In applications requiring high velocity interactions of energetic materials, the shock response of the crystal-binder interface is of great importance. We demonstrate a technique for capturing the high localized deformation of the crystal-binder interface using time resolved Raman spectroscopy at nanosecond intervals. A bi-crystal interface of polydimethylsiloxane (PDMS) sandwiched between sucrose crystals is used in the method, with the sample as a whole put on a glass surface and impacted from the opposite end. Aluminum cylindrical flyers with thicknesses of 25-50 um and diameters of 1 mm were accelerated utilizing the Laser Induced Projectile Impact Test (LIPIT) to create high velocity shock compression loads. The velocity of the projectiles was determined using heterodyne photon doppler velocimetry (het-PDV) and ranged from 0.5 to 1.5 km/s. Full field measurements of the 532nm Raman spectroscopic response were acquired using an in-house designed laser array configuration with 27 discrete laser subsets. The pressure and temperature distributions over the interface were calculated using the pre-calibrated peak shifts of the sucrose CH and CH2 bonds. The highly localized deformation generated by pressure and temperature rise as the shock front travels across the interface were measured in-situ by the time resolved Raman spectroscopic response. The results showed
EXTENDED ABSTRACT

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.
EXTENDED ABSTRACT

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.
EXTENDED ABSTRACT

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.
EXTENDED ABSTRACT

High cycle fatigue (HCF) in composite structures leads to damage accumulation and associated stiffness
degradation, which are challenging to quantify. This work uses a medium wave infrared to monitor selfheating in chopped carbon fiber/acrylonitrile butadiene styrene specimens subjected to tension-tension
fatigue loading. An innovative rapid testing protocol that correlates the generated full-field temperature
maps and stiffness degradation data has been developed providing a comprehensive understanding of
material behavior under cyclic loading. Results contribute to the fundamental understanding of HCF in
composite materials and develop more accurate predictive models for fatigue life. Rapid testing has allowed
correlating process parameters with the microstructure and structural integrity of additively manufactured
(AM) composites.
EXTENDED ABSTRACT