Predicted Maximum Loads Research Articles

Evaluation method of compression parallel to grain stiffness in wood and relationship between stiffness and shape of contact surface

The compressive behavior parallel to the grain is an essential parameter for the designing of multistoried and large timber buildings. However, the application of a compressive force parallel to the grain results in significant deformations near the end grain, which is referred to as the damage zone. Therefore, this study elucidates the mechanism of the damage zone and proposed a methodology to evaluate the properties of the damage zone. The cause of the damage zone was attributed to an uneven contact surface. As the contact surface shape remained non-flat even after reaching 28% of the predicted maximum load, the initial stiffness of compression parallel to the grain necessitated an assessment based on the influence of the damage zone. The Young’s modulus of the damage zone was approximately 2% of that of the middle zone and an evaluation method for the damage zone length was proposed using the strongest link model. The Young’s modulus and damage zone length evaluation methods were used to evaluate the stiffness of the specimens when compressed parallel to the grain. The proposed method could adequately evaluate the experimental values.

Numerical and experimental investigation of quasi-static indentation response of PVC foam sandwich and GFRP laminated composites

AbstractComposite materials are vulnerable to impacts that may occur during their use. Such transverse loads represent a significant threat to these materials because they can cause damage that is difficult to detect. Thus, understanding the mechanical behavior of composite materials during impacts is crucial for improving their damage resistance. Therefore, this study investigates the response of two commonly used composite panels in maritime transportation—a PVC core sandwich composite and a laminated GFRP composite—under quasi-static indentation (QSI). Using numerical simulations with Abaqus/Explicit, this investigation aims to anticipate mechanical characteristics and damage patterns during low-velocity impact. Results show a strong correlation between numerical and experimental data. The force-displacement curves aid in understanding damage sequences, with predicted maximum loads at 1.43% and 6.45% accuracy for laminated and sandwich composites. Both exhibit significant damage, including permanent indentation, matrix cracks, fiber fractures, and prevalent delamination around the impact point.

Study of conduction welded C-struts for a thermoplastic composite fuselage

In this research, conduction welded C-struts, part of a thermoplastic composite fuselage designed and manufactured in the framework of the Clean Sky 2 STUNNING project, are investigated. Five specimens made of two C-section profiles are manufactured and welded using conduction welding in three different configurations with variations in the direction and distance of the two welded joints. Preliminary numerical analysis using the virtual crack closure technique are conducted to obtain an initial evaluation of the specimens behavior, in preparation of the tests. Experiments are performed under quasi-static loading conditions to measure the strength of the welds. Comparisons with the preliminary numerical analyses show a good agreement in terms of the predicted maximum load, while a clear difference is observed in the initial stiffness, due to the compliance of the support structure. The numerical model is updated, leading to results that closely match the experimental behavior. For all the analyzed specimens, the separation occurs suddenly and no signs of propagation are observed. Experimental and numerical data show no relevant difference in the joint strength among the different conduction welding configurations.

Influence of face sheet thickness on flexural strength characteristics of carbon/epoxy/Nomex honeycomb sandwich panels

This study presents the findings of an investigation into the effect of varying the thickness of a carbon/epoxy face sheet of a Nomex honeycomb sandwich panel on its the flexural properties. The thickness (hs) of the face sheet was varied by increasing the number of plies from one 0.25 mm thick layer to eight such layers, giving a total nominal thickness of 2.0 mm, whilst maintaining a constant thickness of the core. The flexural properties of the sandwich panels were investigated through a series of three- and four-point bending tests. A particular focus was on identifying changes in the failure mode with increasing face sheet thickness. The flexural properties of the sandwich panels were predicted using sandwich beam theory, where the deviation from the experimental values was shown to be less than 13%. A two parameter Weibull distribution model was used to predict the maximum flexural load using an analysis of variance (ANOVA) tool and an excellent level of correlation was observed with the experimental values. The difference between the predicted maximum load values and the experimental results was below 5% in all cases. A brittle mode of failure was observed in the thickest panel. The sandwich panel based on 1.5 mm thick face sheet was identified as being the most appropriate design, both in terms of strength and stiffness.

Three-dimensional failure behaviour of L-shaped laminated composite with wrinkles and defects

In this paper, three-dimension failure behaviour of L-shaped composite beam with manufacturing defects was studied under four-point bending test condition. First, X-ray computed tomography scan was performed for L-shape laminated composite beam specimen to detect manufacturing defects such as voids, pre-delamination, and wrinkles or ply waviness. The scan images were then converted to three-dimensional volumetric entity through image processing, from which finite element mesh was generated with the detected defects directly incorporated. Next, three-dimensional progressive failure analysis was performed for the finite element model of the L-shaped laminate composite simulating four-point bending test condition with delamination and matrix failure in 90 degree plies accounted for by using cohesive zone modelling. The predicted maximum load was well matched to that obtained by tests validating the analysis modeling. Then a series of parametric studies were performed to investigate the effect of defect size and location on the failure load and delamination propagation pattern. It was found that the maximum load reduction was the largest when the pre-defect was located at the center of the symmetrical portion of the L-beam. In addition, the maximum load and delamination development behavior varied significantly depending on the interlayer and in-plane position of the pre-defect.

Investigation of multiple-presence factor for traffic loads on road-rail bridges based on a novel extreme value analysis approach

Multiple-presence factor (MPF) is an efficient measure for calculating traffic load effects on bridges with multiple lanes. It takes into account the probability of multiple heavy vehicles that simultaneously present in adjacent lanes. Though road-rail bridges carrying both road and rail traffic are common in modern cities, no sophisticated method is available to obtain the MPFs for the combined traffic loads. This study presents a novel extreme value analysis approach to predict the extreme load effects on road-rail bridges and investigate the corresponding MPFs. The core of the new approach is an unsupervised clustering algorithm based on a generalized extreme value mixture model (GEVMM), which can fit data with mixed distribution characteristics and can predict extreme values. The road-vehicle flow is represented by vehicle parameters and traffic parameters. The train flow is generated based on the distribution of passenger volume and train schedule. The 1000-day load effects on road-rail bridges with various spans are simulated and then used to predict the maximum load effects in 100 years based on the proposed method and the conventional generalized extreme value (GEV) approach, respectively. The comparison among the predicted maximum load effects and those obtained from the simulated 100-year road-rail traffic flow shows that the proposed approach is more reliable than the conventional GEV approach. Then the MPF values of the road-rail bridges are calculated from the predicted maximum load effects during a specified return period of 2000 years. The proposed method provides a valuable reference for the design and evaluation of road-rail bridges with various spans.

Study on fracture transferability from compact type specimen to pipe for 316LN stainless steel

The transferability of continuum damage parameters for ductile fracture from CT specimen to pipe has been investigated for 316LN stainless steel. The authors have earlier established crack initiation stress and crack evolution energy as damage parameters for 316LN SS, based on coupled experimental and numerical analysis. Using these fracture parameters, XFEM crack growth simulations were carried out for through-wall circumferentially cracked straight pipes of 80NB diameter. To verify the applicability of damage parameters for various crack geometries, the stress triaxiality ahead of a growing crack in CT specimen and through wall crack in pipes has been assessed. The average triaxiality for CT specimen is 1.25 and for the pipes, it varies from 0.4 to 0.62 depending on initial through wall crack size. The predicted maximum load, load-displacement response, crack growth and pipe ovality are compared with the experimental results.

バンプフォイル軸受の理論最大負荷容量に及ぼすトップフォイル変形解析モデルの影響（第2報） ―アイソパラメトリックシェル要素の適用―

バンプフォイル軸受の理論最大負荷容量に及ぼすトップフォイル変形解析モデルの影響（第2報） ―アイソパラメトリックシェル要素の適用―

Relationships between a Load-velocity Profile and Sprint Performance in Butterfly Swimming.

The purpose of this study was to establish the relationships between 50 m sprint swimming performance and variables acquired from a swimming load-velocity profile established by semi-tethered butterfly swimming. Twelve male elite swimmers participated in the present study and performed 50 m sprint and semi-tethered butterfly swimming with different loads. The mean velocity among all upper-limb cycles was obtained from the 50 m swimming (race velocity), and maximum load and velocity were predicted from the load-velocity profile established by the semi-tethered swimming test. There was a very large correlation (r=0.885, p<0.01) and a high intra-class correlation (0.844, p<0.001) between the race velocity and the predicted maximum velocity. Significant correlations were also observed between the predicted maximum load and the 50 m time as well as the race velocity (r=- 0.624 and 0.556, respectively, both p<0.05), which imply that an ability to achieve a large tethered swimming force is associated with 50 m butterfly performance. These results indicate that the load-velocity profile is a useful tool for predicting and assessing sprint butterfly swimming performance.

Sizing and Allocation of Battery Energy Storage Systems in Åland Islands for Large-Scale Integration of Renewables and Electric Ferry Charging Stations

The stringent emission rules set by international maritime organisation and European Directives force ships and harbours to constrain their environmental pollution within certain targets and enable them to employ renewable energy sources. To this end, harbour grids are shifting towards renewable energy sources to cope with the growing demand for an onshore power supply and battery-charging stations for modern ships. However, it is necessary to accurately size and locate battery energy storage systems for any operational harbour grid to compensate the fluctuating power supply from renewable energy sources as well as meet the predicted maximum load demand without expanding the power capacities of transmission lines. In this paper, the equivalent circuit battery model of nickel–cobalt–manganese-oxide chemistry has been utilised for the sizing of a lithium-ion battery energy storage system, considering all the parameters affecting its performance. A battery cell model has been developed in the Matlab/Simulink platform, and subsequently an algorithm has been developed for the design of an appropriate size of lithium-ion battery energy storage systems. The developed algorithm has been applied by considering real data of a harbour grid in the Åland Islands, and the simulation results validate that the sizes and locations of battery energy storage systems are accurate enough for the harbour grid in the Åland Islands to meet the predicted maximum load demand of multiple new electric ferry charging stations for the years 2022 and 2030. Moreover, integrating battery energy storage systems with renewables helps to increase the reliability and defer capital cost investments of upgrading the ratings of transmission lines and other electrical equipment in the Åland Islands grid.

Effect of Analytical Model of Top Foil Displacement on Predicted Maximum Load Carrying Capacity of Bump Foil Journal Bearings (Part 1)

Effect of Analytical Model of Top Foil Displacement on Predicted Maximum Load Carrying Capacity of Bump Foil Journal Bearings (Part 1)

다양한 정규화 방법에 따른 평일 단기 전력수요예측 정확도 분석

The short-term load forecasting is necessary for stable and smooth power system operation. The accuracy of short-term load forecasting for weekdays according to various normalization methods is analyzed. The normalization methods to be analyzed are maximum and minimum normalization, maximum normalization, and Z-Score normalization. And the model used for 24-hours load pattern prediction is the exponential smoothing technique. In order to return the normalized 24-hour load value to the load value, the predicted maximum load, minimum load, average load and standard deviation of load are estimated using exponential smoothing. In the recent three-year case studies, the accuracy of the short-term load forecasting applying maximum normalization, maximum and minimum normalization and Z-Score to the exponential smoothing technique is analyzed based on the mean absolute percentage error(MAPE). The test results show that the maximum and minimum normalization method is better than the others.

Biomechanical Characteristics of Osteoporotic Fracture Healing in Ovariectomized Rats: A Systematic Review.

Biomechanical tests are widely used in animal studies on osteoporotic fracture healing. However, the biomechanical recovery process is still unknown, leading to difficulty in choosing time points for biomechanical tests and in correctly assessing osteoporotic fracture healing. To determine the biomechanical recovery process during osteoporotic fracture healing, studies on osteoporotic femur fracture healing with biomechanical tests in ovariectomized rat (OVX) models were collected from PUBMED, EMBASE, and Chinese databases. Quadratic curves of fracture healing time and maximum load were fitted with data from the analyzed studies. In the fitted curve for normal fractures, the predicted maximum load was 145.56 N, and the fracture healing time was 88.0 d. In the fitted curve for osteoporotic fractures, the predicted maximum load was 122.30 N, and the fracture healing time was 95.2 d. The maximum load of fractured femurs in OVX rats was also lower than that in sham rats at day 84 post-fracture (D84 PF). The fracture healing time was prolonged and maximum load at D84 PF decreased in OVX rats with closed fractures. The maximum load of Wister rats was higher than that of Sprague-Dawley (SD) rats, but the fracture healing time of SD and Wister rats was similar. Osteoporotic fracture healing was delayed in rats that were < = 12 weeks old when ovariectomized, and at D84 PF, the maximum load of rats < = 12 weeks old at ovariectomy was lower than that of rats >12 weeks old at ovariectomy. There was no significant difference in maximum load at D84 PF between rats with an osteoporosis modeling time <12 weeks and > = 12 weeks. In conclusion, fracture healing was delayed and biomechanical property decreased by osteoporosis. Time points around D95.2 PF should be considered for biomechanical tests of osteoporotic femur fracture healing in OVX rat models. Osteoporotic fracture healing in OVX rats was affected by the fracture type but not by the strain of the rat.

Prediction of Load-Carrying Capacity in Steel Shear Wall with Opening Using Artificial Neural Network

The effects of different parameters on steel plate shear wall (SPSW) are investigated. The studied parameters are thickness of plate, location of the opening, thickness of diagonal stiffeners, and thickness of circular stiffener. Load-carrying capacity of the SPSW is studied under static load using nonlinear geometrical and material analysis in ABAQUS and the obtained simulation results are verified. An artificial neural network (ANN) is proposed to model the effects of these parameters. According to the results the circular stiffener has more effect compared with the diagonal stiffeners. However, the thickness of the plate has the most significant effect on the SPSW behavior. The results show that the best place for the opening location is the center of SPSW. Multilayer perceptron (MLP) neural network was used to predict the maximum load in SPSW with opening. The predicted maximum load values using the proposed MLP model were compared with the simulated validated data. The obtained results show that the proposed ANN model has achieved good agreement with the validated simulated data, with correlation coefficient of more than 0.9975. Therefore, the proposed model is useful, reliable, fast, and cheap tools to predict the maximum load in SPSW.

Instrumented Mechanically Stabilized Earth Wall Reinforced with Polyester Straps

A wall of mechanically stabilized earth (MSE) with large concrete panel facing, reinforced with polyester straps, is an emerging technology in the United States. To enable the design of this wall system through AASHTO's methodology, the system's classification of extensibility must be established. Therefore, a section of such a wall was instrumented as part of a newly constructed interchange on I-95 at Christiana, Delaware. The section was one of several similar walls that allow access to bridges composing the interchange. Monitoring included tensile force distribution at selected straps and force at the connection of a few straps to the large concrete panels. The recorded data were from April 2012, the beginning of construction of the instrumented wall, to June 2014, about 20 months after construction ended. When this reinforced wall system was classified as extensible, the maximum load in the straps and connections was about one-fourth the predicted value from using the AASHTO method, and the lengths of the reinforcing straps were adequate to enable the wall to sustain the required loads. The indicated conservatism of the measured versus the predicted maximum load in the reinforcements was attributed to significant underestimation of the reinforced soil strength in AASHTO's design and, potentially, to a large toe resistance. The data suggest that AASHTO's design, which is based on extensible reinforcement for this family of MSE walls, is adequate.

Fracture assessment for electron beam welded damage tolerant Ti-6Al-4V alloy by the FITNET procedure

Fracture assessment of the cracked structures is essential to avoiding fracture failure. A number of fracture assessment procedures have been proposed for various steel structures. However, the studies about the application of available procedures for titanium alloy structures are scarcely reported. Fracture assessment for the electron beam(EB) welded thick-walled damage tolerant Ti-6Al-4V(TC4-DT) alloy is performed by the fitness-for-service(FFS) FITNET procedure. Uniaxial tensile tests and fracture assessment tests of the base metal and weld metal are carried out to obtain the input information of assessment. The standard options and advanced options of FITNET FFS procedure are used to the fracture assessment of the present material. Moreover, the predicted maximum loads of compact tensile specimen using FITNET FFS procedure are verified with the experimental data of fracture assessment tests. As a result, it is shown that the mechanical properties of weld metal are inhomogeneous along the weld depth. The mismatch ratio M is less than 10% at the weld top and middle, whereas more than 10% at the weld bottom. Failure assessment lines of standard options are close to that of advanced option, which means that the standard options are suitable for fracture assessment of the present welds. The accurate estimation of the maximum loads has been obtained by fracture assessment of standard options with error less than 6%. Furthermore, there are no potential advantages of applying higher options or mismatch options. Thus, the present welded joints can be treated as homogeneous material during the fracture assessment, and standard option 1 can be used to achieve accurate enough results. This research provides the engineering treatment methods for the fracture assessment of titanium alloy and its EB welds.

Energy loss in a unidirectional flax-polyester composite subjected to multiple tensile load–unload cycles

Composites reinforced with plant fibres show inelastic deformation under tensile loads. This property can be exploited in vibration-damping applications. Inelastic deformation was characterised for composites made from unsaturated polyester resin reinforced with unidirectional flax yarns. The primary yield point was found at a strain of 0.17%, with additional minor yielding events to a strain of 1.0% and then linear deformation to failure at a strain of 1.9%. Inelastic deformation accounted for approximately half of the total deformation across the final half of the stress–strain curve. Energy loss was greatest in the first load-unload cycle, with little change beyond the second cycle. The ratio of lost energy to stored energy settled to values between 0.23 and 0.40 for load-unload cycles peaking at between 15 and 75% of predicted maximum load. Failure stress remained unchanged after 2 × 104 load-unload cycles to approximately 50% of the breaking load. Results were consistent with kink bands straightening when fibres were first loaded, causing partial debonding at the fibre-matrix interface. Energy loss in subsequent cycles was attributed to friction between microfibrils within the kink bands as they twisted and untwisted.

Effect of Detachment and Attachment of Top Foil on Predicted Maximum Load Carrying Capacity of Bump Foil Journal Bearings(Part 2: Extensive Survey of Bearing Design Variables)

Bump foil journal bearings are prospective applicants that can support small-sized high-speed rotating machinery. In the previous report, the maximum load carrying capacity of the bearing was predicted, considering the detachment of top foil and the style of attachment of its trailing edge to the bearing housing, and these effects on the capacity were shown to be small. However, the result was obtained only from a base case of the bearing design variables. In this report, the capacity is presented extensively in other cases of the bearing design variables. It is found that the result is applicable to the capacity of the bearing where an excessive static friction acts between the top and the bump foils. On the other hand, the effects of the detachment and the attachment on the capacity of the bearing without the friction between the two foils could be large in the cases of larger values of rigidity of top foil, preload factor, attached angle of top foil, width diameter ratio and pitch angle of bump-equivalent springs.

バンプフォイル軸受の安定限界速度に対する軸受設計変数の影響(&lt;特集&gt;D&amp;D 2008)

Bump foil journal bearings are prospective applicants for machine elements that can support a small-sized rotor of high-speed rotary machinery. The authors have proposed two models to the bearing, one of which corresponds to the bearing with an excessive static friction between the top and the bump foils and the other to the bearing without the friction. The variation of predicted maximum load capacity of the bearings with respect to the assembly preload was in qualitatively good agreement with the measurement. This study aims at predicting the effect of the design variables of the bearing on the stability threshold speed of the horizontal rigid rotor supported in the model bearings. The modified stability charts show that the effect of two of the variables, the attached angle and the angular extent of top foil, is noticeable, the other two variables, the rigidity of top foil and the equivalent spring constant of bump foil, is modest and the rest of the variables, the density and the thickness of top foil and the pitch angle of bump foil, is negligible. It is also found that the models have to be modified, considering that the top foil is detached from the bump foil.

513 動圧型気体フォイル軸受の最大負荷容量に対する組立て予圧の影響

513 動圧型気体フォイル軸受の最大負荷容量に対する組立て予圧の影響