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The properties of energy absorption can be effectively improved by different induced structures for thin-walled straight tube.Finite element software（LS-DYNA） was used to simulate the transient response of thin-walled circular tube with internal and outer staggered grooves under axial impact.Axial shock characteristics of force for thin-walled circular tubes with different grooves were compared.The mean load formula considering strain rate effect was derived based on Hosseinipour ’s deformation model.Geometric parameter was introduced to predict peak load.The results show that the thin-walled circular tube with internal and outer staggered grooves can reduce 62.24% peak load and 56.26% mean load compared with thin-walled straight tube.The fold deformation is symmetrical and consistent with Hosseinipour’s deformation model.The prediction results of mean load and peak load are consistent with the finite element results.

The objective of this research paper is to propose a general methodology for the design of a foam filled tube which is lighter and more efficient in terms of Specific Energy Absorption (SEA) and Crush Force Efficiency (CFE) than an existing square aluminium empty tube for energy absorption application. The analytical expressions are used to determine the mean load during Quasi-Static axial compression loading of the foam filled tubes. The fact the thinner tubes develop lower peak load and the higher plateau stress of the foam results in higher mean load are used in the analytical calculations. Hence, the tube thickness and the foam density are chosen as the variables. The analytical results are compared with the experimental results of the initial design to choose the best design. An FE model is used as a tool to verify and predict the characteristics of the proposed design. Finally, the experimental model of the proposed design is built and its crushing behaviour is compared against the initial design. The foam used to fill the tube is high density Polyurethane (PU) foam. The experimental validation of intermediate designs is eliminated. Thus, the time of overall design cycle is reduced.

The paper presents results of calculation for modelling of the stressstrain relationship in the case of block loads with mean load value. A model, based on the stable hysteresis loops, was assumed and modified to use for block loading analysis. For stress history calculation, the proposed model and two other constitutive models were used. Results of fatigue test of specimens made of S355J0 steel subjected to bending block loading with mean load value are presented and used to verify the proposed model. In the tests, the mean load was increased and decreased in subsequent blocks. The changes of strain recorded during the tests shown in the paper indicate a different behavior of the material. Damage accumulation degree for block sequence was used to compare the results of calculations. It was shown, that stress history parameters (stress amplitude and mean stress value in this case) are similar for all investigated models

The literature in the area of material fatigue indicates that the fatigue properties may change with the number of cycles. Researchers recommend taking this into account in fatigue life calculation algorithms. The results of simulation research presented in this paper relate to an algorithm for estimating the fatigue life of specimens subjected to block loading with a nonzero mean value. The problem of block loads using a novel calculation model is presented in this paper. The model takes into account the change in stress–strain curve parameters caused by mean strain. Simulation tests were performed for generated triangular waveforms of strains, where load blocks with changed mean strain values were applied. During the analysis, the degree of fatigue damage was compared. The results of calculations obtained for standard values of stress–strain parameters (for symmetric loads) and those determined, taking into account changes in the curve parameters, are compared and presented in this paper. It is shown that by neglecting the effect of the mean strain value on the K′ and n′ parameters and by considering only the parameters of the cyclic deformation curve for εm = 0 (symmetric loads), the ratio of the total degree of fatigue damage varies from 10% for εa = 0.2% to 3.5% for εa = 0.6%. The largest differences in the calculation for ratios of the partial degrees of fatigue damage were observed in relation to the reference case for the sequence of block n3, where εm = 0.4%. The simulation results show that higher mean strains change the properties of the material, and in such cases, it is necessary to take into account the influence of the mean value on the material response under block loads.

Highlights • Mechanism of microstructure in different thickness positions of TRTs are discussed. • Crashing tests and simulation of TRTs are performed and compared. • Novel theoretical model of TRTs with axially varying thickness and material strengths are established. • Effects of the thickness and material strengths on the heights of folding elements are analyzed. • Different tube structures are selected to compare the crashing behaviors by adopting novel model. Abstract By adopting the variable gauge rolling (VGR) technology and the annealing process, the tailor rolled blanks (TRBs) with both continuously varying thickness and inhomogeneous material properties could be obtained. Through the procedure of subsequent forming and laser welding technology on TRBs, the tailor rolled tubes (TRTs) with axially varying thickness and material properties were successfully produced, and performed by the quasi-static axial crushing afterwards. On the basis of the microstructural transformation at different thickness locations, the relationships between the material properties and thicknesses were analyzed. Moreover, the failure mode and the deformation mechanism of TRTs have been discussed. It is noted that the progressively increased distances between the top and bottom of the plastic hinges is the essential characteristic. Combined with the classical crushing theories and models, a novel predictive mathematical model considering the thickness variation, changing material properties and variety heights of folding elements has been established. Compared with the series conventional computing models, this novel model performed better. On this foundation, the effects of different thickness transition form and distribution of material properties on the crushing performances were investigated. Besides, detailed effects of the tube structure and with or without changing material properties on the crushing capacity were also studied by introducing the concept of equivalent strength and equivalent thickness. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

Results from full scale fatigue tests of offshore mooring chains are analyzed. The data set includes new and used chains, tested at a variety of mean load levels. The used chains have been retrieved after operation offshore and include samples with varying surface conditions, ranging from as-new to heavily corroded. Based on a parameterized S–N curve intercept parameter, the effects of mean load and chain condition are estimated empirically by regression analysis. A hierarchical linear model is used, to account for and quantify correlations within subsets of the data. The choice of grouping criterion for the hierarchical model is discussed, and assessed based on the current data. Results show that the mean load and corrosion effects are both significant. Differences in the fatigue performance of new versus used chains are quantified and discussed. • S–N data at a range of mean loads for new and used, corroded chain is analyzed. • Hierarchical linear model accounts for correlation within groups of chain. • Grouping criterion for data set considered is discussed and assessed based on data. • Parameters of a mean load and corrosion dependent S–N intercept are estimated. • Effects of mean load and corrosion are found to be significant. [ABSTRACT FROM AUTHOR]

The paper presents results of calculation for modelling of the stressstrain relationship in the case of block loads with mean load value. A model, based on the stable hysteresis loops, was assumed and modified to use for block loading analysis. For stress history calculation, the proposed model and two other constitutive models were used. Results of fatigue test of specimens made of S355J0 steel subjected to bending block loading with mean load value are presented and used to verify the proposed model. In the tests, the mean load was increased and decreased in subsequent blocks. The changes of strain recorded during the tests shown in the paper indicate a different behavior of the material. Damage accumulation degree for block sequence was used to compare the results of calculations. It was shown, that stress history parameters (stress amplitude and mean stress value in this case) are similar for all investigated models. [ABSTRACT FROM AUTHOR]

A reliability formulation for mooring chain fatigue is developed, including the effects of mean load and degradation due to corrosion. They are included by starting from a S-N model with parameterized dependence to the mean load and a customized corrosion condition scale. The paper includes a thorough case study, based on a realistic case. A global sensitivity analysis is used to justify a reduction of the model dimension. A reliability analysis is then performed, and the effect on failure probability from variation of a range of parameters and model assumptions is studied. • Reliability formulation for fatigue of mooring chain segment. • Formulation accounts properly for mean load and corrosion effects. • Global sensitivity analysis is used to reduce the model dimension. • Thorough case study demonstrates impact of relevant parameters and properties. [ABSTRACT FROM AUTHOR]

The acute physiological processes during “aerobic” high-intensity interval exercise (HIIE) and their regulation are inadequately studied. The main goal of this study was to investigate the acute metabolic and cardiorespiratory response to long and short HIIE compared to continuous exercise (CE) as well as its regulation and predictability. Six healthy well-trained sport students (5 males, 1 female; age: 25.7 ± 3.1 years; height: 1.80 ± 0.04 m; weight: 76.7 ± 6.4 kg; VO2max: 4.33 ± 0.7 l•min-1) performed a maximal incremental exercise test (IET) and subsequently three different exercise sessions matched for mean load (Pmean) and exercise duration (28 min): 1) long HIIE with submaximal peak workloads (Ppeak = power output at 95 % of maximum heart rate), peak workload durations (tpeak) of 4 min, and recovery durations (trec) of 3 min, 2) short HIIE with Ppeak according to the maximum power output (Pmax) from IET, tpeak of 20 s, and individually calculated trec (26.7 ± 13.4 s), and 3) CE with a target workload (Ptarget) equating to Pmean of HIIE. In short HIIE, mean lactate (Lamean) (5.22 ± 1.41 mmol•l-1), peak La (7.14 ± 2.48 mmol•l-1), and peak heart rate (HRpeak) (181.00 ± 6.66 b•min-1) were significantly lower compared to long HIIE (Lamean: 9.83 ± 2.78 mmol•l-1; Lapeak: 12.37 ± 4.17 mmol•l-1, HRpeak: 187.67 ± 5.72 b•min-1). No significant differences in any parameters were found between short HIIE and CE despite considerably higher peak workloads in short HIIE. The acute metabolic and peak cardiorespiratory demand during “aerobic” short HIIE was significantly lower compared to long HIIE and regulable via Pmean. Consequently, short HIIE allows a consciously aimed triggering of specific and desired or required acute physiological responses. [ABSTRACT FROM AUTHOR]

It has been widely known for some time that the mean stress affects the fatigue strength of steel. This is distinctly evident when working with non-welded or stress-relieved welded details. Some consequences of this influence are revealed when evaluating the stress history, or when counting the cycles.In this paper, decisive influences on the plain fatigue limits or strengths are indicated, when applying a mean stress, together with the effects of both combined stress and anisotropy and the minimum stress required to grow a crack of a given length and depth.

The literature in the area of material fatigue indicates that the fatigue properties may change with the number of cycles. Researchers recommend taking this into account in fatigue life calculation algorithms. The results of simulation research presented in this paper relate to an algorithm for estimating the fatigue life of specimens subjected to block loading with a nonzero mean value. The problem of block loads using a novel calculation model is presented in this paper. The model takes into account the change in stress–strain curve parameters caused by mean strain. Simulation tests were performed for generated triangular waveforms of strains, where load blocks with changed mean strain values were applied. During the analysis, the degree of fatigue damage was compared. The results of calculations obtained for standard values of stress–strain parameters (for symmetric loads) and those determined, taking into account changes in the curve parameters, are compared and presented in this paper. It is shown that by neglecting the effect of the mean strain value on the K′ and n′ parameters and by considering only the parameters of the cyclic deformation curve for εm = 0 (symmetric loads), the ratio of the total degree of fatigue damage varies from 10% for εa = 0.2% to 3.5% for εa = 0.6%. The largest differences in the calculation for ratios of the partial degrees of fatigue damage were observed in relation to the reference case for the sequence of block n3, where εm = 0.4%. The simulation results show that higher mean strains change the properties of the material, and in such cases, it is necessary to take into account the influence of the mean value on the material response under block loads. [ABSTRACT FROM AUTHOR]