John C. Hermanson

A Mechanical Signal Biases Caste Development in a Social Wasp

Understanding the proximate mechanisms of caste development in eusocial taxa can reveal how social species evolved from solitary ancestors. In Polistes wasps, the current paradigm holds that differential amounts of nutrition during the larval stage cause the divergence of worker and gyne (potential queen) castes. But nutrition level alone cannot explain how the first few females to be produced in a colony develop rapidly yet have small body sizes and worker phenotypes. Here, we provide evidence that a mechanical signal biases caste toward a worker phenotype. In Polistes fuscatus, the signal takes the form of antennal drumming (AD), wherein a female trills her antennae synchronously on the rims of nest cells while feeding prey-liquid to larvae. The frequency of AD occurrence is high early in the colony cycle, when larvae destined to become workers are being reared, and low late in the cycle, when gynes are being reared. Subjecting gyne-destined brood to simulated AD-frequency vibrations caused them to emerge as adults with reduced fat stores, a worker trait. This suggests that AD influences the larval developmental trajectory by inhibiting a physiological element that is necessary to trigger diapause, a gyne trait.

A brief review of machine vision in the context of automated wood identification systems

The need for accurate and rapid field identification of wood to combat illegal logging around the world is outpacing the ability to train personnel to perform this task. Despite increased interest in non-anatomical (DNA, spectroscopic, chemical) methods for wood identification, anatomical characteristics are the least labile data that can be extracted from solidwood products, independent of wood processing (sawing, drying, microbial attack). Wood identification using anatomical characteristics is thus still a viable approach to the wood identification problem, and automating the process of identification is an attractive and plausible solution. The undisputed increase of computer power and image acquisition capabilities, along with the decrease of associated costs, suggests that it is time to move toward non-human based automated wood identification systems and methods. This article briefly reviews the foundations of image acquisition and processing in machine vision systems and overviews how machine vision can be applied to wood identification.

Data-Driven Design Optimization for Composite Material Characterization

The main goal of the present paper is to demonstrate the value of design optimization beyond its use for structural shape determination in the realm of the constitutive characterization of anisotropic material systems such as polymer matrix composites with or without damage. The approaches discussed are based on the availability of massive experimental data representing the excitation and response behavior of specimens tested by automated mechatronic material testing systems capable of applying multiaxial loading. Material constitutive characterization is achieved by minimizing the difference between experimentally measured and analytically computed system responses as described by surface strain and strain energy density fields. Small and large strain formulations based on additive strain energy density decompositions are introduced and utilized for constructing the necessary objective functions and their subsequent minimization. Numerical examples based on both synthetic (for one-dimensional systems) and actual data (for realistic 3D material systems) demonstrate the successful application of design optimization for constitutive characterization.

Mechanical and time-dependent behavior of wood–plastic composites subjected to tension and compression

The thermoplastics within wood–plastic composites (WPCs) are known to experience significant time-dependent deformation or creep. In some formulations, creep deformation can be twice as much as the initial quasi-static strain in as little as 4 days. While extensive work has been done on the creep behavior of pure polymers, little information is available on the mechanical effects of mixing polymers with large amounts of wood-based or other bio-based fillers. As producers seek to develop structural WPC products that may be subjected to sustained loads, it is imperative that this creep behavior be understood. We characterized the quasi-static and time-dependent deformations of seven WPC formulations (primarily polypropylene, and polyethylene) in tension and compression. The quasi-static, mode-dependent response of the material to a linearly increasing strain was found to be well described by an exponential function coupled with a linear term. For most formulations, significant differences between the tension and the compression behaviors were not exhibited below 50% of the tensile capacity. The long-term creep response of the material was found to conform well to a time-dependent power-law (Findley, Shapery, etc.) at various stress levels for both loading modes.

First Industrial Strength Multi-Axial Robotic Testing Campaign for Composite Material Characterization

In this paper we are reporting on the first successful campaign of systematic, automated and massive multiaxial tests for composite material constitutive characterization. The 6 degrees of freedom system developed at the Naval Research Laboratory (NRL) called NRL66.3, was used for this task. This was the in-augural run that served as the validation of the proposed overall constitutive characterization methodology. It involved accomplishing performing 1152 tests in 12 business days reaching a peak throughput of 212 tests per day. We describe the context of the effort in terms of the reasoning and the actual methods behind it. Finally, we present representative experimental data and associated constitutive characterization results for representative loading paths.© 2012 ASME

Towards a Recursive Hexapod for the Multidimensional Mechanical Testing of Composites

Automated inverse methods for material constitutive characterization under multidimensional loading conditions has motivated the custom design, manufacturing and utilization of mechatronic loading machines. This present paper reports on the architecture of a mechatronic system capable of enforcing 6-DoF kinematic boundary conditions on deformable material specimens under testing, while at the same time measuring both the imposed kinematics and the corresponding reaction forces in a fully automated manner. This system has a recursive nature as it consists of a hexapod configuration that repeats itself six times. In addition to the architecture, we also present the historical evolution, and current status of its manufacturing implementation and the initial fielding of our system for composite material testing and characterization.Copyright

Predicting the Flexure Response of Wood-Plastic Composites from Uni-Axial and Shear Data Using a Finite-Element Model

AbstractWood-plastic composites (WPCs), commonly used in residential decks and railings, exhibit mechanical behavior that is bimodal, anisotropic, and nonlinear viscoelastic. They exhibit different stress-strain responses to tension and compression, both of which are nonlinear. Their mechanical properties vary with respect to extrusion direction, their deformation under sustained load is time-dependent (they experience creep), and the severity of creep is stress-dependent. Because of these complexities, it is beneficial to create a mechanics-based predictive model that will calculate the material’s response in situations that are too difficult or expensive to test experimentally. Such a model would also be valuable in designing and optimizing new structural shapes. Analysis and prediction of WPC members begins with the time-dependent characterization of the material’s axial and shear behaviors. The data must then be combined with a tool that can simulate mode-dependence, anisotropy, and nonlinear axial st...

Performance Analysis and Experimental Validation of the Direct Strain Imaging Method

Direct Strain Imaging accomplishes full field measurement of the strain tensor on the surface of a deforming body, by utilizing arbitrarily oriented engineering strain measurements originating from digital imaging. In this paper an evaluation of the method’s performance with respect to its operating parameter space is presented along with a preliminary validation based on actual experiments on composite material specimens under tension. It has been shown that the method exhibits excellent accuracy characteristics and outperforms methods based on displacement differentiation.Copyright

Preliminary Validation of Composite Material Constitutive Characterization

This paper is describing the preliminary results of an effort to validate a methodology developed for composite material constitutive characterization. This methodology involves using massive amounts of data produced from multiaxially tested coupons via a 6-DoF robotic system called NRL66.3 developed at the Naval Research Laboratory.

Composite Material Testing Data Reduction to Adjust for the Systematic 6-DoF Testing Machine Aberrations

This paper describes a data reduction methodology for eliminating the systematic aberrations introduced by the unwanted behavior of a multiaxial testing machine, into the massive amounts of experimental data collected from testing of composite material coupons. The machine in reference is a custom made 6-DoF system called NRL66.3 and developed at the NAval Research Laboratory, that consists of multiple sets of hexapod configurations essentially forming a recursive synthesis of multiple parallel mechanisms. Hexapod linkages, the grips, and other deformable parts of the machine absorb energy. This is manifested in an either reversible or irreversible manner, thus introducing a parasitic behavior that is undesirable from the perspective of our ultimate goal of the material constitutive characterization. The data reduction focuses both on the kinematic (pose of the grip) and the reaction (forces and moments) that are critical input quantities of the material characterization process. The kinematic response is reduced by exploitation of the kinematics of the dots used for full field measurements. A correction transformation is identified by solving an inverse problem that minimizes the known displacements at the grips as given by the full field measurements and those given by the machine’s displacement sensors. A Procrustes problem formalism was introduced to exploit a known material behavior tested by the testing machine. Consequently, a correction transformation was established and was applied on the load cell data of the machine in order to eliminate the spurious responses appearing in the force and moment data.Copyright