Cesar Carrasco

A constitutive-microdamage model to simulate hypervelocity projectile-target impact, material damage and fracture ☆

Abstract A set of constitutive-microdamage equations are presented that can model shock compression and the microdamage and fracture that can evolve following hypervelocity impact. The equations are appropriate for polycrystalline metals. For impact at a projectile velocity of 6.0 km/s, numerical simulations are preformed that describe the impact of spherical soda-lime glass projectiles with aluminum 1100 rectangular target plates. Three ratios of the projectile diameter to the target thickness are chosen for the simulations, providing a wide range of damage features. The simulated impact damage is compared with experimental damage of corresponding test specimens, illustrating the capability of the model.

Localization and quantification of damage in a space truss model using modal strain energy

This paper addresses the issue of localizing and quantifying damage using changes in the vibrational characteristics of structures. The method considers the mode shapes of the structure pre- and post-damage measured via modal analysis. Values of the modal shapes are used to compute the strain energy distribution in the structural elements. Using the assumption that the element modal strain energy is the same pre- and post-damage, and characterizing the damage as a scalar quantity of the undamaged stiffness matrix, an expression is obtained for element damage factors that quantify the magnitude of the damage for each mode shape. Due to numerical instabilities in the computation of this expression, filters are applied that overcome some of the instabilities but reduce the true amplitude of damage. The modified-filtered expression was very effective in localizing the actual damage. After localization, the magnitudes of damage are computed using the original unfiltered expression. The method is tested using experimental data from a 3D scale model of a space structure, subjected to 18 different damage scenarios. The damage forms consist of a 180 degree cut (Type I), a 50 percent reduction of the area over one-third the element length (Type II), and a complete cut through the element section (Type III). These types of damages correspond to magnitudes of (alpha) equal to -0.17, -0.5, and -1.0 respectively. The method is ale to detect Type I damage for only one of four cases, Type II for all the three cases and Type III damage for all single and double-location cases, excluding the cases that involves a damage insensitive element.

A review of the Solar Probe Plus dust protection approach

The Solar Probe Plus (SPP) spacecraft will go closer to the Sun than any manmade object has gone before, which has required the development of new thermal and micrometeoroid protection technologies. During the 24 solar orbits of the mission, the spacecraft will encounter a thermal environment that is 50 times more severe than any previous spacecraft. It will also travel through a dust environment previously unexplored, and be subject to particle hypervelocity impacts (HVI) at velocities much larger than anything previously encountered. New analytical methodologies and designs have been developed to meet this environments extreme micrometeoroid protection challenge while also fulfilling the missions low mass requirement. These new analytical capabilities and protection system concepts could produce similar benefits if applied to Earth orbiting and deep space missions. The SPP dust study was developed to overcome the velocity limitations in the existing micrometeoroid and orbital debris (MMOD) analysis capability. In this study, we developed the hydrocode modeling techniques needed to characterize the material behaviors for a high-shock particle impact event. An additional novel development was an algorithm to calculate the particle flux on specific spacecraft surfaces. Our approach predicts particle impacts for a given spacecraft geometry, including the aforementioned effects. In addition, our approach introduces a size-velocity particle correlation, which lowers the shielding needed for a given protection level. This paper covers the new analytical capabilities developed for the SPP dust environment and how they dramatically lower the mass of the protective systems. The paper also discusses the application of these new analytical capabilities to spacecraft protection in the LEO debris field.

Process to Estimate Permit Costs for Movement of Heavy Trucks on Flexible Pavements

A process based on a mechanistic–empirical (ME) analysis was developed to estimate permit fees on the basis of truck-axle loading and configuration as well as the predicted pavement deterioration that they cause. The process was implemented in a software package, Integrated Pavement Damage Analyzer (IntPave). IntPave is a finite element–based program that calculates pavement responses, uses ME distress models to predict performance under any type of traffic load, is capable of comparing the level of distress caused by a heavy truck relative to a standard truck, and accordingly provides a permit fee. On the basis of a parametric study, it was found that, aside from the truck gross vehicle weight and axle configuration, pavement structure and the damage threshold to rehabilitation also heavily affect the permit fee.

Simulations of hypervelocity impact damage and fracture of aluminum targets using a constitutive-microdamage material model

The material damage and fracture of Aluminum 1100 target plates that experience hypervelocity impact by glass projectiles traveling at 6 km/s are simulated using a proposed constitutive-microdamage material model. The model is best suited for polycrystalline metals that are subject to hypervelocity impact at the lower range of velocities. Simulations are performed for three projectile diameter-target thickness ratios that produce a wide range of damage features. The predicted damage is compared with that of the corresponding test laboratory specimens, illustrating the capability of the constitutive-microdamage model.

Damage detection in a stiffened plate using modal strain energy differences

An aluminum stiffened-plate panel resembling aircraft- fuselage construction was tested in the laboratory with a laser doppler velocimeter. The purpose of the test was to extract out-of-plane mode shape data before and after the infliction of damage to evaluate a global NDE damage localization technique. The NDE damage localization technique is based on modal strain energy differences between the undamaged and damaged states. The modal strain energies were computed from bending and twisting curvatures obtained using an iterative bi-variate curve-fit procedure on estimated curvatures obtained from finite differences of the mode shapes. Strain energy differences between pairs of matching modes of the undamaged and damaged structure locate the inflicted damage by indicating increases in the modal strain energy. The damage indications provided by several modes are normalized using a standard norm and fused using an average approach to create damage maps.

Use of hydrocode modeling to develop advanced MMOD shielding designs

A multi-physics computations-based methodology for space debris hypervelocity impact (HVI) damage mitigation is presented. Specifically, improved debris mitigation through development of innovative, lightweight structural designs is described. The methodology has been applied to the design of the Solar Probe Plus (SPP) spacecraft to mitigate extreme solar microdust hypervelocity impacts (50-300 km/s) by the Johns Hopkins University Applied Physics Laboratory (JHU/APL). The methodology combines hydrocode computations of the complex, early-time transient material and structural responses with experimental hypervelocity impact data to directly obtain end-state damage predictions for the requisite hypervelocities that are in excess of available test capabilities (~10 km/s). The computations are validated in the low-velocity regime (<;10 km/s) by direct HVI testing and verified in the high-velocity regime (50-300 km/s) by comparisons with bounding energy calculations and extrapolations of Ballistic Limit Equations (BLEs). In addition to hydrocode computations, HVI experimental data and supporting structural/solid mechanics analyses are used to define the eventual damage. In addition to being able to treat realistic hypervelocities and spacecraft materials in layered and Whipple configurations systematically, the methodology provides the margin of safety for any design. Sample lightweight design calculations involving state-of-art and innovative protective materials are presented to demonstrate the methodology and its benefits.

Modeling of Slab-Foundation Friction in Jointed Concrete Pavements Under Nonlinear Thermal Gradient or Traffic Loads

The accurate modeling of the thermomechanical response of jointed concrete pavements is of primary importance in the design of pavement sections. From the initial development of pavement analysis software in the early 1970s, it was recognized that the finite element method was the most appropriate modeling tool because of its potential ability to capture all pavement response features. A series of software development efforts have culminated in the production of NYSLAB, an analysis tool for jointed pavement that can predict the complete thermomechanical response, including pavement curling and interactions between slab and foundation. A series of studies were developed in NYSLAB specifically to look into slab–foundation friction generated by nonlinear thermal gradients and traffic loads. Nonlinear temperature gradients can produce slab expansion and contraction that lead to frictional traction between slabs and foundation. The prediction of these friction tractions is complicated by the curling of the slabs that cause some portions of the slabs to lose contact with the foundation. The results of the studies highlight the importance of considering these frictional tractions in the analysis of jointed concrete pavements because they have a significant impact on the bending stresses of portland cement concrete slabs.

Development of NYSLAB

Since the development of ILLI-SLAB software in 1979, researchers have made significant contributions to the capabilities of tools for jointed-pavement analysis. These efforts have culminated in some commercial and noncommercial software packages such as JSLAB and ISLAB2000. Even though JSLAB has undergone several improvements since 1986, the underlying core of the software maintains the characteristics of the initial ILLI-SLAB code. A thorough review of JSLAB2004 revealed that it would be beneficial to redesign the software completely to take advantage of modern computer resources and finite element modeling techniques available today. For this reason, a new analysis tool was developed that significantly improves on the efficiency and capabilities of JSLAB2004. The improvements led to NYSLAB, a tool that (a) has no limitations on the number of jointed slabs and foundation layers analyzed, (b) more accurately models the contact between debonded slabs and between the bottom slab and the top foundation layer, (c) models the foundation layers beyond the edge of the slabs to predict more accurately the edge deflections and stresses, and (d) significantly improves the capabilities for modeling a nonlinear thermal profile on all slab layers to predict more accurately their curling response. A series of parametric studies was conducted to evaluate the performance of NYSLAB and highlight the new and improved capabilities.

A collaborative, interdisciplinary initiative for a smart cities innovation network

A smart city is characterized by its ability to integrate people, technology and information to create a sustainable and resilient infrastructure that provides high quality services for residents. Transforming a city into a smart city requires collaborative efforts between government, industry, practitioners, residents and researchers. This paper describes how researchers in a recently formed consortium of three universities are developing a smart cities innovation network, with an emphasis on smart mobility, smart buildings, and smart bridges. The consortium is applying a semantic-based approach to address the initial challenge of building an effective interdisciplinary network of university researchers located in different parts of the world, in three cities with different sizes and stages of economic development.