High-density polyethylene pipes are widely used in pressure pipe applications such as water and gas transportation, but both necking and pre-crack effects are still poorly understood. This paper presents experimental observations to highlight strain field evolutions to necking and effects of pre-crack on strain field evolutions in a high density polyethylene material deformed in tension through analyzing spatial distributions of time histories of strains. Necking and its growth along the tension direction dominate the failure behavior of the intact specimen. Necking and crack propagation are both observed in the pre-cut specimen, but the crack propagation eliminates the necking propagation along the tension direction. Energy releases from positions outsides the crack zone lead to the macroscopic load-displacement curve deviates from the trend of the intact specimen. These findings present new recognitions on strain fields evolving to necking and failure induced by the pre-crack that are significant for designing of theoretical models and simulations of polymeric materials and structures.
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The power law acceleration has been validated as an effective method for predicting catastrophic failure time, however, the precursory acceleration distribution in local monitoring signals is still unclear. This paper experimental results to show the variable properties of durations, onset times and critical power law exponents of precursory accelerating deformation with monitoring positions and sizes. Our results declare that precursory strain acceleration at different positions and size windows can provide consistent and stable prediction that agree well with the actual failure time. Our findings suggest that there is an optimal size and monitoring position that present earlier alarm and higher accurate prediction, because of heterogeneity of precursory accelerations in amplitudes and durations.
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While much attention has been given to developing concrete mixtures for digital manufacturing (3D printing) and their associated rheological and mechanical properties, selecting appropriate printing parameters is also crucial for extrusion-based layered manufacturing. This paper explores the impact of layer height, a key parameter affecting rheology requirements, print quality, overall printing time, and interlayer bonding, on the flexural strength and fracture properties of 3D printed beams. This study investigates three-layer heights (LH) (5, 10, and 15 mm) corresponding to 25, 50, and 75% of the nozzle diameter (ND) (20 mm). The results show that smaller layer heights are more beneficial for both unreinforced and fiber-reinforced 3D printed mortars, despite the longer printing times and increased number of interfaces. Furthermore, adding a small amount of steel fiber reinforcement mitigates the adverse effects of weak interfaces on bulk properties. On average, flexural strengths are 30-40% higher, and fracture toughness and crack tip opening displacement are almost 30% higher than plain mixtures. The study employs strain energy release rates, digital image correlation, and optical images/micrographs to explain crack propagation in layered 3D printed mortars under unnotched four-point and notched three-point bending.
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This poster showcases a novel three-actuator fretting fatigue rig that features a horizontal contact orientation. The machine is equipped to conduct tests under lubrication and enables independent control of all loads in terms of intensity and angle phase. To validate this new rig, we performed fretting fatigue tests on a Ti-6Al-4V alloy couple in a cylinder-plane configuration, instrumented with an integrated approach to digital image correlation.
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Yield strength and fracture toughness are often mutually exclusive properties in metals and their alloys. The CrCoNi-based face-centered cubic (fcc) multi-principal element alloys (MPEAs) are known to possess extraordinary high fracture toughness that is enhanced at cryogenic temperatures; however, their relatively low yield strengths limit their engineering applications. This study investigates the role of sub-grain cellular structures in CrCoNi introduced by laser powder bed fusion (LPBF) that enhance its strength, with small compromise to the fracture toughness.
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Tetragraphene (TG) is a quasi-2D semiconductor carbon allotrope composed of hexagonal and tetragonal rings and shows metallic or semiconducting behaviors. This study uses molecular dynamics (MD) simulations to understand fracture properties of triple-layered TG sheets with two different structures under mixed mode I and II loading using the Tersoff–Erhart potential. We investigate the effect of crack edge chirality, loading phase angle, and temperature on the crack propagation path and critical stress intensity factors.
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Adhesive technologies are widely employed in the aerospace and automobile industries due to its advantages over the conventional fasteners. However, the adhesive technologies come with its own shortcomings in bonding two materials together. One of the key challenges in using composites is the occurrence of disbonds. A disbond refers to the failure of an adhesive to fully cure or attach to the adherend surface, leading to a lack of stress transfer at the interface. Achieving a strong bond in such situations can be challenging because it’s difficult to spread the adhesive evenly over the surface. In this study, a numerical framework is considered to evaluate the quantitative and qualitative effect of disbonds on the single lap joints. Finite element technique showed that there was a reduction in the strength of the lap joints as different discontinuities were applied at the joint area.
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Creep in future long-term space technology materials is a critical concern due to the duration of potential missions to Mars and beyond. Structural and skin components in long-term mission spacecraft will undergo creep deformation and eventual failure if not designed to be sufficiently creep resistant. The microstructural deformation mechanisms that control the creep behavior must be understood to intelligently inform the design of new creep resistant alloys and enhance those already in service. Using lightweight single phase β Ti alloys, an analysis tool was developed to measure grain boundary sliding (GBS) and intragranular slip in-situ via a Heaviside function-based algorithm. The data needed for the analysis tool includes an electron backscattered diffraction generated microstructural map and high-resolution digital image correlation (HRDIC) strain fields. This testing technique advances the state of the art by facilitating in-situ measurement of these microstructural deformation mechanisms without the need to interrupt creep testing and introduce unwanted thermic cyclic effects. Proof-of-concept experiments utilizing this analysis tool on a single phase β Ti alloy in room temperature creep rapidly identified the dominant deformation mechanism to be intragranular slip and glide creep without the need for destructive and expensive post-mortem testing.
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Pre-Northridge moment frames with PJP Welded Column Splices (WCS) are highly vulnerable to brittle fracture much before the connection develops the strength of the upper connected column due to the inherent crack-like flaw (unfused region of the weld) and the low toughness of the weld material. Given that the consequences of fracture are catastrophic and that retrofitting these splices can be highly disruptive to building operations, accurately estimating their fracture risk is of great importance. To achieve this, a probabilistic quantification of splice fracture is necessary, along with tools that simulate splice fracture and post-fracture response in a global frame assessment framework.

A framework to probabilistically assess the fracture strength of these splices is presented which addresses shortcomings of previous research and performance assessment guidance that do not consider key mechanistic or statistical effects. A new element model (in OpenSees), which is informed by the fracture mechanics-based estimates of splice strength and existing material models in OpenSees, is developed to simulate the splice fracture and post-fracture response. Application of the new splice element in assessment of a 20-story building to scaled ground motions is demonstrated.
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Ductile fracture is affected by the state of stress, which is commonly described by two parameters, stress triaxiality and Lode parameter. While the effects of triaxiality are well known, the effect of the Lode parameter are uncertain. This uncertainty results in particular from the difficulty to vary the Lode parameter at controlled triaxiality. Recent experiments by the authors suggest that the Lode parameter does indeed affect ductile fracture to some extent. The aim of this work is to analyze the mechanisms behind these apparent effects of the Lode parameter.To accomplish this, an advanced multi-surface porous-plasticity model that accounts for both homogeneous and inhomogeneous yielding is used in an Abaqus Umat to simulate proportional loading of a single integration point. Within this modeling framework, the effect of Lode parameter is inherently captured through the competition between the two main modes of inhomogeneous yielding: internal necking and internal shearing of the intervoid ligament. The ability of this constitutive formulation to capture the effects of the Lode parameter that were observed in experiments is examined.
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