Vincent Caccese

Experimental methods to determine in-plane material properties of polyurethane-coated nylon fabric

Experimental procedures have been developed to obtain the mechanical stiffness and strength properties of an orthotropic polyurethane-coated nylon fabric for use in a finite element analysis of an inflatable, deployable structure. A method that utilizes a specialized material test fixture and photogrammetry to collect the linear and angular displacement data has been employed. Different material holding methods were compared with the objective of producing strength values not influenced by gripping and that allow for use of machine displacement to estimate longitudinal strains during cyclic testing. A series of tension and bias tension tests provided material properties such as Young’s modulus in both warp and fill directions, Poisson’s ratios in plane and through the thickness, and shear modulus. Results obtained from the photogrammetry method show good correlation to machine readings using a pinched gripping method. Additionally, cyclic tests gave the continuous load–unload response and the hysteresis characteristics of the stress–strain in plane and indicated the degree of material degradation. The shear stress–shear strain behavior and shear modulus values are acquired using bias tension tests on 45° skewed specimens.

Elastic Coupling Effects in Tapered Sandwich Panels with Laminated Anisotropic Composite Facings

A newly developed theory for the analysis of tapered sandwich panels with laminated anisotropic facings is presented. Unlike sandwich panels of uniform depth, the response of tapered sandwich panels is counterintuitive. For example, prior studies have demonstrated that a tapered cantilever sandwich beam having constant dimensions at the clamped edge and subjected to a tip load has an optimum taper angle where the tip deflection is a minimum. The decrease in tip deflection with increasing taper angle, despite the reduction in core thickness, is due to the participation of the facings in resisting transverse shear loads. In the present work, we systematically develop a tapered sandwich theory that is simple to use, yet accurately predicts the stresses and deflection of both symmetric and nonsymmetric tapered sections. A novel feature of the analytical model is that the elastic rigidities of tapered sandwich composites are expressed in terms of the familiar A, B, and D matrices that are widely used to analyze the response of laminated plates and sandwich beams of uniform depth. It is shown that the stiffness matrix for a tapered sandwich member exhibits a total of 12 elastic couplings that are absent in sandwich beams of uniform depth. The analytical model predicts large interlaminar shear and normal stresses near the root of the tapered sandwich beam, which can cause delamination failure between the facings and the core. Numerical results obtained using the tapered sandwich theory and two-dimensional finite element models are in good agreement for several case studies.

EARTHQUAKE SIMULATION TESTING OF SMALL-SCALE REINFORCED CONCRETE STRUCTURES

A brief summary of techniques used in earthquake simulation testing of small-scale concrete structures is presented. Actual prototype concrete structures tend to be very heavy, and even small-scale replicas of these present weight problems for many of the existing earthquake-simulator test facilities. Nonlinear, ultimate strength models need to be employed in this type of shaking table investigation. Included is a discussion of similitude, model materials, distortion of mass density scale, and choice of scale factor. A case study of a 7-story 1:5 scale, concrete wall-frame building tested at the University of California, Berkeley, and a case study of several 5-story, 1:32-scale, isolated precast shearwalls tested at Drexel University are discussed. Knowledge gained from studies such as these is important in understanding the behavior of structures under earthquake loading and will help facilitate the development of earthquake-resistant design.

Evaluation of effective mass during head impact due to standing falls

The objective of this study is to determine the effective mass of a head impact during a standing fall using a HumaneticsTM HYBRID III 5th percentile female and a 50th percentile male anthropomorphic test dummy (ATD). The ATDs were instrumented with an array of tri-axial accelerometers and dropped from different initial positions onto a force plate. Five scenarios of falls were conducted to study the effect of fall direction/type on the effective mass of the head impact. The effective mass for forward and backward standing falls can be estimated as the mass of the head plus 49% and 47% of the neck mass for the female and male ATDs. The lateral fall showed different response where less of the neck mass is involved resulting in an effective mass, which includes the mass of the head plus 6% and 22% of the neck mass for the female and male ATDs, respectively.

Experimental determination of shear properties, buckling resistance and diagonal tension field of polyurethane coated nylon fabric

Experimental methods have been employed to acquire shear properties, examine buckling, and postbuckling response, and to characterize out-of-plane deformations of thin orthotropic polyurethane-coated nylon fabric designated for use in the finite element analysis of an inflatable structure. A custom-designed bi-axial pre-tension frame, a picture-fame rig, and a photogrammetry system were used to apply pre-tension, collect the angular and linear displacements, and to capture the buckling and wrinkle-forming mechanisms in the coupons during the shear test. The series of monotonic picture-frame tests provided with an average critical shear stress of 0.16 MPa that was required to buckle the coupons for a small range of the pre-tension force. While an average pre-buckling shear modulus (28.5 MPa) was obtained, only 2.25% of a relative difference between the average post-buckling apparent shear modulus (13.07 MPa) and the average shear modulus obtained from the 45° bias-extension test for the same material (13.36 MPa) was registered. The influence of the pre-tension not only on the initial buckling resistance and the transition point to the fully developed diagonal tension folds but also on a reduced resistance to the material damage during cyclic testing was investigated. A series of cyclic picture-frame tests gave the continuous load/unload response with appreciable hysteresis characteristics of the in-plane stress–strain with an average 10% of material degradation. When compared with the envelope of material resistance in the monotonic tests, during cycling loading, the coupons lost on average 13.9% more of its initial stress-carrying capability. The photogrammetry results allowed for the three-dimensional reconstruction of the coupon’s surface and the development of the deformation relationships between the effective force exerted on the coupons, the shear angle, and the geometric deformation variables for the wrinkles formed in the diagonal tension fold. The geometric deformation parameters, such as frequency of wrinkle formation, widths of the base and the tip, depths, the deformation angle, and the distances between the centerlines of the wrinkles occurring in the test coupon, were acquired with photogrametry and analyzed numerically with custom-written Matlab® code.

Characteristics of Falling Impact of Head Using a Test Dummy

Traumatic Brain Injury (TBI) contributes to a major number of deaths and cases of permanent disability each year. Falls are the leading cause of TBI with the highest rates for children 0–4 years old and for adults age 75 and older. Accordingly, there is a significant interest in fall-related injury mechanism and head impact. Since the dynamics of human fall and head injury mechanisms are highly variable due to the inherent and complex nature of human falling, the aim of the present study is to describe the dynamics of backward falls and risk of injury due to head impact. In order to have a better understanding of head impact, A HYBRID III 5th Percentile Female test (Denton ATD, Inc.) instrumented with a tri-axial accelerometer with measuring range of ±500g at the center of gravity of the head was dropped from standing posture by using a controlled release mechanism. The dynamic model of fall was captured using a T-series Vicon motion capture system synchronized with a force plate to measure the impact force and a tri-axial accelerometer to measure the impact acceleration of the head. The acceleration impact data measured at 20 KHz and the motion capture system was capable to retrieve 500 samples per second. The primary objective of this study was to determine the equivalent mass involved during head impact due to a backward fall. This effective mass is a key quantity to design the head impact experimental setups, protection devices and computer simulations of head impact. Based on the force and acceleration measurements in several tests, the head impact effective mass is approximately found to be the mass of head itself plus 48% the neck mass. Two scenarios of backward fall were studied and discussed. First, falling while the hip joints are involved and the trunk moves forward and second, falling while the hip joints act like a fixed joint. For the first scenario the impact forces and accelerations peak measured using the HYBRID III were found to be 10±1.8KN and 255±42g, respectively, and for the second scenario the larger impact forces, 14.5±0.9KN, and acceleration peaks, 364±27g, were measured in all tests.Copyright

Cavitation erosion resistance of various material systems

Abstract Advancement in both the design and construction of high-speed ships necessitates the evaluation of cavitation erosion resistant materials. Given their weight advantages, aluminum and laminated composite materials are often chosen as construction materials for high-speed designs. Historically, neither of these materials performs well in a cavitating environment. The objective of this effort is to evaluate potential cavitation erosion protection alternatives. Screening of the various material alternatives was performed using a modified ASTM G32 ultrasonically induced cavitation test method. A relative ranking is provided for materials including metals, composites, elastomers, polymers, and hard ceramic coatings using the maximum erosion rate as a parameter. A potential solution identified during this study involves the use of a durable elastomer material as a protective barrier. Results also show that a sandwich core composite system can be used to increase the cavitation erosion resistance of laminated composite materials.

Development of magneto-rheological fluid composites with rigidification characteristics

Magnetic and magneto-rheological materials have been widely used in many engineering applications. The smart magnetic materials addressed in this study consist of magnetically activated composites made from a core layer of a carrier-material-like fabric, sponge and silicone in combination with small magnetizable ferrous particles suspended in a magneto-rheological fluid. Composite materials that contain magnetic and magneto-rheological ingredients are presently becoming very popular in shape and structure control solutions in a variety of engineering applications. The magneto-rheological response in smart materials allows for the real-time adaptation of material properties. Adequately designed magneto-rheological or magnetic composites are required to perform under different load conditions and provide some rigidification in a sample or a structure. Three different composites are developed in this study including: magneto-rheological fabric composites (MR/FC), magnetic elastomers (M-elastomers) and magneto-rheological sponge composites (MR/SC). The experimental set-up, including custom-made hardware, software and data acquisition system, is designed to conduct experiments used to quantify the material response in shear, tension and compression. The experimental results show a close correlation between the amount of magneto-rheological material present in the specimen and the final displacements in the samples. The resistance to the shear, compressive or tensile forces increases in the samples with the higher concentration of ferrous particles when subjected to a magnetic field. An increased intensity of the magnetic field allows for a stronger magneto-rheological effect and more stable formation of the ferrous chains inside the composites.

Analysis of a hybrid composite/metal ship hull structural system with removable panels

Abstract This article presents the finite element analysis of a bolted composite/metal hybrid panel assembly subjected to uniform pressure loading. The structure consists of four EG/VE stiffened panels joined together by a hybrid connection configuration. A simplified modeling approach is presented, where effective section properties of the hybrid joint regions are computed according to the behavior of each section. The modeling approach is verified with available experimental data, and the global panel deflections as well as the strains within the bulk of the panels are in good agreement with the test results. Parametric studies are presented to quantify the influence of the geometry of the joint constituents on the global response of the hybrid assembly. The model response is most sensitive to changes in the steel component geometries, while the composite laminate geometry has a modest localized effect at the joint region. This approach is useful for global modeling of hybrid joints in large-scale structures, where extensive detailing of the joint region is unfeasible.

Analysis of leak spectral signatures in pressurized space modules

Pressurized space modules of all types are at risk of depressurization due to leaking air. Leaks may be caused by space debris impact or structural aging and failure overtime. This paper addresses the issue of leak type detection by analyzing airborne ultrasonic waves through Fourier Decomposition and Singular Spectrum Analysis. Depending on the vessel material, size of the leak, and pressure gradient, different waveforms are produced. Once a large number of samples have been recorded, the resulting database is used for detecting leaks and identification of the leak specification. This study includes aluminum, steel, rubber, and plastic.