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[Objectives] This paper aims to study the influence of welding defects on fatigue life of aluminum alloy plate frame.[Methods] Firstly,use X-ray to detect the welds of the test aluminum alloy plate frames with two gusset joints,and then select two plate frames with and without welding defects respectively. Then obtain main types of the welding defects through the analysis on the X-ray images. Then,carry out fatigue tests for these two plate frames with and without welding defects under different loads,so as to obtain the fatigue life of the plate frames. Finally,establish local FE models for the test plate frames with three types of welding defects by using ABAQUS software,and analyze and reveal the failure mechanism of the plate frames with welding defects.[Results] The test results show that,the failure of the test plate frame with welding defects is caused by the fracture on the longitudinal web due to the extension of the crack in the welding defect at the end of the weld;the failure of the test plate frame without welding defects,which is related to the gusset joint,is caused by the fracture on the longitudinal web due to the extension of the fatigue crack generated under the cyclic loads on the longitudinal web.[Conclusions] This study results can provide a reference for the assessment of the fatigue life and for the influence of the welding defects on the fatigue life.

With the global temperature continuing to rise, the Arctic ice is melting. The development of the Arctic route and exploitation of Arctic resources are drawing the wide attention of international society. Many countries are starting a new round of the construction of polar ships. In recent years, domestic and foreign researchers have begun to focus on the numerical study of ice loads on structure. However, the current commercial finite element software lacks a specialized element used for simulating the mechanical properties of sea ice. This lack increases the difficulty of the numerical study of ice loads on structure. In this paper, based on Reinicke and Remer's elliptic failure criteria and Winkler's elastic foundation, an element has been developed to simulate the bending failure of isotropic granular ice. The ice loads of typical marine structures, such as slope structure and conical structure, are calculated through the direct analysis method with the developed element. A comparison between the results of the direct analysis method and analytical method show good agreement. In brief, the proposed direct analysis method may provide tools and certain references for structural design in an ice environment.

The push-off angle is an important factor affecting speed-skating performance. However, quantitative evidence for the relationship between the push-off angle and foot injury is incomplete. This study aimed to establish a three-dimensional (3D) finite element model (FEM) and investigate the mechanical responses of foot structures to stress and strain to explore the relationship between injury and movement. A 3D FEM was reconstructed using CT and 3D scan data and validated by comparing the FEM-predicted and in vivo measurement data in the balanced standing state. A push-off angle obtained from a video of a champion was loaded into the FEM. The error rates of validation were less than 10%. With a decrease in the push-off angle, the stress on the metatarsal increased; the stress on the talus, ankle joint cartilage and plantar fascia decreased, as did the strain on the ankle joint cartilage and plantar fascia. The FEM was considered reasonable. Not all foot structures had an increased risk of injury with a decrease in the push-off angle from 70° to 42°. The FEM established in this study provides a possibility for further determining and quantifying the relationship between foot injury and skating technique. [ABSTRACT FROM AUTHOR]

Poverty is a social issue of global concern. Although socioeconomic indicators can easily reflect poverty status, the coarse statistical scales and poor timeliness have limited their applications. While spatial big data with reasonable timeliness, easy access, and wide coverage can overcome such limitations, the integration of high-resolution nighttime light and spatial big data for assessing relative poverty is still limited. More importantly, few studies have provided poverty assessment results at a grid scale. Therefore, this study takes the Pearl River Delta, where there is a large disparity between the rich and the poor, as an example. We integrated Luojia 1-01, points of interest, and housing prices to construct a big data poverty index (BDPI). To evaluate the performance of the BDPI, we compared this new index with the traditional multidimensional poverty index (MPI), which builds upon socioeconomic indicators. The results show that the impoverished counties identified by the BDPI are highly similar to those identified by the MPI. In addition, both the BDPI and MPI gradually decrease from the center to the fringe of the study area. These two methods indicate that impoverished counties were mainly distributed in ZhaoQing, JiangMen and HuiZhou Cities, while there were also several impoverished parts in rapidly developing cities, such as CongHua and HuaDu Counties in GuangZhou City. The difference between the two poverty assessment results suggests that the MPI can effectively reveal the poverty status in old urban areas with convenient but obsolete infrastructures, whereas the BDPI is suitable for emerging-development areas that are rapidly developing but still lagging behind. Although BDPI and MPI share similar calculation procedures, there are substantial differences in the meaning and suitability of the methodology. Therefore, in areas lacking accurate socioeconomic statistics, the BDPI can effectively replace the MPI to achieve timely and fine-scale poverty assessment. Our proposed method could provide a reliable reference for formulating targeted poverty-alleviation policies. [ABSTRACT FROM AUTHOR]

Composite double-arrow auxetic structures were designed and fabricated. The local impact experiments were carried out on the auxetic structures to explore the dynamic responses and failure modes. The effects of relative density and impulse level on the impact properties were analyzed and discussed. As the relative density increased, the local deformation of the auxetic structures and the damage of the core layer decreased, and the overall response of the auxetic structure increased. The finite element model was used to simulate the impact responses of the auxetic structures, and the numerical simulation results were in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

[Objectives] A concept named ‘component contribution rate’ is proposed to solve problems concerning the influence of ship structure components on ship structure performance.[Methods] First, a hierarchical structure is elaborated and mapped from structural components to structural performance. Second, the component contribution rate is defined in order to describe the contribution rate for a component in structural performance to fulfill its structural purpose. Next, the grey target theory is applied to quantify the component contribution rate.[Results] Finally, the application of the proposed method is demonstrated through a SWATH case study.[Conclusions] This method can be applied in the evaluation of the ship structural schemes,in order to support the optimal design of ship structure.

Due to the wave and hydrodynamic interaction between two ships advancing parallel on the ocean, their six-degrees-of-freedom motions are much more complex during replenishment. The seakeeping performance of two vessels is analyzed with AQWA. On the basis of the RAO functions of the two parallel vessels, spectrum analysis and time-domain analysis were carried out, and the significant amplitudes were obtained using the computed time-history and correlation function method. The significant amplitudes are compared with the results of the spectrum analysis and good agreement is observed. It is found that hydrodynamic interaction between two ships has a great impact on the process of replenishment. Depending on the results of the analysis, dangerous conditions during the replenishment process could be avoided, thereby ensuring the safety of supply work.

High long-term stress on the plantar fascia (PF) is the main cause of plantar fasciitis. Changes in the midsole hardness (MH) of running shoes are an important factor leading to the alteration of the PF. This study aims to establish a finite-element (FE) model of the foot–shoe, and investigates the effects of midsole hardness on PF stress and strain. The FE foot–shoe model was built in ANSYS using computed-tomography imaging data. Static structural analysis was used to simulate the moment of running push and stretch. Plantar stress and strain under different MH levels were quantitatively analyzed. A complete and valid 3D FE model was established. With an increase in MH from 10 to 50 Shore A, the overall stress and strain of the PF were decreased by approximately 1.62%, and the metatarsophalangeal (MTP) joint flexion angle was decreased by approximately 26.2%. The height of the arch descent decreased by approximately 24.7%, but the peak pressure of the outsole increased by approximately 26.6%. The established model in this study was effective. For running shoes, increasing the MH reduces the stress and strain of PF, but also imposes a higher load on the foot. [ABSTRACT FROM AUTHOR]

Deck structures subjected to drop-weight low-velocity impact are critical safety elements for ships and offshore structures. Therefore, the aim of the present study is to propose experimental research on dynamic responses of deck structures composed of stiffened plates subjected to drop-weight impact of a wedge impactor. The first step was to fabricate a conventional stiffened plate specimen and a strengthened stiffened plate specimen, as well as a drop-weight impact tower. Then, drop-weight impact tests were carried out. Test results show that local deformation and fracture occurred in the impact area. A sharp wedge impactor caused premature fracture, even under relative low impact energy; the permanent lateral deformation of the stiffened plate was reduced by 20–26% by the strengthening effect of a strengthening stiffer; residual stress and the stress concentration of the cross-joint caused by welding may cause undesired brittle fracture. The present investigation provides useful insight for improving the crashworthiness design of the deck structure of ships and offshore structures. [ABSTRACT FROM AUTHOR]

The composite re‐entrant honeycomb structures were fabricated by hot pressing and bonding processes in this article. The bending responses of composite re‐entrant honeycomb structure under three‐point bending load were studied experimentally. The bending deformation, failure process and failure load were analyzed and discussed. The influence of wall thickness gradient form which were less reported on the bending behaviors of composite re‐entrant honeycomb structures was investigated. The gradient distributions included positive gradient, negative gradient and homogeneous structures. The experimental results indicated that the wall thickness gradient design influenced the bending failure modes of composite re‐entrant honeycomb structures, and the negative gradient honeycomb structure mainly exhibited the whole bending deformation under three‐point bending loading. The influence of the relative densities on the bending behaviors of composite re‐entrant honeycomb structures was also studied. The results of three‐point bending experiment showed that the bending failure load increased significantly with the increase of relative density. [ABSTRACT FROM AUTHOR]

Due to the non-spherical perturbation of the Moon, the lifetime of ultra low-altitude Lunar spacecraft may be quite short. In this paper, we analyze the lifetime of about 50 km-altitude Lunar spacecraft with different initial orbit. The lifetime in low inclination orbits is much shorter than the ones in the near polar orbits. To extend the lifetime and keep the spacecraft in an appropriate range, an orbit maintenance strategy based on low-thrust propulsion system is proposed. The influence of the orbit initial conditions (e.g., semi-major axis, inclination, right ascension of the ascending node) on lifetime extension are discussed and the effect of the low-thrust magnitude in orbit maintenance is analyzed. According to the numerical simulation results, the lifetime of about 50 km-altitude 100 kg Lunar spacecraft with 10 kg fuel and 20 mN thruster can be extended from 7.958 days to over a 109.1725 days, which demonstrates the effectiveness of the strategy. Furthermore, a global perspective for ultra low-altitude Lunar spacecraft lifetime extension problem is provided in this paper, which can be applied to Moon mission designs extensively. [ABSTRACT FROM AUTHOR]

The effect of various heat inputs on the microstructure and impact toughness of the simulated coarse-grained heat-affected zone (CGHAS) of a niobium microalloyed (0.14 wt.%) low-carbon steel was studied. The results showed that higher impact toughness was achieved at a low heat input of 20 kJ/cm, which resulted from the formation of acicular ferrite laths/plates. They sectioned large prior austenite grains into many smaller regions, resulting in smaller crystallographic grains and high-angle grain boundaries. Conversely, when specimens were simulated with larger heat-inputs (100, 200 kJ/cm), the microstructure of the CGHAZ was predominantly composed of granular bainite plus massive MA constituents, thus impairing the impact toughness. [ABSTRACT FROM AUTHOR]

The effect of Nb-content and heat input rate on the mechanical properties and microstructure of simulated coarse-grained heat-affected zone (CGHAZ) of high-strength low-alloy steel (HSLA) was investigated. While using a low heat input (20 kJ/cm), the toughness of simulated CGHAZ was improved by increasing the Nb-content. The maximum toughness was obtained when the Nb-content was 0.110 wt.% and the heat input was 20 kJ/cm. The samples made at this condition had fine martensite/austenite (M/A-constituent), acicular ferrite and refined austenite grains. As the heat input was increased to 200 kJ/cm, the toughness of simulated CGHAZ was significantly decreased irrespective of the Nb-content because of the formation of coarse austenite grains, low angle grain boundaries, and massive M/A-constituents. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive framework for the reliability analysis of ship local structures. Existing reliability analysis of ship local structures relies on empirical analysis without experimental validation. The presented framework improves the probabilistic simulation process by combining finite element analysis and the Kriging surrogate model to increase the computational efficiency in uncertainty quantification. In addition, ultimate strength test data are introduced to update the prior distribution based on Bayesian data fusion. A cross-deck structure of a ship is studied in detail to present the application of this work. The framework provides a valuable reference for the reliability analysis of ship local structures and promotes the development of reliability-based design code. The novelty of this paper is that it introduces the combination of testing and probabilistic simulation into the reliability analysis of ship local structures. [ABSTRACT FROM AUTHOR]

Based on the design concept of functionally graded materials, the composite gradient double‐arrow auxetic structures were designed and fabricated. The thickness of core layers demonstrates an increasing trend for positive gradient structure, while a decreasing trend for negative gradient structure. The thickness of core layers keeps constant for homogeneous structure. The dynamic response and failure modes of the double‐arrow auxetic structure with different gradient distributions of wall thickness were obtained by foam projectile impact experiments. The influence of the gradient distribution of core wall thickness on the impact resistance of composite double‐arrow auxetic structures under local impact load was investigated. The results demonstrated that the gradient distribution of core wall thickness has an important influence on the dynamic response and failure modes of the structure. The negative gradient auxetic structure revealed more excellent impact resistance compared with the positive gradient auxetic structure. In addition, the response of the gradient double‐arrow auxetic structure under local impact load was simulated by ABAQUS/Explicit, and the simulation results were in good agreement with the experimental results. Combined with the experimental and numerical simulation results, it was found that the negative gradient distribution of core wall thickness had an obvious improvement on the impact resistance of composite double‐arrow auxetic structure under local impact load. [ABSTRACT FROM AUTHOR]

Engineering structures in aviation and marine experience complex loads and are often affected by repeated impact loads. The damage accumulated from deflection in the process of repeated impact will often seriously affect the safety of the structure. In this research, the low-velocity repeated impacts behavior of corrugated core structures was investigated through experimental methods. A series of low-velocity repeated impact tests were carried out to study impact resistance, taking into account the effects of varied impact sites and impact energy levels and the effects of different impact locations and different levels of impact energy. It is also observed from the test that the upper panel played a crucial role and experienced the coupling mode of the local indentations and global bending deformations during the repeated impacts tests. Three different failure modes were observed when changing the impact energies and impact locations. Moreover, the "pseudo-shakedown" phenomenon was also found when the energy of the impacts is 10 J on the short span. The present surveys provide a reliable method and insight into the dynamic response of the aluminum corrugated core structures when subjected to low-velocity repeated impacts, which could be a significant guideline for the investigation and lightweight design of shipping and aviation. [ABSTRACT FROM AUTHOR]

Similarity laws of scaled models of offshore platform deck structures under low velocity impact loading are proposed in the present research. The similarity laws of scaled models with different scaling factors are established in forms of dimensionless factors with consideration of flow stress differences of the materials. A dimensionless displacement is defined by dividing displacement by plate thickness and a dimensionless force is defined by dividing force by flow stress and plate thickness; then, a dimensionless force-displacement relationship is established. Dynamic responses of three geometrically similar stiffened structures with scaling factors of 1:4, 1:2, and 1:1 subjected to the dropping impact of a rigid triangular pyramidic impactor are investigated by an experimental test and a finite element analysis. Results show that dimensionless force-displacement curves of geometrically similar plates coincide with each other; meanwhile, the difference of maximum impact force for the three structures with various scaling factors is less than 5%, and the difference of maximum impact depth is less than 1%, which definitely show the effectiveness of the scaling laws based on dimensionless factors. The present research provides useful insight into the similarity laws of dynamic responses of deck structures subjected to falling object impact and would be used in the crashworthiness research and design process of the offshore structures. [ABSTRACT FROM AUTHOR]

The influences of elevated and cryogenic temperature on the quasi‐static indentation responses and damage mechanism for composite Y‐type cores sandwich structure were studied by experiments in present paper. The quasi‐static indentation experiments were performed to explore the indentation performances for composite Y‐type cores sandwich structures under eight different temperature conditions. The influences of the testing environment temperature on the typical indentation force‐deformation curves, damage patterns and indentation failure load were investigated and analyzed. The experimental results demonstrated that the testing environment temperature made an important influence on the deformation mechanism, typical force‐deformation curves and failure load. Fiber fracture of the front panel was found when the testing environment temperature was below the glass transition temperature, while the fiber microbuckling of the front panel was also revealed when the testing environment temperature was above the glass transition temperature. The failure load increased with the decreasing of the testing environment temperature at cryogenic temperature. Nevertheless, at elevated temperature, the failure load decreased with the increasing of the testing environment temperature attributing to the weakening of the fiber‐matrix interface performances. [ABSTRACT FROM AUTHOR]

A combined experimental study and numerical simulation is performed to investigate the effect of core materials on low-velocity impact behaviour of sandwich panels. Dynamic responses of three types of corrugated sandwich panels with the same geometric configurations, which consist of the same CFRP (carbon fibre-reinforced plastic) face sheets, but the different corrugated cores including aluminium alloy, stainless steel and CFRP are investigated in the present research. Reasonably good agreement has been achieved by comparing impact force, energy absorption and failure modes between experimental results and numerical simulation predictions. The present research reveals that fracture stress and fracture strain of the core material have a significant influence on the performances of the sandwich panels under low-velocity local impact, sandwich panels with stainless steel core has the largest capability of load carrying and energy absorption. Conclusions presented in the present research would be used in the development of neoteric lightweight multifunctional smart structures. [ABSTRACT FROM AUTHOR]

This paper addresses a simplified analytical method for evaluating the impact responses of the stiffeners in a ship side shell subjected to head-on collision by a bulbous bow. The stiffeners are classified as the "central stiffener" and the "lateral stiffener" according to their relative position to the bulbous bow. In analytical predictions, it is assumed that the flexural bending of the central stiffener and plate occurs simultaneously. However, the deformation mode of the central stiffener outside the indenter contact region is simplified as linear to derive its deformation resistance. The curved deformation mode of the lateral stiffener is proposed to calculate the deformation resistance and to consider the interaction effect with the plate, which can cause the plate to fracture earlier. Model tests with three specimens (one unstiffened plate for reference and two stiffened plates) quasistatically punched by a conical indenter are performed to validate the proposed analytical method. Resistance-penetration curves and damage shapes for the three specimens are obtained. The experimental results illustrate the effects of the stiffeners on the deformation resistance and fracture initiation of the stiffened plate and the influence of stiffener tripping on the lateral resistance. Moreover, the experimental and analytical predicted results correspond well, suggesting that the proposed analytical method can accurately predict the crashworthiness of a ship side shell subjected to bulbous bow collision. [ABSTRACT FROM AUTHOR]

Experimental investigations on the mechanical responses of fully clamped circular plates with prefabricated crack at room temperature and low temperature have been conducted. Initial cracks with different lengths were prefabricated by the electrical discharge machining method. Low ambient temperature was created by the liquid nitrogen in a low-temperature chamber, and a dropping hammer was dropped from the same height with a constant impact energy of 5 J to carry out the repeated impact. Experimental test results show that the prefabricated crack has a significant influence on the mechanical behavior of the thin plates. The maximum impact force decreases with increase of the crack length, and the threshold impact number until fracture decreases with increase of the crack length. It is also observed from the test results that the maximum impact force increases with decrease of the temperature, while threshold impact number until fracture and the plastic permanent deformation decreases due to the brittleness of the material in low temperature. The present investigations provide useful insight into the failure mechanism of the clamped thin plate with initial crack under low-velocity repeated impacts in low temperature, which will lead to a guideline for research and design of marine structures in the arctic area. [ABSTRACT FROM AUTHOR]

This paper investigates the behaviour of aluminium alloy plates with and without initial cracks under repeated impacts. Three series of impact tests were conducted to study the behaviour of circular plate that do not have any cracks (series B), have surface cracks with varying length (series L), and have cracks varying depths (series D). A hammer was dropped from the same height with a constant initial striking energy 60J for all tests. It was observed that plates with larger cracks carried smaller impact forces and assumed larger deformations. With the increase in impact number, the effects of crack lengths and depths on the dynamic behaviour became much more significant. Predictions using a rigid-plastic theoretical model were compared with these test results. With the stresses determined based on the true strain-stress curve obtained by standard tension test, the refined analytical formula provides better predictions that agree well with the lab tests. [ABSTRACT FROM AUTHOR]

[Objectives] This paper aims to study the effects of initial cracks on the dynamic response of aluminum alloy plate under repeated impacts.[Methods] Through the repeated impact test and finite element simulation of the aluminum alloy plate, we analyze the dynamic response characteristics of the aluminum alloy plate under repeated impacts, and compare the impact loads and failure modes of the aluminum alloy plate with and without initial cracks.[Results] The test results are in good agreement with the simulation calculations. The results show that the aluminum alloy plate is sensitive to initial cracks under repeated impacts;the initial cracks can reduce the load carrying capacity of the aluminum alloy plate,resulting in the reduced impact load and the reduced number of the repeated impacts for failure; the failure modes are also influenced by the initial cracks under repeated impacts.[Conclusions] The research in this paper provides a certain basis and reference for calculating and evaluating the structure strength of aluminum alloy hull plate.