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Fracture characterization of human cortical bone under pure mode I loading was performed in this work. The purpose of this paper is to validate the proposed test and procedure concerning fracture characterization of human cortical bone under pure mode I loading.

A miniaturized version of the double cantilever beam (DCB) test was used for the experimental tests. A data reduction scheme based on crack equivalent concept and Timoshenko beam theory is proposed to overcome difficulties inherent to crack length monitoring during the test. The application of the method propitiates an easy determination of the Resistance-curves (R-curves) that allow to define the fracture energy under mode I loading from the plateau region. The average value of fracture energy was subsequently used in a numerical analysis with element method involving cohesive zone modelling.

The excellent agreement obtained reveals that the proposed test and associated methodology is quite effective concerning fracture characterization of human cortical bone under pure mode I loading.

A miniaturized version of traditional DCB test was proposed for cortical human bone fracture characterization under mode I loading owing to size restrictions imposed by human femur. In fact, DCB specimen propitiates a longer length for self-similar crack propagation without undertaking spurious effects. As a consequence, a R-curve was obtained allowing an adequate characterization of cortical bone fracture under mode I loading.

Composite materials and metallic structures already compete for the next generation of single-aisle aircraft. Despite the good mechanical properties of composite materials metallic structures offer challenging properties and high cost effectiveness via the automation in manufacturing, especially when metallic structures will be welded. In this domain, metallic aircraft structures will require weight savings of approximately 20 per cent to increase the efficiency and reduce the CO₂ emission by the same amount. Laser beam welding of high-strength Al-Li alloy AA2198 represents a promising method of providing a breakthrough response to the challenges of lightweight design in aircraft applications. The key factor for the application of laser-welded AA2198 structures is the availability of reliable data for the assessment of their damage tolerance behaviour. The paper aims to discuss these issues.

In the presented research, the mechanical properties concerning the quasi-static tensile and fracture toughness (R-curve) of laser beam-welded AA2198 butt joints are investigated. In the next step, a systematic analysis to clarify the deformation and fracture behaviour of the laser beam-welded AA2198 four-stringer panels is conducted.

AA2198 offers better resistance against fracture than the well-known AA2024 alloy. It is possible to weld AA2198 with good results, and the welds also exhibit a higher fracture resistance than AA2024 base material (BM). Welded AA2198 four-stringer panels exhibit a residual strength behaviour superior to that of the flat BM panel.

The present study is undertaken on the third-generation airframe-quality Al-Li alloy AA2198 with the main emphasis to investigate the mechanical fracture behaviour of AA2198 BMs, laser beam-welded joints and laser beam-welded integral structures. Studies investigating the damage tolerance of welded integral structures of Al-Li alloys are scarce.

THE STABILITY CHARTS THE numerical results representing one of the primary aims of this paper are embodied in the 24 charts reproduced on pp. 282–4. These, while possessing some measure of generality, may readily be extended if desired so as to include a wider range of incidences, of inertia coefficients and of t. It is suggested that whenever a lateral stability investigation is made for any particular aircraft, the charts be used for a first approximation, and that this be followed by the construction of fresh E and R curves using the known values of the inertia coefficients and t. For this purpose all that is required is the filling in of one line of a table similar to Table II of Article II, and the drawing of a straight line and a hyperbola by a rapid and accurate method.

The purpose of this paper is to develop a real-time trajectory planner with optimal maneuver for autonomous vehicles to deal with dynamic obstacles during parallel parking.

To deal with dynamic obstacles for autonomous vehicles during parking, a long- and short-term mixed trajectory planning algorithm is proposed in this paper. In long term, considering obstacle behavior, A-star algorithm was improved by RS curve and potential function via spatio-temporal map to obtain a safe and efficient initial trajectory. In short term, this paper proposes a nonlinear model predictive control trajectory optimizer to smooth and adjust the trajectory online based on the vehicle kinematic model. Moreover, the proposed method is simulated and verified in four common dynamic parking scenarios by ACADO Toolkit and QPOASE solver.

Compared with the spline optimization method, the results show that the proposed method can generate efficient obstacle avoidance strategies, safe parking trajectories and control parameters such as the front wheel angle and velocity in high-efficient central processing units.

It is aimed at improving the robustness of automatic parking system and providing a reference for decision-making in a dynamic environment.

This paper describes progress on the development of theoretical models required for studying failure mechanism, crack initiation and growth around the boreholes driven by hydrofracturing processes in Hot Dry Rock (HDR) reservoirs of geothermal energy. Due to the importance of the stress intensity factor concept (K) in Fracture Mechanics, some advanced modeling techniques for accurate and fast determination of K for relevant problems are proposed. Alternative tools to deal with stress intensity factor determination are developed and assessed from the points of view of accuracy and computational cost. We concentrate on residual strength, crack initiation and crack growth as a means to model and understand experimentally observed behaviors. Several modeling methods such as compounding and weight function techniques, and boundary and finite element modeling for stress intensity factor calculation are discussed. Further to reviews of those techniques, work performed included (i) developing alternative solutions to deal with boundary‐to‐boundary interaction when using the compounding technique, (ii) relating the precision of K calculations with the level of precision of the crack opening displacement of a reference solution, in order to assess the precision of weight function technique, (iii) modeling relevant geometries using the finite element method (FEM), (iv) working on the implementation of direct stress intensity factor K determination in the Higher Order Displacement Discontinuity Method (HODDM), and (v) developing tools to deal with residual stress fields around the boundary of the hydraulically pressurized boreholes.

This paper aims to promote a strength model for TiC-TiB2 composite ceramic with non-ellipsoidal particles bridging. Based on the microstructure of TiC-TiB2 composite ceramic, equivalent average residual stress under particles interaction is calculated with the interact direct derivative estimate. Supposing the crack opening displacement keeps ellipsoidal under the TiB2 particles bridging, crack growth resistance curve is obtained.

Composite strength under R-cure with crack unstable propagation is calculated. Based on this model, influences of particles volume fraction, shape, size and other parameters on strength are analyzed.

Results indicated that calculated values are consistent to the tested data. Crack growth resistance increases with crack propagation and TiB2 volume fraction. The TiB2 particle does not pull-out entirely even ceramic fracture. Ceramic strength increases with the TiB2 particle volume fraction, the ratio of platelet diameter and thickness, and it reduces with particle thickness.

Supposing the crack open displacement keeps ellipsoidal under the TiB2 particles bridging, crack growth resistance curve is obtained.

The purpose of this paper is to describe an innovative Parametric and Adaptive Slicing (PAS) technique to be used for generating material addition paths along three-dimensional surfaces.

The method is grounded on the possibility to generate layers starting from multiple reference surfaces (already available in the model or created on purpose). These are used for mathematically deriving a family of parametric surfaces whose shape and spacing (the layer thickness) can be tuned to get the desired aesthetic, technical and functional characteristics. The adhesion among layers is obtained guaranteeing a smooth transition among these surfaces.

The examples described in the paper demonstrate that the PAS technique enables the addition of the material along non-planar paths and, hence, the elimination of the staircase effect. In addition, objects printed using this technique show improved mechanical properties with respect to those printed using standard planar layers.

As the method allows a local control of the material addition/deposition, it can be used to design the mechanical behavior of the objects to be printed.

The technique proposed in this paper overcomes the limitations of currently available adaptive and curved layer slicing strategies, by introducing the possibility to generate layers with a non-constant thickness whose shape morphs smoothly from one layer to another.

VARIATION IN “TYPICAL VALUE” PARAMETERS IT has previously been shown that the effect of freeing the controls on the lateral stability of an aircraft may be taken account of by changes both in the values of the derivatives lp, lr, np and nr (wing), which hitherto have had typcial values, and also of the variables x, y and t themselves. It is therefore desirable to have information on the effect on the stability boundaries of changes in these derivatives. It may also happen that the values of yv and tan Θo in the case of a particular aircraft may be known to differ from those here adopted in the drawing of stability charts. The versatility of these charts (later to be given) will therefore be considerably increased if rules are expounded for assessing the effects of changes in any of those derivatives which were formerly fixed. This we proceed to do.

In editorial peer review systems of journals, one does not always accept the best papers. Due to different human perceptions, the evaluation of papers by peer review (for a journal) can be different from the impact that a paper has after its publication (measured by number of citations received) in this or another journal. This system (and corresponding problems) is similar to the information retrieval process in a documentary system. Also there, one retrieves not always the most relevant documents for a certain topic. This is so because the topic is described in the command language of the documentary system and this command does not always completely cover the “real topic” that one wants to describe. This paper aims to address this issue.

Based on this statement classical information retrieval evaluation techniques were applied to the evaluation of peer review systems. Basic in such an information retrieval evaluation are the notions of precision and recall and the precision‐recall‐curve. Such notions are introduced here for the evaluation of peer review systems.

The analogues of precision and recall are defined and their curve constructed based on peer review data from the journal Angewandte Chemie – International Edition and on citation impact data of accepted papers by this journal or rejected but published elsewhere papers. It is concluded that, due to the imperfect peer review process (based on human evaluation), if we want to publish a high amount of qualified papers (the ones we seek), several non‐qualified papers should also be accepted.

The authors conclude that, due to the imperfect peer review process (based on human evaluation), if we want to publish a high amount of qualified papers (the ones we seek), one will also accept several non‐qualified papers.

The purpose of this paper is to describe an equity management and planning tool used by rural electric cooperatives (RECs) and based on the times-interest-earned ratio (TIER). The objectives of the paper are to construct a mathematical model that provides a rigorous foundation for the TIER approach, modify the approach so the rate of return on equity is a function of the cooperative’s equity position, demonstrate how elements of the model can be used by RECs in setting electric rates that will enable them to accelerate the retirement of member equity, and derive a generalized form of the “modified Goodwin formula” that can be used by both RECs and agricultural cooperatives.

Mathematical and graphical expressions of the TIER approach are developed. Simulations are used to demonstrate how RECs can set electric rates according to a target revolving period. The modified Goodwin formula is generalized to include the payment of cash patronage refunds through use of a growth model of an agricultural cooperative developed in Royer (1993).

This paper demonstrates how TIER analysis and the modified Goodwin formula can be used by cooperatives to aid their decisions regarding debt and equity financing and their choices regarding cash patronage refunds, equity retirement, and growth. The paper demonstrates that cooperatives that fail to recognize the functional relationship between the rate of return on equity and the equity position may substantially underestimate the equity position necessary to meet interest coverage requirements and overestimate their ability to grow and retire equity. It also shows that RECs may be able to make substantial improvements in equity revolvement with only modest increases in electric rates.

The model developed in this paper has been simplified to focus on fundamental financial relationships. To apply this model, cooperatives may need to modify it to accommodate the complexities of their business operations.

TIER analysis can provide a useful equity management and planning tool for both RECs and agricultural cooperatives. It also can be used by lending institutions to assess the financial health of individual cooperative organizations.

Constructing a mathematical model that provides a foundation for TIER analysis, modifying the approach so that the rate of return on equity is a function of the equity position, demonstrating how RECs can use the model to set electric rates according to a target revolving period, and generalizing the modified Goodwin formula so it can be used by agricultural cooperatives are all original contributions.