Higher Peak Load Research Articles

Scatter and error estimates in ice loads – Results from virtual experiments

This paper analyses peak ice loads on an inclined, rigid marine structure by using data from 2D combined finite-discrete element method simulations. The aim is look for answers to the questions: what type of distributions do peak ice loads follow, what type of data is needed for their analysis, and how should the data on peak ice loads be collected? In the simulations, an initially continuous ice sheet, modeled as a floating beam, breaks into smaller ice blocks as the sheet is pushed against the structure. Statistical tools were used to analyse the peak ice load distributions, error estimates, and peak ice load occurrences. Load distributions appeared to be right-skewed and thus non-normal. Gumbel distribution appeared to describe the data well. The results show that the large scatter in the ice load data is due to the ice-structure interaction process itself. Due to the scatter, a large number of observations are needed for studying peak ice load statistics: To reliably observe a 15% difference in peak loads due to a single parameter would require more than 80 observations in total. The results showed that high peak loads may occur even in the early stage of the ice-structure interaction process.

Assessment of fatigue crack growth in 316LN stainless steel based on acoustic emission entropy

This paper presents an investigation of assessment of fatigue crack growth (FCG) of 316LN stainless steel using the acoustic emission (AE) monitoring technique. A new AE parameter, i.e. AE entropy, was used for accurate assessment of fatigue damage and prediction of fatigue crack length. The effects of peak load on both FCG and AE behaviors were also discussed by fractographic observations and AE parameter analyses. The results showed that AE entropy is effective for accurately identifying the point of crack initiation and assessing the fatigue damage during FCG of 316LN stainless steel under high noise loading environment. Moreover, two distinct damage stages were distinguished by the characteristics of AE entropy. The source mechanisms of AE entropy for stage 1 were fatigue crack initiation and small crack growth, while the mechanisms responsible for stage 2 were the plastic activities in plastic zone at the crack tip, the formation of micro-voids and the ligaments shearing between these micro-voids. The results also indicated that AE entropy is available for identifying the transition in stress condition from plane strain to plane stress state of specimens under high peak load. In addition, a probabilistic model based on the quantitative relationship between the crack growth size and cumulated entropy was proposed for prognosis of crack growth. Bayesian inference was used to estimate the model parameters and the posterior predictive distribution of crack length. The predictive results showed that the model could accurately predict the measured crack growth lengths in all cases. The proposed model is applicable to stable long crack growth and can be applied under high noise loading environment.

Standing Height as a Prevention Measure for Overuse Injuries of the Back in Alpine Ski Racing: A Kinematic and Kinetic Study of Giant Slalom.

Background:In alpine ski racing, typical loading patterns of the back include a combined occurrence of spinal bending, torsion, and high peak loads. These factors are known to be associated with high spinal disc loading and have been suggested to be attributable to different types of spine deterioration. However, little is known about the effect of standing height (ie, the distance between the bottom of the running surface of the ski and the ski boot sole) on the aforementioned back loading patterns.Purpose:To investigate the effect of reduced standing height on the skier’s overall trunk kinematics and the acting ground-reaction forces in giant slalom (GS) from an overuse injury prevention perspective.Study Design:Controlled laboratory study.Methods:Seven European Cup–level athletes skied a total of 224 GS turns with 2 different pairs of skis varying in standing height. Their overall trunk movement (frontal bending, lateral bending, and torsion angles) was measured based on 2 inertial measurement units located at the sacrum and sternum. Pressure insoles were used to determine the total ground-reaction force.Results:During the turn phase in which the greatest spinal disc loading is expected to occur, significantly lower total ground-reaction forces were observed for skis with a decreased standing height. Simultaneously, the skier’s overall trunk movement (ie, frontal bending, lateral bending, and torsion angles) remained unwaveringly high.Conclusion:Standing height is a reasonable measure to reduce the skier’s overall back loading in GS. Yet, when compared with the effects achievable by increased gate offsets in slalom, for instance, the preventative benefits of decreased standing height seem to be rather small.Clinical Relevance:To reduce the magnitude of overall back loading in GS and to prevent overuse injuries of the back, decreasing standing height might be an efficient approach. Nevertheless, the clinical relevance of the current findings, as well as the effectiveness of the measure “reduced standing height,” must be verified by epidemiological studies before its preventative potential can be judged as conclusive.

Collagen XI mutation lowers susceptibility to load‐induced cartilage damage in mice

Interactions among risk factors for osteoarthritis (OA) are not well understood. We investigated the combined impact of two prevalent risk factors: mechanical loading and genetically abnormal cartilage tissue properties. We used cyclic tibial compression to simulate mechanical loading in the cho/+ (Col11a1 haploinsufficient) mouse, which has abnormal collagen fibrils in cartilage due to a point mutation in the Col11a1 gene. We hypothesized that the mutant collagen would not alter phenotypic bone properties and that cho/+ mice, which develop early onset OA, would develop enhanced load-induced cartilage damage compared to their littermates. To test our hypotheses, we applied cyclic compression to the left tibiae of 6-month-old cho/+ male mice and wild-type (WT) littermates for 1, 2, and 6 weeks at moderate (4.5 N) and high (9.0 N) peak load magnitudes. We then characterized load-induced cartilage and bone changes by histology, microcomputed tomography, and immunohistochemistry. Prior to loading, cho/+ mice had less dense, thinner cortical bone compared to WT littermates. In addition, in loaded and non-loaded limbs, cho/+ mice had thicker cartilage. With high loads, cho/+ mice experienced less load-induced cartilage damage at all time points and displayed decreased matrix metalloproteinase (MMP)-13 levels compared to WT littermates. The thinner, less dense cortical bone and thicker cartilage were unexpected and may have contributed to the reduced severity of load-induced cartilage damage in cho/+ mice. Furthermore, the spontaneous proteoglycan loss resulting from the mutant collagen XI was not additive to cartilage damage from mechanical loading, suggesting that these risk factors act through independent pathways. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:711-720, 2018.

The load tolerance of skin during impact on artificial turf using ex-vivo skin as the readout system

ABSTRACTBackground: Understanding the mechanism of sliding induced skin injuries on artificial turf is important to define preventive measures. Recent findings revealed that high peak loads on the knee and thigh during impact of a sliding tackle are critical for inducing skin injuries. Unfortunately, skin failure data under combined impact load is lacking.Methods: In this study the load tolerance of skin to impact on both dry and wet artificial turf and natural grass is investigated by developing an ex-vivo model, a biaxial load applicator and a loading protocol.Results: The critical shear-normal stress combination at which skin breakdown occurred on dry artificial turf was 38 and 20 N.cm−2. Skin damage on wet artificial turf firstly was noticed at a shear-normal stress combination of 55 and 20 N.cm−2. On natural grass, skin breakdown only occurred at a combined shear and normal stress of 130 and 125 N.cm−2. The thickness of the stratum corneum after impact strongly correlated to the applied mechanical load during impact on dry artificial turf.Conclusion: In contrast to natural grass, skin damage on dry artificial turf is strongly related to the magnitude of the impact load. Wetting of the artificial turf system improves the load tolerance of skin to impact.

Flexural response of carbon fiber reinforced aluminum foam sandwich

Sandwich panels with carbon fiber fabric/epoxy resin face-sheet and aluminum foam core have a potential application value in the engineering field. To study the bending mechanical properties of the reinforced sandwich structure, three-point bending test was conducted by using WDW-T100 electronic universal tensile testing machine. The relation between load and displacement of the aluminum foam sandwich was obtained. Deformations and failure modes of the specimens were recorded. Scanning electron microscopy was used to observe the failure mechanism. Results showed that when aluminum foam was reinforced by carbon fiber fabric as face-sheet, its flexural load-carrying capacity and energy absorption ability improved significantly. Foam core density and number of carbon fiber plies had serious impacts on the peak load value and energy absorption value of the composite structure. It was suggested that aluminum foam core sandwich structure with low foam core density of 0.49 g/cm3 and 5 plies of carbon fiber fabric had the highest energy absorption ability and medium load-carrying ability. Failure modes analysis showed that shear failure leaded to the final failure of sandwich panels with medium peak load and interface de-bonding leaded to the final failure of sandwich panels with high peak load.

Charging electric vehicles, baking pizzas, and melting a fuse in Lochem

To evaluate the impact of the energy transition on distribution grids, a year 2025 scenario stress test was conducted in a real Dutch distribution grid. For this, the authors confronted the local low-voltage grid of a village with 20 electrical vehicles and ovens. The result was a short service interruption which could not be avoided by control. Furthermore, severe unbalance and high peak load were observed, resulting in large voltage drops and severe neutral point shifts. The obtained measurements are used to validate simulation models used to study the effect of novel control strategies to balance the local grid.

Derivation of simplified control rules from an optimal strategy for electric heating in a residential building

In France, 40% of buildings are heated with electrical devices causing high peak load in winter. In this context, advanced control systems could improve buildings energy management. More specifically, optimal strategies have been developed using a dynamic programming method in order to shift heating load, taking advantage of the building thermal mass. However, this optimization method is computationally intensive and can hardly be applied to real-time control. Statistical techniques can be used to derive near-optimal laws from the optimal control results. These rule extraction techniques model the relationship between explanatory variables and a response variable. This paper investigates the use of Beta regression model. This regression-based strategy was able to mimic the general characteristics of the optimization results with a small mean bias error (−6%) and greatly reduce computational effort (150 times faster). Given its simple mathematical formulation, it could be implemented in real-time building systems control.

Temperature field and microstructure characterization of AA6061/H70 dissimilar thermo-compensated resistance spot welds having different joint configurations

Two types of dissimilar AA6061/H70 thermo-compensated resistance-spot-welding joint configuration are designed. Thermal-electric coupled finite element models are built to reveal the temperature field of these two types of joint. An AISI 201 stainless-steel thermo-compensated sheet assists resistance spot welding through heat conduction. The nugget formation is mainly due to conductive heat from this cover sheet when the thermo-compensated sheet is set adjacent to the AA6061 workpiece (type A joint) and is driven by both Joule heat and conducted heat when the cover sheet is set adjacent to the H70 workpiece (type B joint). To ensure the nugget formation, the conducted heat portion requires a long welding time while the Joule heat portion requires a high welding current. The type B joint configuration has higher Cu and Zn contents in the fusion zone, which leads to a high intermetallic content in the Al-Cu-Zn ternary system existing in the nugget. Most type A joints thus have a higher peak load than type B joints in tensile shear tests.

Microstructure and mechanical properties of resistance spot welded in welding-brazing mode and resistance element welded magnesium alloy/austenitic stainless steel joints

An AZ31 Mg alloy and 316L austenitic stainless steel (ASS) were joined via resistance spot welding (RSW) and resistance element welding (REW). The RSW joints were found to be produced through welding-brazing mode, in which the Mg alloy melted and spread on the solid steel, forming a nugget only in the Mg alloy. The microstructure of the nugget consisted of columnar dendritic structure, indicating that columnar-to-equiaxed transition was interrupted. Shrinkage porosity and cracking were also observed in the RSW nugget. In contrast, a two-zone nugget was formed during REW, consisting of a peripheral nugget on the ASS side and the main nugget. Compared with the RSW joints, the REW joints were obtained at lower welding currents, and they exhibited superior mechanical performance, with 63% higher peak load and 9 times higher energy absorption. Irrespective of the welding current, the RSW joints failed in interfacial failure mode, while the failure mode of the REW joints transited from interfacial to pull out with increased welding current.

Start-up strategy using flywheel energy storage for superconducting DC induction heater

PurposeThe purpose of this paper is to propose a hybrid driving system that couples a motor and flywheel energy storage (FES) for a megawatt-scale superconducting direct current (DC) induction heater. Previous studies have proven that a superconducting DC induction heater has great advantages in relation to its energy efficiency and heating quality. In this heater, a motor rotates an aluminium billet in a DC magnetic field and the induced eddy current causes it to be heated. When the aluminium billet begins to rotate, a high peak load torque appears at a low rotation speed. Therefore, driving the billet economically has been a great challenge when designing the driving system, which is the focus of this paper.Design/methodology/approachA hybrid driving system based on FES is designed to provide extra torque when the peak load torque occurs at a low rotation speed, which allows the successful start-up of the aluminium billet and the operation of the motor at its rated capacity. The mechanical structure of this hybrid driving system is introduced. A simulation model was constructed using Matlab/Simulink and the dynamic start-up process is analysed. The influence of the flywheel’s inertia and required minimum engagement speed are investigated.FindingsThe results of this paper show that the hybrid driving system that couples FES and a motor can successfully be used to start the aluminium billet rotating. The flywheel’s inertia and engagement speed are the most important parameters. The inertia of the flywheel decreases with an increase in its engagement speed.Practical implicationsThe cost of the driving system is significantly reduced, which is very important in relation to the commercial potential of this apparatus.Originality/valueA novel start-up strategy for driving the aluminium billet of a superconducting DC induction heater at low speed is proposed based on FES.

Joining aluminum alloy 5052 sheets via novel hybrid resistance spot clinching process

Aluminum alloy 5052 sheets (thickness: 1mm) were joined using a novel method (resistance spot clinching) that combines mechanical clinching and resistance spot welding processes. A pair of molds combine with processing tapes were exerted in this process. The microstructure of the fusion zone under novel process presents more portion of equiaxed dendritic zone compared with that of the resistance spot welded joint, which is due to the different temperature gradient feature during solidification. The mechanical properties of the joints were evaluated via orthogonal trials of tensile shear tests performed on the joints. The results revealed that, even under lower heat input, the load-bearing capacity of the resistance spot clinching joints is superior to that of the traditional resistance spot welding joints. Digital image correlation was used to evaluate the distortion behavior of the weld joints during testing. Compared with the stiffness of traditional joints, the higher stiffness of the resistance spot clinching joint generated a higher tensile stress component in the periphery of the fusion zone during testing (which resulted in a higher peak load).

Development and Testing of an Energy Storage Material/Phase Change Material Enhanced Heat Sink

ABSTRACTA concept of using energy storage material (ESM) or phase change material (PCM) to enhance the heat transfer dissipation by a conventional compact fin-based heat sink is demonstrated. An actual design is developed, fabricated, and tested to demonstrate the heat transfer enhancement. The heat sink is light weight (made with Aluminum) and miniature in size with a total fin length of 26 mm. Test results demonstrated that under a high peak load (4.4 W/cm2) and low duty power cycle (30/55 on/off ratio with a period of 85 sec), the peak temperature at the heating surface with the ESM/PCM heat sink is 5°C lower than that of a conventional heat sink. At the tip of the fin, the peak temperature with the ESM/PCM heat sink is 3°C lower than that of a conventional heat sink. When the external heat transfer coefficient increases (with increase air velocity), the impact of the PCM/ESM on the heat transfer performance is less. A numerical model, based on COMSOL, is developed to provide a theoretical understanding of the experimental observation.

On Selective Activation in Dense Femtocell Networks

Over-provisioned femtocell networks can be used to serve indoor locations that see high peak loads, such as airports or train stations. However, networks designed for high peak loads are mostly under-utilized, which is wasteful from an energy-use perspective. This paper introduces a femtocell selective activation problem. We motivate the use of selective activation in femtocell networks using real femtocell power measurements. We formally define the selective activation problem, and introduce GreenFemto, a distributed femtocell selective activation algorithm. We prove that GreenFemto converges to a locally Pareto optimal solution. Detailed simulations of an LTE wireless system are used to demonstrate the performance of GreenFemto. We find that GreenFemto uses up to 55% fewer femtocells to serve a given load, relative to an existing femtocell power-saving technique. Furthermore, we show that GreenFemto comes within 15% of a globally optimal solution. We conclude that selective activation can be successfully applied to femtocell networks to both reduce power consumption, and reduce outage probabilities.

Fibre failure assessment in carbon fibre reinforced polymers under fatigue loading by synchrotron X-ray computed tomography

In situ fatigue experiments using synchrotron X-ray computed tomography are used to assess the underpinning micromechanisms of fibre failure in double edge notch carbon/epoxy coupons. Observations showed fibre breaks along the 0° ply splits, associated with the presence and failure of bridging fibres, as well as fibres failed in the bulk composite within the 0° plies. A tendency for cluster formation, with multiple adjacent breaks in the bulk composite was observed when higher peak loads were applied, exceeding 70% of the ultimate tensile stress. Ex situ fatigue tests were used to assess the accumulation and distribution of fibre breaks for different loading conditions, varying peak load and number of cycles. A direct comparison with the quasi-static case for an equivalent peak load, considering the same material system and geometry, has shown that fatigue produces a significantly higher number of fibre breaks. This supports the hypothesis that fibre breaks are indeed caused by the load cycling.

The Load Control Strategy of Datacenter

With development of information technology and growth for various types of cloud computing demand, many data centers have been deployed in cities, and their characteristics of high energy consumption, high peak-load are becoming increasingly prominent, which make a huge impact on urban grid. According to workload prediction in different time intervals, this paper proposes a simplified piecewise load control strategy of datacenter, which could reduce power consumption and peak-load by dynamically adjusting the number of working servers and CRACs. Finally, a simple example is used to validate the performance of our strategy.

On Peak Mooring Loads and the Influence of Environmental Conditions for Marine Energy Converters

Mooring systems are among the most critical sub-systems for floating marine energy converters (MEC). In particular, the occurrence of peak mooring loads on MEC mooring systems must be carefully evaluated in order to ensure a robust and efficient mooring design. This understanding can be gained through long-term field test measurement campaigns, providing mooring and environmental data for a wide range of conditions. This paper draws on mooring tensions and environmental conditions that have been recorded (1) for several months during the demonstration of an MEC device and (2) over a period of 18 months at a mooring test facility. Both systems were installed in a shallow water depth (45 m and 30 m, respectively) using compliant multi-leg catenary mooring systems. A methodology has been developed to detect peak mooring loads and to relate them to the associated sea states for further investigation. Results indicate that peak mooring loads did not occur for the sea states on the external contour line of the measured sea states, but for the sea states inside the scatter diagram. This result is attributed to the short-term variability associated with the maximum mooring load for the given sea state parameters. During the identified sea states, MEC devices may not be in survival mode, and thus, the power take-off (PTO) and ancillary systems may be prone to damage. In addition, repeated high peak loads will significantly contribute to mooring line fatigue. Consequently, considering sea states inside the scatter diagram during the MEC mooring design potentially yields a more cost-effective mooring system. As such, the presented methodology contributes to the continuous development of specific MEC mooring systems.

A Novel Method for Resistance Plug Welding of 7075 Aluminum Alloy

This article investigates a novel resistance welding method – resistance plug welding – to weld 7075 aluminum alloy plates. Lap joints were made of two 1-mm thick 7075 aluminum alloy plates with circular holes punched in the center of the lap zone. A filler rod made of 5052 aluminum alloy, which has better resistance spot weldability, was inserted into the hole. The weld formation, microstructure, and mechanical properties of the joints were analyzed and compared with traditional resistance spot welding joints. The results showed that the current density was more concentrated during resistance plug welding (RPW), which led to larger nugget diameters and higher peak loads and energy absorption in a RPW joint. Defects such as hot cracking and pores, which form easily in 7075 RSW joints, were efficiently avoided in 7075 RPW joints because of the superior weldability of the 5052 aluminum alloy. Partial-thickness, pullout, and ductile fractures occurred in RPW joints, whereas interfacial fracture features and brittle fractures were observed in RSW joints.

Optimal Integration of Alternative Energy Sources in Production Systems With Customer Demand Forecast

The objective of this paper is to develop an optimal planning framework for a production system utilizing multisource distributed energy supplies, in order to improve its energy efficiency and to reduce the dependency on grid energy and outage risk. The energy consumption of an automotive seat assembly plant is modeled using a discrete-event simulation, which consumes energy supplied by wind and solar, as well as traditional power grids. Machines can be halted for designed time period to avoid high peak load and operate efficiently in terms of power consumption. On the other hand, the inventory level can be planned by adjusting production goal to better utilize alternative energy and accommodate demand uncertainty using stochastic programming method. The results from case studies show that optimizing waiting time for each process can effectively reduce outage risk while meeting customer demands. Having the optimal production goal to over-produce when alternative energy supply is high can reduce the dependency on grid energy. Also, the benefit of considering predicted future customer demands would have the effect of safety inventory, which can prevent shortages during extremely high customer demand periods.

Strength and drift capacity of squat recycled concrete shear walls under cyclic loading

In order to provide an improved understanding of the behavior of squat reinforced concrete shear walls and promote the application of recycled concrete in structures, six rectangular squat recycled concrete wall specimens were tested under in-plane cyclic loading. The specimens were designed based on Chinese code for design of concrete structures GB 50010-2010, which specified minimum horizontal and vertical reinforcement ratios of 0.25% in web, and vertical reinforcement ratio of 1.0% in boundary element. The main parameters investigated are axial load level and the amount of vertical and horizontal web reinforcement. This research presents the experimental results which include test observation, lateral load versus drift response, and measured strain distribution of vertical and horizontal reinforcement, measured strength and drift capacity of wall specimens. It was found that increasing of axial load level resulted in a higher peak load but less ultimate drift capacity, and increasing of horizontal web reinforcement had small effect on peak load but could improve the drift capacity. In this study, a mixed flexure and diagonal compression mechanism was proposed to reflect the lateral load resisting behavior of squat walls. Particularly, a simplified analytical method was developed to predict the peak loads of squat walls failed in flexure or a mixed flexural–diagonal compression mode, which was proved to accurately predict the peak loads of specimens.