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Ultra-High Performance Concrete (UHPC) is a product that has improved mechanistic properties as compared to traditional concrete and is defined by the Federal Highway Administrations (FHWA) as having a post-cracking tensile strength of 0.72 ksi with a minimum compressive strength of 21.7 ksi. UHPC has constituents that are used to improve the various properties of the concrete. One such constituent is steel fibers, which help to improve the flexural strength of the concrete and the post-cracking strength. There are a variety of different UHPC mix designs, but for this study, the non-proprietary J3 UHPC mix from the University of Oklahoma was used. This study also sought to determine the optimum fiber content in UHPC for strain hardening and to evaluate whether the cylindrical dogbone specimen offers the greatest potential for the Direct Tension Test (DTT). The cylindrical dogbone was chosen because it has reduced stress concentrations and uniform stress distribution compared to the typical prismatic FHWA specimen. This study examined the effects of different fiber contents (0% to 6%) on the tensile capacity and behavior of UHPC. Upon completion of the testing, it was found that 4% fiber content had the best overall tensile performance for the J3 UHPC mix. A study was also completed in order to show the stress distribution in three different specimen types – a cylindrical dogbone specimen, a 2 inch x 4 inch cylindrical specimen, and a 2 inch x 2 inch x 17 inch FHWA specimen. All three specimens were tested in direct tension and modelled in ANSYS. The results showed that the cylindrical dogbone specimen had lower stress concentrations as compared to the FHWA specimen and improved bonding with the end anchorages compared to the cylindrical specimen due to the enlarged end regions. The cylindrical dogbone specimen is recommended for tension testing of UHPC.

Metal additive manufacturing (AM) is a method to create complex components in a layer-by-layer process. Currently, there is a lack of understanding in the processing-structure-properties-performance relationship, particularly related to defects inherent to the AM process. This work investigates the relationship of process parameters, as-built surface roughness, and mechanical performance for nickel-based superalloy 718 built using laser powder bed fusion. The surface roughness of components built using varied processing parameters was characterized using both nondestructive and destructive measurement techniques. Finite element analysis was used to study the stress concentration on surface profiles. Statistical correlations are presented between contour processing parameters and surface roughness metrics. Results show that destructive measurements are required to expose obstructed features and highly concentrated stress is present on crack-like surface features. The discovered understanding of the surface roughness behavior can be used for further process optimization and to inform the certification and qualification strategy for AM components.

Abstract: Strands and wire ropes are widely used in many civil and mining engineering applications, such as encountered in cable stays for bridges, suspension bridge elements, mooring structures, cranes, ropes for shovels, draglines, and for elevators and mine shaft cages and skips. These ropes are broadly classified as stationary and running ropes depending on whether they are subjected to predominantly tensile loads or both tension and bending, over a sheave. The primary reason for failure in such strands and wire ropes subjected solely to tension are fretting fatigue scenarios, manifest as individual wires rubbing against each other as a load is cyclically applied. For strands and wire ropes also bent over sheaves, the failure is invariably identified at the top of the sheave where the rope comes into maximum contact with the sheave. To this date, research based prediction of fretting induced fatigue life reduction of strands and wire rope has partially but not wholly been investigated. Feyrer (2007) performed milestone direction work in proposing regression models, established through regression coefficients, that could be used to calculate the anticipated fatigue life of strands and wire ropes for tension only, and tension plus bending over sheave specific configuration cases. The collection of regression coefficients established by Feyrer were limited to the cases he proposed, such that the current research here extends that knowledge base, through investigating the effect of sheave to rope diameter ratio, , applied load, , sheave contact length of rope, , and sheave groove radius, . These results were analyzed in a parametric study generating regression coefficients to permit additional strands and wire rope types not included in Feyrer`s original investigation. Specifically 7, 19, 91 and 92-wire strands in tension, independent wire rope core (IWRC) and 6 19 Seale-IWRC wire rope (usually called 6 19 Seale wire rope) in tension were analyzed, and subsequently their predicted cyclic tension fatigue life is obtained using a stress based approach. The behaviour of 7 and 19-wire ropes subjected to both tension and bending over sheaves fatigue were also investigated. In all cases investigated, S-N fatigue regression models were proposed. Since the stress based method used for fatigue life prediction is dependent on a stress concentration factor or stress correction factor, both prediction routes have been compared with subsequent recommendations for practical application. Finite element analysis of the strand or wire rope models yielded the stress concentration and correction factors necessary for the fatigue life prediction.

Ants can carry extraordinarily heavy loads in relation to their weight of up to 1000 times its mass, and the neck joint is the smallest membranous component that bears the full load. Scanning electron microscope (SEM) imaging of the neck region recently obtained by Vienny Nguyen has shown there are nine steps at the interface between soft and hard cuticle materials. This study investigates possible reasons why the interfacial neck region has such inter-digitized structure based on the stress distribution analysis. The neck region is modeled as axisymmetric hollow cylinders with the straight, 1-step, and 9-step interfaces of soft and hard materials. Finite element analysis is carried out to investigate the differences in stress distributions among different interfacial structures when they are subjected to longitudinal tensile load away from the interfaces. The volume of high stress regions are calculated based on a python script, and the results show that the 9-step interface has significantly smaller volume of high stress region than those of the straight or 1-step interface. In addition, the high stress region for the 9-step interface is located so that the catastrophic structural failure can be avoided even if local initiation of fracture is initiated. Therefore, from the purely mechanical point of view, the 9-step interface is less susceptible to complete separation of the interface than the straight or 1-step interface.

This paper presents a parametric study of the stresses in a matrix near a cylindrical inclusion. The Texas Grain Analysis Program (TEXGAP), a finite element approach, is used to model the problem. Eight different models are investigated which establish the stress effects of varying interlayer thickness, varying modulus of elasticity of inclusions and interlayers, and element size. The results, presented as plots of axial stresses, show a definite lowering of the stress in the area of inclusion termination as the interlayer thickness is increased from zero. A further stress decrease is noted with the addition of some inclusion elasticity. Similarly, the stresses also decrease as the interlayer becomes more elastic.