Patrick M. Schubel

Bio: Patrick M. Schubel is an academic researcher from The Aerospace Corporation. The author has contributed to research in topics: Failure mode and effects analysis & Delamination. The author has an hindex of 8, co-authored 22 publications receiving 602 citations. Previous affiliations of Patrick M. Schubel include Northwestern University.

Low velocity impact behavior of composite sandwich panels

Abstract: Composite sandwich structures are susceptible to low velocity impact damage and thorough characterization of the loading and damage process during impact is important. The objective of this work is to study experimentally the low velocity impact behavior of sandwich panels consisting of woven carbon/epoxy facesheets and a PVC foam core. Instrumented panels were impacted with a drop mass setup and the load, strain, and deflection histories were recorded. Damage was characterized and quantified after the test. Results were compared with those of an equivalent static loading and showed that low velocity impact was generally quasi-static in nature except for localized damage. A straightforward peak impact load estimation method gave good agreement with experimental results. A contact force–indentation relationship was also investigated for the static loading case. Experimental results were compared with analytical and finite element model analysis to determine their effectiveness in predicting the indentation behavior of the sandwich panel.

Impact and post impact behavior of composite sandwich panels

Abstract: Assessing the residual mechanical properties of a sandwich structure is an important part of any impact study and determines how the structure can withstand post impact loading. The damage tolerance of a composite sandwich structure composed of woven carbon/epoxy facesheets and a PVC foam core was investigated. Sandwich panels were impacted with a falling mass from increasing heights until damage was induced. Impact damage consisted of delamination and permanent indentation in the impacted facesheets. The Compression After Impact (CAI) strength of sandwich columns sectioned from these panels was then compared with the strength of an undamaged column. Although not visually apparent, the facesheet delamination damage was found to be quite detrimental to the load bearing capacity of the sandwich panel, underscoring the need for reliable damage detection techniques for composite sandwich structures.

Three-dimensional characterization of textile composites

Abstract: The mechanical and failure behavior of a carbon-fabric/epoxy composite was characterized and appropriate failure criteria in three dimensions were proposed. The material investigated was reinforced with a five-harness satin carbon fiber weave. Test methods were developed/adapted for complete mechanical characterization of textile composites in three dimensions. Through-thickness tensile and compressive properties were obtained by testing short waisted blocks bonded to metal end blocks. The through-thickness shear behavior was determined using a short beam with V-notches under shear. Multiaxial states of stress were investigated by testing in-plane and through-thickness specimens under off-axis tension and compression at various orientations with the in-plane directions. Three types of failure criteria in three dimensions were proposed, limit criteria (maximum stress), fully interactive criteria (Tsai–Hill, Tsai–Wu), and failure mode based and partially interactive criteria (Hashin–Rotem, Sun, NU). The latter, a newly developed interlaminar failure theory, was found to be in excellent agreement with experimental results in the through-thickness direction, especially those involving interlaminar shear and compression.

Response and Damage Tolerance of Composite Sandwich Structures under Low Velocity Impact

Abstract: The deformation and failure response of composite sandwich beams and panels under low velocity impact was reviewed and discussed. Sandwich facesheet materials discussed are unidirectional and woven carbon/epoxy, and woven glass/vinylester composite laminates; sandwich core materials investigated include four types of closed cell PVC foams of various densities, and balsa wood. Sandwich beams were tested in an instrumented drop tower system under various energy levels, where load and strain histories and failure modes were recorded for the various types of beams. Peak loads predicted by spring-mass and energy balance models were in satisfactory agreement with experimental measurements. Failure patterns depend strongly on the impact energy levels and core properties. Failure modes observed include core indentation/cracking, facesheet buckling, delamination within the facesheet, and debonding between the facesheet and core. In the case of sandwich panels, it was shown that static and impact loads of the same magnitude produce very similar far-field deformations. The induced damage is localized and is lower for impact loading than for an equivalent static loading. The load history, predicted by a model based on the sinusoidal shape of the impact load pulse, was in agreement with experimental results. A finite element model was implemented to capture the full response of the panel indentation. The investigation of post impact behavior of sandwich structures shows that, although impact damage may not be readily visible, its effects on the residual mechanical properties of the structure can be quite detrimental.

Towards High-Performance Bioinspired Composites

Abstract: Biological composites have evolved elaborate hierarchical structures to achieve outstanding mechanical properties using weak but readily available building blocks. Combining the underlying design principles of such biological materials with the rich chemistry accessible in synthetic systems may enable the creation of artificial composites with unprecedented properties and functionalities. This bioinspired approach requires identification, understanding, and quantification of natural design principles and their replication in synthetic materials, taking into account the intrinsic properties of the stronger artificial building blocks and the boundary conditions of engineering applications. In this progress report, the scientific and technological questions that have to be addressed to achieve this goal are highlighted, and examples of recent research efforts to tackle them are presented. These include the local characterization of the heterogeneous architecture of biological materials, the investigation of structure-function relationships to help unveil natural design principles, and the development of synthetic processing routes that can potentially be used to implement some of these principles in synthetic materials. The importance of replicating the design principles of biological materials rather than their structure per se is highlighted, and possible directions for further progress in this fascinating, interdisciplinary field are discussed.

Crack propagation in rubber-like materials

Abstract: Crack propagation in rubber-like materials is of great practical importance but still not well understood We study the contribution to the crack propagation energy (per unit area) G from the viscoelastic deformations of the rubber in front of the propagating crack tip We show that G takes the standard form G(v,T) = G0[1+f(v,T)] where G0 is associated with the (complex) bond-breaking processes at the crack tip while f(v,T) is determined by the viscoelastic energy dissipation in front of the crack tip As applications, we discuss the role of crack propagation for adhesion, rolling resistance and sliding friction for smooth surfaces, and for rubber wear