Effects Of Load Duration Research Articles

The in-situ testing and modeling on sealing strength deterioration of lithium-ion pouch cell

The pouch cell is of great potential application among a variety of power batteries, because of its higher energy density and lower weight. Due to the existence of internal gas generation in the long lifetime of the pouch cell, the slowly increasing internal gas pressure will cause a time-dependent fracture in its package sealing edge. This process significantly affects the remaining useful life and reliability. In this paper, an in-situ experiment was performed and a modified cohesive zone model (CZM) was proposed to describe the seal strength degradation behavior. Firstly, the in-situ tensile test was conducted to measure the sealing strength curve, and the exponential CZM was used to characterize the constitutive relation of the sealing area based on the load-displacement data. Secondly, constant stress accelerated degradation tests (CSADT) were carried out to simulate the degradation process, where the action of gas pressure on sealing area was converted to accelerated tensile load. Then, the exponential CZM was modified to account for the strength degradation behavior with the effect of constant load duration, based on the traction-separation relationship. The fracture energy was calculated by area integral under the load-displacement curve, whose reduction represented the degradation phenomenon. Finally, the proposed model was validated by the testing data, and a good agreement was observed.

Dynamic Buckling of Cylindrical Composite Panels Under Axial Compressions and Lateral External Pressures

In this paper, dynamic buckling analysis of composite cylindrical panels under two separately suddenly applied loads (axial compression and lateral external pressure) is investigated. Abaqus/Explicit operator has been used to monitor time responses of the structure under various magnitudes of loads in order to determine the critical dynamic buckling loads based on the Budiansky–Roth criterion. The effect of boundary conditions and loading duration is studied thoroughly in this work.

Calibrating wood products for load duration and rate: a statistical look at three damage models

Lumber and wood-based products are versatile construction materials that are susceptible to weakening as a result of applied stresses. To assess the effects of load duration and rate, experiments have been carried out by applying preset load profiles to sample specimens. This paper studies these effects via a damage modeling approach, by considering three models in the literature: the Gerhards and Foschi accumulated damage models, and a degradation model based on the gamma process. A statistical framework is presented for fitting these models to failure time data generated by a combination of ramp and constant load settings, and it is shown how estimation uncertainty can be quantified. The models and methods are illustrated and compared via a novel analysis of a Hemlock lumber dataset. Practical usage of the fitted damage models is demonstrated with an application to long-term reliability prediction under stochastic future loadings.

Biodynamic timber sheet pile walls: vegetation retaining structure

Timber sheet pile walls are widely used for the protection of stream banks in different parts of the world. However, there is a tendency to create more sustainable types of stream banks not only because exploitable wood is more difficult to obtain, but also because of disturbance to the natural habitat of plants and animals due to hard embankments. In the Netherlands alone, about 2500 km of engineered timber sheet pile wall embankments exist, primarily made with tropical hardwood, besides an even much larger amount of ‘non-engineered’ small-size timber-based embankments. As an alternative, the authors propose to use a mixed timber sheet pile-vegetation system, where locally available timber can be applied in combination with natural vegetation. Unlike the usual bioengineering scheme, vegetation is not seen as an element, which could replace the timber sheet piles. Instead, a new perspective is tested, where the vegetation is included as a ‘structural’ element which can even counteract the consequences of time-dependent biological degradation of the timber sheet pile. By doing so, both long-term durability as well as reliability of the stream bank is improved. A comprehensive design strategy was developed based on well-established sub-models from the literature on plant growth, root reinforcement as well as timber damage accumulation. The timber sheet pile wall-vegetation system is illustrated in an example case study. Preliminary analysis including only the mechanical reinforcement of vegetation shows that there is a decrease in moment and shear acting on the timber sheet pile with growth of the vegetation. Consequently, the damage accumulation due to load duration effects on the timber decreases and the service life of the system increases. Thus, using vegetation in combination with highly degradable timber could possibly negate the need for using hardwood timber, or more generally, save resources that are currently used for these structures.

Research on Meshing Characteristics of Shearer Walking Wheel Based on Rigid-Flexible Coupling

Frequent failure of the walking wheel seriously restricts the performance of the whole shearer. To reduce the failure rate and improve the working performance of the walking wheel, the meshing characteristics of the tooth pin are researched. The dynamic state equations of the walking wheel and the contact force model of tooth pin meshing are established. The rigid-flexible coupling simulation model of tooth pin meshing is built. The load distribution characteristics of the walking wheel are analyzed, as well as the effects of impact load amplitude and duration. Results show that the curve of the longitudinal load distribution coefficient (Kβ) of the contact area is W-shaped, with a maximum of 1.325 at the moment of a single tooth contact. The end of the transition curve is the most serious position of the longitudinal load imbalance at the tooth root. In addition, on the impact moment,Kβtends to decrease and maximum stress obviously increases with the increase in impact load under 40%; the material at the contact position will fail under an extra 39% instantaneous impact load. Furthermore, with the impact load of 30%, the influence of load impact duration under 0.5 s on the meshing characteristics of the walking wheel is relatively faint. The results provide some guidance for the design optimization of the walking wheel and provide a reference for improving the reliability of the shearer.

Effects of Load Duration and Stress Level on Deformation and Particle Breakage of Carbonate Sands

Abstract Time-dependent deformation of crushable soils attributable to particle breakage could dominate the postconstruction stability of high rockfill dams and pile foundations. The evolutionary t...

Dynamics behavior and imperfection sensitivity of a fluid-filled multilayered FGM cylindrical structure

The paper aims to investigate the transient response of an air-filled multilayer hollow functionally graded (FGM) cylinder with interlaminar bonding imperfection in the presence of load which is extensively put to use in aerospace structure. The material properties of each layer are assumed to vary continuously within the cylinder along the thickness direction with arbitrary grading pattern. A linear spring model is used to define imperfectly bonded interfaces of the multilayer cylinder. The solution of problem is obtained by means of the laminate approximation theory along with the Durbin's numerical Laplace transform inversion with regard to the time coordinate. Detailed numerical study of transient response of multilayer FGM cylinder with imperfect bonding under a pulse excitation are presented. In the following, the effect of imperfection on radial and circumferential stresses is presented and in view of the lack of any data, only the obtained results with the perfect bond are compared to those of other researchers have published in the literature. Also, by displaying contours of the internal pressure field, dynamic features in the fluid-structure interaction are investigated. Finally the effect of load duration and various loads, including step load and exponential load on radial and circumferential stresses are examined in detailed and the results obtained show the effect of step load is more critical than exponential load.

Association of maternal HIV-1 severity with dental caries: an observational study of uninfected 5- to 7-yr-old children of HIV-1-infected mothers without severe immune suppression.

Treatment programs to prevent perinatal and postnatal HIV-1 transmission have become available in sub-Saharan Africa, leading to an emerging population of HIV-1 exposed uninfected (HEU) children. Exposure to HIV-1 in utero and during breastfeeding may increase the risk of morbidity and mortality in HEU children. This study estimated the association of the severity of maternal HIV-1 infection as assessed by CD4 count and viral load at baseline (7d postpartum), with dmft count of their 5- to 7-yr-old HEU offspring. A follow-up study was conducted of HIV-1-infected mother-HEU children pairs (n=164) from the Ugandan site of the ANRS 12341-PROMISE- PEP trial (ClinicalTrials.gov, number NCT00640263). HIV-1-infected mothers were interviewed and the HEU children were examined for caries using the World Health Organization's survey methods for field conditionsand the dmft index. Directed acyclic graphs and negative binomial regression were used for analyses. The prevalence of 1 or more dmft was 48%. Negative binomial regression showed no association between the dmft count and maternal CD4 counts 7d postpartum but a 10% lower dmft count with longer breastfeeding duration was found. Maternal CD4 count at birth was not associated with the dental caries experience in uninfected children born to women without severe immune suppression, while there appeared to be a protective effect of high viral load and breastfeeding duration.

Critical THI thresholds based on the physiological parameters of lactating dairy cows.

The severity of heat stress conditions in high-yielding dairy cows is currently underestimated. The present study aimed to determine the heat load threshold of the temperature-humidity index (THI) on physiological parameters of lactating Holstein-Friesian cows under a continental climatic zone in Germany. Physiological parameter measurements, such as respiration rate (RR), measured hourly, and heart rate (HR) and rectal temperature (RT), both measured twice daily, were performed in a total of 139 multiparous cows on three randomly chosen measurement days per week. In addition, the ambient temperature and relative humidity of the barn were recorded every 5min to calculate the current THI. The physiological parameter data were linked to the THI, and the heat load thresholds were determined using the broken-stick model. The heat load duration effect of each physiological parameter was obtained by regression analysis. Considering the increases in the physiological parameters, our study provided reliable data to determine heat load thresholds for lactating high-yielding dairy cows in a moderate climatic zone. The heat load threshold could be determined for RR in standing cows (THI=70) and lying cows (THI=65) and for HR (THI=72) and RT (THI=70) in standing cows. The heat load duration also demonstrated a significant effect on the increases in physiological parameters among dairy cows. In particular, the present study enabled a strategy to be devised to initiate heat mitigation in high-yielding dairy cows when they are exposed to THIs above 65.

Duration of load behaviour of a glued shear plate dowel joint

An experimental study on the duration of load effects in a glued shear plate dowel joint was conducted. The joint design features a single large diameter dowel for load transfers between members, via external steel plates, which are bonded to the timber with a low stiffness bond line. Due to the low bond line stiffness, the timber element is subjected to a close to uniform shear stress distribution over the bond area. The study comprises a total of 80 test specimens loaded in shear, both parallel and perpendicular to the grain, at three load levels in the range of 50–80% of the short-term failure load. All specimens failed within approximately 110 days in outdoor sheltered conditions during which time deformations were recorded for one specimen of each type and load level. The study found a significantly larger influence of duration of load for this dominant shear action than what is reported in the literature for bending tests. The method of ranked stress was used to determine a suggested reduction factor kmod for the shear plate dowel joint to 0.10 and 0.30 for parallel and perpendicular loading, respectively. This is a rough estimate based upon a 50-year extrapolation of 4-month data. Thus, it must be concluded that the studied shear plate dowel joint is not efficient in terms of long-duration loads in outdoor sheltered climate, and that further studies are needed in order to verify the use in other climates. It is also evident in this study that there is a lack of knowledge and empirical evidence on the duration of load effects in timber for shear loading.

The effect of loading duration on damage initiation in high-strength concrete

The rate sensitivity of the failure strength of concrete and other brittle materials is well documented. However, the underlying mechanism(s) that gives rise to this phenomenon remains a topic of debate. Experimental results suggest that the time-dependent failure process plays a significant role in the observed strength increase. This study investigates the failure process in high-strength concrete (HSC) specimens under uniaxial compression loading. This is accomplished through the use of a modified Kolsky compression bar to apply controlled and repeatable mechanical loading in combination with the non-destructive observation capability of high-resolution X-ray computed-microtomography (micro-CT). The evolution of specimen damage morphology is observed as a result of intermittent short-duration uniaxial stress loadings. Experimental results show that HSC specimens are capable of supporting the applied stress above their quasi-static failure strength for short durations. This duration is found to be a function of the overload stress level. Additionally, micro-CT results reveal that specimens undergo a brief period of void compaction followed by the coalescence and propagation of cracks before completely losing load bearing capability.

Design and operation verification of an automated pressure mapping and modulating seat cushion for pressure ulcer prevention

A sensorized air cell-based seat cushion system was developed to address the issues of loading magnitude and duration at a sitting interface to aid in reducing risk of sitting acquired pressure ulcers. This system is capable of pressure mapping, redistribution, and offloading which were verified using an anthropomorphic model and a human subject. The system is comprised of an air cell array cushion, a pneumatic control unit, and a graphical user interface. ISO load deflection testing confirmed that the cushion's loading response is comparable to commercial air cell-based seat cushions. Testing demonstrated that the internal pressure of the air cells are indicative of interface pressure and can be used as input to pressure modulating algorithms. Uniform pressure distribution was achieved through automated pressure redistribution algorithm implementation where the immersion of a subject into the seat cushion increased and interface pressure decreased. High pressure point identification and automatic offloading were performed in which newly created high pressure points were addressed using subsequent redistribution. Pressure mapping enabled offloading and redistribution can objectively manage the effects of loading magnitude and duration at the sitting interface.

The Duration of Load Effect in Lumber as Stochastic Degradation

This paper proposes a Bayesian framework for applying a gamma process model for reliability analysis in structural engineering under time–varying stochastic loads. We focus on an important application to engineered wood products and thereby demonstrate how the proposed methodology can be implemented in practice. We use a gamma process to characterize the degradation over time in each piece of lumber, allowing for variability between pieces when external forces from loads are applied to a population of lumber. We propose a model for the shape parameter to accommodate time–varying loads. Our approach is compared with traditional accumulated damage models. Our statistical analysis of experimental data highlight the limitations of using accelerated testing to assess long–term reliability, as seen in the wide posterior intervals. This suggests the need for more comprehensive testing in future applications, or to encode appropriate expert knowledge in the priors used for Bayesian analysis.

Reliability of laminated veneer lumber (LVL) beams manufactured from early to mid-rotation subtropical hardwood plantation logs

This paper presents the reliability analysis of Laminated Veneer Lumber (LVL) beams manufactured from veneers recovered from early to mid-rotation (juvenile) subtropical hardwood plantation logs, with plantations established either for sawn timber applications or pulpwood production. While these logs have a high number of natural defects (knots, gum veins, grain deviation, etc.), are considered of low quality and have little to no commercial value, they produce high strength Veneered Based Composite products, such as Plywood and LVL. Yet, the reliability of these products is unknown. In this paper, the relationship between the reliability index and the capacity factors, also referred to as “resistance factors”, used in design equations of such LVL beams in both edge and flat bending is investigated taking into account the load duration effects (damage accumulation). The relationship is presented for six different beam sizes, four grades and three hardwood species (Gympie messmate (Eucalyptus cloeziana), spotted gum (Corymbia citriodora) and southern blue gum (Eucalyptus globulus)) using the strength distribution of the beams recently quantified by the authors. Parametric studies on five main design load combinations stipulated in the Australian standard and three rates of damage accumulation, based on the data available in the literature, are conducted. Results show that the reliability index is highly sensitive to the damage accumulation rate and that the “Dead + Sustained and Extraordinary live loads” and “Dead + Wind + Sustained live loads” load combinations govern the choice of the capacity factor. Recommendations are made on the appropriate capacity factors to be used for various service categories of structures. The proposed capacity factors are found to be 5%–12% lower than the ones currently used in Australia for the LVL beams manufactured from mature softwood logs, as opposed to juvenile hardwood logs as in the proposed products.

Strain recovery model for concrete after compressive creep

The research objective of this study is to examine the strain recovery of concrete after compressive creep. First, the influences of concrete strength, load duration, and stress-strength ratio at loading time on the initial-recovery are investigated on 128 concrete prisms. The concrete strength, loading age, and load duration have no clear influence on the initial-recovery strain coefficient (the ratio of initial-recovery strain to initial strain) when the concrete age concrete is over 28 d and load duration is over 41 d, but the initial-recovery strain coefficient decreases as the stress-strength ratio at loading time increases. Moreover, the effects of loading age, load duration, and concrete strength on creep-recovery are investigated by examining data from tests and references. The basic creep-recovery model is obtained by fitting the creep-recovery experimental data from 28 concrete prisms. Then, a multi-coefficient creep-recovery model for concrete that considers the influence of creep, loading age, load duration, and concrete strength is proposed. Finally, the proposed creep-recovery model is verified with reference data, with better performance than the existing creep-recovery models.

Effect of NiO Loading and Thermal Treatment Duration on Performance of Ni/SBA-15 Catalyst in Combined Steam and CO<sub>2</sub> Reforming of CH<sub>4</sub>

Effect of NiO Loading and Thermal Treatment Duration on Performance of Ni/SBA-15 Catalyst in Combined Steam and CO<sub>2</sub> Reforming of CH<sub>4</sub>

Effect of loading time on soil structural failure

Identifying compaction potential for varying loads and soil conditions is vital for making management decisions related to crop seed germination, plant growth and crop production. However, the interacting effects of loading and loading duration on compaction related structural integrity were still unclear. Changes in soil water potential have proven to be a useful indicator for evaluating compaction induced changes in soil structure during stress application. The objective for this study was to determine the effect of load and loading time on soil structural degradation of four different soil materials with four different initial gravimetric soil water contents (11, 15, 19 and 24%). Soil structural failure was based on changes in soil water potential relative to the water potential observed for critical stress loads which are the stress associated with soil structural failure. With a fixed load of 4.0 kg/cm2, which approximates the load applied with normal field tractors used in Northeast China, soil water potential decreased with increasing loading time from 0 to 100 s for all soil material and water content combinations. For short term loading, water potential decreases were consistently found for loading times of 1 s or less across all soil materials. For all soil materials, loads applied for 0.1 s accounted for more than 50% of the water potential change that occurred during 1 s load application. Increasing soil water content not only reduced the critical stress value, but also reduced the loading time required to reach critical stress water potential. This finding demonstrates that loading time (0–1 s), approximating that of implement wheels or planter press wheels, reduces soil water potential sufficiently to affect water movement, potentially important for seed germination associated with planter press wheel operation. Additionally, loads that at least marginally exceeding the critical stress static load can be applied for a short time (0–1 s) without causing structural degradation.

Elastic Rebound of a Blast Door Under Explosion Loadings

Rebound effects can be caused for a blast door under explosion loadings of conventional weapons. Such effects reaching a certain extent can lead to severe reversed stresses and even destroy the hinge and lock system before the door leaf. In this study, an analytical model for the elastic rebound of a blast door under explosion loadings was proposed and analyzed. Based on the calculations, the effects of aspect ratio and load duration on the rebound behavior were analyzed. Furthermore, for extension of the analysis from the elastic to plastic range, comparison of the solutions with the analytical ones was made. The results showed that the positive and negative dynamic shear force peaks of the blast door deceased gradually with the aspect ratio, whereas the rebound strength was inversely proportional to the load duration. For blast doors entering into the plastic stage, the rebound behavior was similar to the elastic stage, implying that the design of a blast door can be based on its characteristics in elastic stage.

Assessing bioethanol extraction potential from waste pulps of cassava (Manihot esculenta Crantz) via aerobic fermentation

The advocacy of producing biofuels from wastes would answer the call for energy and environmental sustainability. This call is very timely considering the issues of global warming, increasing greenhouse gas emissions, diminishing natural resources, and enlarging human population. For one, the increasing generation of waste pulps from the growing numbers of starch-producing industries using cassava (Manihot esculenta Crantz) has become alarming because the improper disposal of these causes putrefaction odor, leachate contamination on water bodies, illnesses/diseases of community residents, and so on. In this work, the potential of cassava waste pulps (CWP) from starch industry was assessed with regard to the extraction of bioethanol via aerobic fermentation. The effect of yeast loading (0–4 tsp) and mashing duration (3–11 min) was evaluated on their influence on the bioethanol yield in CWP fermentation through central composite design of the response surface methodology. The result showed that 5.93 ± 0.03 mL of bioethanol could be extracted from a kilogram of fresh CWP after 7-day aerobic fermentation at conditions of 7 min mashing duration (42 °C) and 1 tsp yeast loading. Yeast loading and mashing duration are both significant with regard to bioethanol production. The gas chromatography analysis revealed 0.08% v/v bioethanol in the fermentation broth.

Effects of trimethylamine oxide (TMAO) and loading duration on the shoot tip cryopreservation of loquat (Eriobotrya japonica).

Two cryoprotectant solutions, including trimethylamine oxide (TMAO) and dimethyl sulfoxide (DMSO), and several loading durations were used to evaluate the cryopreservation of the shoot tip of Eriobotrya plants. The best results for regrowth (59.91%) were obtained from 10% TMAO compared to 10% DMSO as cryoprotectant, although nonsignificant differences were found for survival between the two cryoprotectants. We detected pronounced effects of loading duration on survival and regrowth rates of shoot tips. The maximum regrowth (56.36%) was observed at 9 h of loading duration. The cryoprotectants and loading durations greatly affected the regrowth of Eriobotrya shoot tips, and TMAO could be introduced as a nontoxic and efficient cryoprotectant. These results could lay a foundation for the cryopreservation of Eriobotrya.