incorporating a modified NASGRO equation, a sound correlation of analytical and experimental crack propagation rates is observed. Moreover, the derived master crack propagation resistance curve is implemented as a user-defined script into a numerical crack growth calculation tool and supports a local, node--based numerical crack propagation study as demonstrated for a representative SENB-sample. Concluding, the derived dataset facilitates the calculation of fatigue life of crack-affected cast steel components subjected to arbitrary stress ratios.

Tension-Compression Fatigue Induced Stress Concentrations in Woven Composite Laminate

Tension-compression (T-C) fatigue response is one of the important design criteria for carbon-fibre-reinforced polymer (CFRP) material, as well as stress concentration. Hence, the objective of the current study is to investigate and quantify the stress concentration in CFRP dog-bone specimens due to T-C quasi-static and fatigue loadings (with anti-buckling fixtures). Dog-bone specimens with a [(0/90),(45/−45)4]s layup were fabricated using woven CFRP prepregs and their low-cycle fatigue behaviour was studied at two stress ratios (−0.1 & −0.5) and two frequencies (3 Hz & 5 Hz). During testing, strain gauges were mounted at the centre and edge regions of the dog-bone specimens to obtain accurate, real-time strain measurements. The corresponding stresses were calculated using Young’s moduli. The stress concentration at the specimen edges, due to quasi-static tension, was significant compared to quasi-static compression loads. Furthermore, the stress concentration increased with the quasi-static loading within the elastic limit. Similarly, the stress concentration at the specimen edges, due to tensile fatigue loads, was more significant and consistent than due to compressive fatigue loads. Finally, the effects of the stress ratio and loading frequency on the stress concentration were noted to be negligible.

Stress anisotropy in natural debris flows during impacting a monitoring structure

The frictional resistance of rock and debris is supposed to induce stress anisotropy in the unsteady, non-uniform flow of gravitational mass flows, including debris flows. Though widely used in analytical models and numerical simulation tools, concurrent measurements of stresses in different directions are not yet available for natural flow events. The present study aims to investigate the relation of longitudinal and bed-normal stress exerted by two natural debris flows impacting a monitoring barrier in the Gadria creek, Italy. For that, a force plate in front of a barrier was used to continuously record forces normal to the channel bed, whereas load cells mounted on the vertical wall of the barrier recorded forces in flow direction. We observed an anisotropic stress state during most of the flow events, with stress ratios ranging between 0.1 and 3.5. Video recordings reveal complex deposition and re-mobilization patterns in front of the barrier during surges and highlight the unsteady nature of debris flows. These first-time in-situ measurements confirm the assumption of stress anisotropy in natural debris flows for gravitational mass flows, and provide data for model testing.