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• An overview of determination of fracture toughness from small punch test is given. • A micro-mechanical model given by Gurson is introduced to predict fracture toughness from small punch test. • Verifications are summarized from three high level institutes. The predicted J IC with that from standard fracture toughness tests are in a good agreement. The main tasks of the small punch (SP) technique are to derive standard material properties from a limited amount of material, including strength/toughness, creep and fatigue behaviour etc. The complicated problem of determining fracture toughness poses significant difficulties. Although many methods have been put forward to increase the prediction accuracy, no satisfactory methods are available yet. Recently, the so-called "Local approach" has been introduced to determine ductile fracture from the small punch test by means of a micro-mechanical model introduced by Gurson and modified by Needleman and Tvergaard. By using the observed load-deflection curve from the small punch test, reverse finite element analysis is performed to identify both the material plastic property (σ-ε curve) and the damage parameters of the Gurson model. With these material parameters known, a standard fracture toughness (CT) specimen is simulated by finite element analyses, from which the J- integral and the crack extension can be estimated. A J-R resistance curve can be created by multiple specimens with different load-line-displacements, and the fracture toughness J IC can be determined according to ASTM E 1820-17. In order to verify this new approach, the standard uniaxial test, the small punch tests and the standard fracture toughness tests are needed with the same material. Up to now, only a few of these kinds of experimental verification are available. In this paper, an overview on the existing methods of determination of fracture toughness from small punch test is given, and the "Local approach" for small punch test is addressed. Verifications are summarized from three high level institutes, including MMT in the Czech Republic, JRC Petten in the Netherlands and EPRI in the USA. The predicted J IC with that from standard fracture toughness tests are compared. A good agreement is found and shows that the "Local approach" is capable of predicting fracture toughness from small punch tests. The prediction accuracy by "Local approach" is better than existing methods. Further work is needed as available tests are still limited. [ABSTRACT FROM AUTHOR]

Abstract: High strength woven fabrics are ideal candidate materials for use in structural systems where high energy absorption is required. One of the more widely used applications for woven fabrics is in propulsion engine containment systems. In this first part of a two-part paper, details of the experiments to characterize the behavior of dry fabrics including Kevlar® and Zylon® are presented. The experimental program to characterize the behavior of 1420 Denier Kevlar® 49 17×17, 500 Denier Zylon® AS 35×35, and 1500 Denier Zylon® 17×17 are discussed. The primary objective is to use the experimental results in the development of a constitutive model that can be used in an explicit finite element analysis program. These include Tension Tests in both the warp and fill directions of the fabric, Trellising Shear Tests and Friction Tests between fabric layers. The results from these tests provide the basis for development of the constitutive model – relating stresses to strains, characterizing failure and interaction between fabric layers. In addition to these basic material tests, tests on systems built with fabric wraps were also conducted. Ballistic tests of containment wraps subjected to a high velocity projectile were carried out at NASA-Glenn Research Center. While these tests provide a comparison between the energy absorbing characteristics of the three fabrics, they also provide benchmark results to validate the developed finite element methodology discussed in the second part of this paper. [Copyright &y& Elsevier]

This paper presents a procedure for the evaluation of the seismic damage in steel moment frame buildings. The rotational capacities, of typical connections of a building in the Los Angeles area, which suffered extensive damage during the Northridge earthquake, were determined using stress triaxiality as an indicator for fracture. The rotational demands of the same connections were obtained from a three-dimensional finite element analysis of the building model. Comparisons of the rotational demands at several locations in the building to the rotational capacities determined by the stress triaxiality analysis showed that fracture of steel moment connections of the building are governed by the triaxiality of stresses. Based on a number of moment connections analyzed, the paper suggests a moment capacity equation for the pre-Northridge welded steel moment connections taking into account the fracture incidence due to stress triaxiality effect. The moment capacity of such connections as dictated by stress triaxiality compared favorably to FEMA-350 requirements. [Copyright &y& Elsevier]

• A splitting resistance equation was proposed for highly prestressed UHPC girders. Ultra-high performance concrete (UHPC) has gained popularity gradually because of its superior mechanical properties, including high compressive and tensile strengths, and exceptional durability. Many researchers have explored the possibility of using long, precast prestressed UHPC girders in buildings and bridges. To do so, the girders generally require a large number of prestressing strands, which causes concern about potential cracking in the end zones at prestress release. Currently, there are no specifications or codes on end zone designs for precast prestressed UHPC girders in the United States. Thus, this paper presents an analytical study that explores highly prestressed UHPC girders' end zone behavior. Finite element analyses were conducted to analyze the end zones of a series of UHPC girders, including one 889-mm-deep and two 813-mm-deep I-girders, and the analysis results were validated with test data. Additional finite element models were developed for other girders with heights of 1,829 mm and 2,743 mm using various reinforcement details. Bursting stress variations in the reinforcement and UHPC were reported based upon the analytical and test results. An equation for splitting resistance attributable to the reinforcement and UHPC was proposed for highly prestressed girders. [ABSTRACT FROM AUTHOR]

Design, fabrication and erection of industrial steel storage rack systems can nowadays take place at different locations, potentially separated by thousands of kilometers. Consequently, manufacturing engineers need to understand the main code provisions adopted in the country where the rack will be in-service. Frequently, design is carried out in accordance with the European (EU) or United States (US) rack codes, which are the most commonly adopted standards for industrial storage systems. As appraisal of the key differences on structural performance associated with the different code provisions in term of storage performance, a previous study of the Authors was focused on storage pallet racks comprised of bi-symmetric cross-section uprights (vertical members). Now, attention is paid to racks with mono-symmetric uprights, typically influenced by relevant warping effects, which are traditionally neglected by rack provisions and, as a consequence, by manufacturing engineers. The design approaches already considered and compared for bi-symmetric uprights now appear to be inadequate and have been necessarily improved, as suggested by the Authors, including at least the contribution due to the bimoment acting along mono-symmetric uprights. Research outcomes, which are discussed in the paper, are related to a parametric analysis on several racks differing for configurations, geometry of components and degree of rotational stiffness of joints. The associated results regarding the four EU and two US considered alternatives are presented and compared directly to each other to allow for a concrete appraisal of the most relevant differences between the admitted design approaches. In order to highlight the importance of warping effects, which can be evaluated only by means of refined finite element (FE) analysis software, design has been undertaken using also the more traditional FE beam formulation implemented in the commercial analysis packages most frequently used in manufacturing offices. Finally, Appendix A presents a complete design example to be used as benchmark, where all the discussed design options are applied and compared to each other. [ABSTRACT FROM AUTHOR]

Approximately 11% of bridges in the United States are categorized as structurally deficient and there is a marked need of more accurately evaluating true structural capacity. Structural Health Monitoring (SHM) systems can provide a timely indication of the need for maintenance, repair, rehabilitation and replacement of bridges and can greatly improve the apportionment and management of limited resources. This paper presents an Automated Ambient Traffic (AAT) approach for determining load rating of bridges monitored by the BECAS SHM system under ambient traffic. The AAT approach was developed through a process integration of truck detection, bridge model calibration, and bridge load rating: (1) the quasi-static bridge strain response and the characteristics of associated trucks are collected; (2) multiple trucks are randomly sampled from a historic Weigh-In-Motion (WIM) database; and (3) for each combination of strain response and truck selection, an Finite Element (FE) model is calibrated and used to calculate a load rating. Sampling strategies were discussed for appropriately quantifying the influence of uncertainties of truck characteristics on the calibration and load rating results. To demonstrate this approach, a sample three-span, five-girder, and two-lane steel girder/concrete deck (I-80) bridge was utilized. A load rating of the I-80 Bridge using the Traditional Known Truck (TKT) approach was performed to provide benchmark results. The results of the calibration and load rating using the AAT approach were derived using three different sampling strategies and compared to those using the TKT approach. The sampling strategy, selecting strain response with a spectrum of higher peak girder strains, associated trucks with a spectrum of higher gross vehicle weights, and two truck events on south and north lanes respectively for a calibration, resulted in the best calibration and load rating results. It was concluded that the AAT approach using the BECAS SHM system is a reliable method for continuously estimating the load carrying capacity of bridges. [ABSTRACT FROM AUTHOR]

Abstract: Breakup model is the key area of space debris environment modeling. NASA standard breakup model is currently the most widely used for general-purpose. It is a statistical model found based on space surveillance data and a few ground-based test data. NASA model takes the mass, impact velocity magnitude for input and provides the fragment size, area-to-mass ratio, velocity magnitude distributions for output. A more precise approach for spacecraft disintegration fragment analysis is presented in this paper. This approach is based on hypervelocity impact dynamics and takes the shape, material, internal structure and impact location etc. of spacecraft and impactor, which might greatly affect the fragment distribution, into consideration. The approach is a combination of finite element and particle methods, entitled finite element reconstruction (FER). By reconstructing elements from the particle debris cloud, reliable individual fragments are identified. Fragment distribution is generated with undirected graph conversion and connected component analysis. Ground-based test from literature is introduced for verification. In the simulation satellite targets and impactors are modeled in detail including the shape, material, internal structure and so on. FER output includes the total number of fragments and the mass, size and velocity vector of each fragment. The reported fragment distribution of FER shows good agreement with the test, and has good accuracy for small fragments. [Copyright &y& Elsevier]

Abstract: Recently, a new suite of twelve benchmark problems for adaptive finite element methods (FEM) was published at the US National Institute for Standards and Technology (NIST). These benchmark problems come with exact solutions, and they exhibit all typical difficulties associated with elliptic problems including singularities, steep internal layers, anisotropy, and oscillations. In this paper we solve these benchmark problems using the open source library Hermes (http://hpfem.org). All these results are reproducible—they are part of the Git repository of the open source Hermes project, and the reader can experiment with them by himself/herself. Instructions for this are provided. We hope that authors of other adaptive FEM codes will make their results for these test problems available in a reproducible fashion as well. [Copyright &y& Elsevier]

Abstract: This paper presents the results of a full-scale load test and a 3D finite element analysis on a two-tier, 5m high, geosynthetic reinforced segmental retaining wall (GR-SRW) subjected to a surcharge load aiming at investigating the response of the GR-SRW to various levels of surcharge load. The results of the load test at working stress condition revealed that the GR-SRW''s response to the test load was well within the serviceability limits, and that the currently available design guideline tends to over-estimate the surcharge load-induced reinforcement forces. The predicted results for the surcharge load well in excess of the test load indicated that the surcharge load-induced reinforcement strains exponentially decrease with depth, showing a good agreement in qualitative terms with that assumed in the FHWA design guideline. The predicted wall deformation at the allowable bearing pressure of 200kPa was within the serviceability level demonstrating an excellent load carrying capacity of the GR-SRW. Design implications and the findings from this study are discussed. [Copyright &y& Elsevier]

Abstract: In this paper, we consider a free boundary problem which arises in the pricing of an American call option. The free boundary represents the optimal exercise price as a function of time before a maturity date. We are developing a parameter estimation technique to obtain both the optimal exercise curve of an American call option and its price. For the numerical solution of a forward problem, a time marching finite element method is adopted. Numerical experiment shows the convergence property of the approximation scheme. [Copyright &y& Elsevier]

Abstract: Unlined reinforced concrete shear walls are often used as ‘tertiary boundaries’ in the United States Department of Energy (DOE) to house dangerous gases. An unanticipated event, such as an earthquake, may cause gases stored inside the walls to disperse into the environment resulting in excess pollution. To address this concern, in this paper, a methodology to numerically predict the gas leakage rate through these shear walls under lateral loading conditions is proposed. This methodology involves finite element and flow rate analysis. Strain distributions are obtained from the finite element analysis, and then used to simulate the crack characteristics on the concrete specimen. The flow rate through the damaged concrete specimen is then estimated using flow rate formulas available from the literature. Results from an experimental specimen are used to evaluate the methodology, and particularly its robustness in the flow rate estimation. [Copyright &y& Elsevier]

Piping elbows under bending are vulnerable to cracking at the crown. Hence it is necessary to estimate the crack driving force. This paper presents a closed form expression for the plastic J-integral for axially through-wall cracked, long radius elbows under opening bending moment. The equation is derived, based on a large number of finite element analyses covering a wide range of geometries. The non-linear finite element analyses were performed using WARP3D software and accounted for geometric and material non-linearity. The material was assumed to follow the Ramberg–Osgood law with a wide range of strain hardening exponent (n=2,3,5,7 and 10). [Copyright &y& Elsevier]