John P. Parmigiani

A Water Soluble Additive to Suppress Respirable Dust from Concrete-Cutting Chainsaws: A Case Study

Respirable dust is of particular concern in the construction industry because it contains crystalline silica. Respirable forms of silica are a severe health threat because they heighten the risk of numerous respirable diseases. Concrete cutting, a common work practice in the construction industry, is a major contributor to dust generation. No studies have been found that focus on the dust suppression of concrete-cutting chainsaws, presumably because, during normal operation water is supplied continuously and copiously to the dust generation points. However, there is a desire to better understand dust creation at low water flow rates. In this case study, a water-soluble surfactant additive was used in the chainsaws water supply. Cutting was performed on a free-standing concrete wall in a covered outdoor lab with a hand-held, gas-powered, concrete-cutting chainsaw. Air was sampled at the operators lapel, and around the concrete wall to simulate nearby personnel. Two additive concentrations were tested (2.0% and 0.2%), across a range of fluid flow rates (0.38–3.8 Lpm [0.1–1.0 gpm] at 0.38 Lpm [0.1 gpm] increments). Results indicate that when a lower concentration of additive is used exposure levels increase. However, all exposure levels, once adjusted for 3 hours of continuous cutting in an 8-hour work shift, are below the Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) of 5 mg/m3. Estimates were made using trend lines to predict the fluid flow rates that would cause respirable dust exposure to exceed both the OSHA PEL and the American Conference of Governmental Industrial Hygienists (ACGIH®) threshold limit value (TLV).

A Study of Chainsaw Kickback

Abstract Chainsaw kickback is a serious safety concern for both experienced and novice operators. A key to developing improved kickback control systems is a better understanding of saw motion during kickback and the development of improved methods for distinguishing kickback from normal saw operation. In this study, accelerometers and gyroscopes were mounted to a battery-powered electric chainsaw and to a midsize, gasoline-powered chainsaw, and data were collected during normal cutting and kickbacks. These sensors measured accelerations along the guide bar and perpendicular to the bar as well as rotational velocities toward the operators torso. Results from the battery-powered saw showed that accelerations during normal cutting and kickbacks had peak magnitudes of from ~2 to ~6 g and from ~6 to ~8 g, respectively, and that rotational velocities typically reached over 600°/s during a kickback. Analysis of these results showed that the gyroscope alone, using a threshold value of 300°/s, was effective in di...

Autonomous Unmanned Aerial Vehicle System for Controlling Pest Bird Population in Vineyards

Pest birds have long been a significant source of crop loss for grape growers, especially during the critical weeks leading up to harvest when grape sugar levels are high. In Oregon’s Willamette Valley, vineyards have seen a marked increase in crop loss in the last few years despite widespread use of intrusive gas cannons/shotguns and expensive netting systems. In order to deter this pest bird population, we have created an Unmanned Aerial Vehicle (UAV) package capable of autonomous flight, which incorporates common pest bird scare tactics into this dynamic platform. The system has been designed to launch, complete its mission waypoints, and land completely under autonomous control. By using this autonomous guidance system, we are able to employ visual, auditory, and predator mimicry pest bird control techniques in such a way as to discourage habituation. While radio controlled UAVs have been used for bird control in airport settings for many years, these systems require a trained operator to constantly guide the aircraft. The autonomous UAV system was designed for operation by an existing vineyard employee with minimal training. To capture widely accepted pest bird control techniques and management culture of Willamette Valley vineyards and gain information for design, implementation, and industry acceptance of this UAV project, we surveyed the owners of 225 local vineyards. Survey results indicated that vineyard owners are open to implementing innovative pest bird control methods that do not affect the terroir of their vineyards and that could replace the use of netting, which they do not view favorably despite its being the most effective pest bird control method to date. Results also indicated that pest birds are most damaging to a vineyard’s perimeter and that many vineyards employ someone to patrol this perimeter with a shotgun loaded with cracker shells. The UAV system is able to traverse the airspace above this perimeter without interfering with neighboring homes or beneficial predators in the area. By using proven pest bird control methods in an autonomous UAV system, we designed a device that brings an innovative solution to vineyard owners.Copyright

Effects of Finite Element Damage Modeling Parameters in Carbon Fiber Panels Under Mode III Loading

Modeling the progression of damage is required to fully describe the behavior of advanced composite materials in engineering applications. However, damage progression can be complex and is often difficult to determine. Errors in analyses can arise due to uncertainties in the material parameters associated with damage progression models. The commercial software Abaqus uses the Hashin damage criterion that consists of six strength based damage initiation material inputs and four energy based damage propagation inputs for composite lamina. The initiation inputs consist of the tensile and compressive strengths parallel and perpendicular to the fiber direction, longitudinal shear strength, and transverse shear strength. The damage propagation properties consist of the fracture-energies that define the stress-displacement relationship for tension and compression of the fibers and the matrix. To create an accurate finite element model, it is important to understand the effects of the material properties on the outputs of the analysis. The research presented in this study will determine the effect of the ten damage properties under a specific loading case using an Abaqus finite element model, with a focus on determining when the four damage progression properties have a significant effect. Edge-notched panels under mode III loading with 20 and 40 ply layups consisting of 30% zero degree plies were considered in the study. The explicit solver in Abaqus was used for the panel analysis. To evaluate the effects of the properties, fractional factorial sensitivity studies were used. Fractional factorials allow for a broad screening of several factors at relatively small computational cost. The factorial design used the ten Abaqus Hashin properties as factors at levels of ±50% from their nominal values. The maximum load the panel experienced was used as the metric for comparison. The effects were then calculated, weighted to the sum of all effects, and plotted to compare each factor. For both the 20 and 40 ply panels, the tensile strength in the direction of the fibers was shown to have the largest effect. The 20 ply panel showed a very small effect of the fracture energy of the fiber in tension, while the 40 ply panel showed a greater effect of this parameter. This is due to damage propagation mainly occurring after max load for thinner panels. Thicker panels are able to transfer load to more plies as damage occurs and the material softens. This allows the panel to carry an increased load after initial damage and through damage progression. Therefore the damage propagation has more of an effect on max load for the 40 ply panels. This principle is illustrated by differences in the experimental load displacement curve shapes of the 20 and 40 ply panels. In addition, the analysis showed the thicker panels exhibited more damage at the maximum load. These results illustrate where in the mode III loading case the damage progression properties have a major effect. This can be used to inform future analysis and inform further research into measuring the damage progression of composite materials.Copyright

Effective Finite Element Modeling of Mode III Failure in Composites

The ever increasing use of composite materials in today’s society has created a drastic demand for better modeling of their behavior. The difficulty arises in that many modern composite structures are unique in shape and are exposed to a variety of loading situations. More specifically, loading scenarios which cause out-of-plane shear (Mode III) or mixed mode (Mode I + Mode II + Mode III) failure are of greatest challenge to model. This study investigates the capabilities of Simulation Composite Analysis (SCA), a composites software by Autodesk, in modeling failure in notched carbon-fiber composite panels loaded in Mode III. SCA was used with the finite element modeling software Abaqus/Standard (Dassault Systemes) to model six different laminate stacking sequences. Three of the layups featured 40 plies through the thickness and the other three had 20 plies, with each containing either 10, 30, or 50 percent zero degree plies. The modeled panels were displaced as to create for a Mode III loading condition and the resulting maximum loads, load-displacement plots, and damage propagation outputs were compared to experimental results. It was found that SCA can determine the maximum failure load of the panels with an average of 11.6 percent deviation from experimental values. For one laminate stacking sequence in particular, the software determined maximum loads that deviated less than 1 percent from the experimental data. The load-displacement plots showed good correlations with experimental data in the linear region; however, the load-displacement behavior after damage was well modeled for only certain layups. The damage propagation paths for all the panel models were similar to the experimental panels in general, though self-similar damage propagation was not captured by the FEA models. Overall, Mode III failure in the notched carbon fiber panels was satisfactorily modeled for maximum load, but continued development is needed for predicting damage propagation paths. Modeling Mode III failure in composites is a difficult task; therefore, determining accurate methods in which to model such failure will be a substantial benefit to the composites engineering community. If low cost computer models can be established which accurately capture material damage and failure, the need for expensive and time-intensive experiments may be greatly reduced.Copyright

Mesh Selection for Progressive Failure Modeling of Carbon Fiber Panels in Mode III Shear Using an Explicit Finite Element Solver

Modeling progressive failure of composite materials can be a challenging task. It is further complicated by mesh dependency of finite element solvers when implementing the Hashin criterion. As one continues to refine the mesh, the finite element analysis (FEA) continues to yield varying solutions; hence there is no converged solution for continuous mesh refinement. This is due to mesh dependency when modeling strain softening. The FEA package Abaqus attempts to mitigate this but the issue is not eliminated.Methods that address mesh dependency include experimental validation and numerical analysis. Experimental validation tailors the mesh to match a specific result. This mesh would then be applicable to other configurations with the same geometry and loading; however, experimental validation with increasingly complex parts for FEA is costly and time consuming. Numerical approaches to mesh selection do not require experimental validation; however, these methods may be computationally expensive depending on the analysis. A mesh selection strategy that does not require experimental validation, while computationally efficient, should be implemented for design purposes.This study investigates a mesh selection strategy based on a converged elastic solution; the coarsest mesh that converges to a solution in the linear-elastic portion of the material response is chosen for analysis. Previous studies using an implicit solver yielded good results for out-of-plane loading conditions; however this procedure has not been implemented for explicit solvers. In this study, an investigation was conducted to determine the appropriate mesh to model progressive damage for notched, carbon fiber composite panels in out-of-plane shear (mode III) using an explicit solver in Abaqus/Explicit. This study analyzed 20 ply thick panels and considered three stacking sequences: 10%, 30%, and 50% zero degree plies. The procedure initially disabled damage and identified the coarsest mesh that approached a converged elastic solution. Using this mesh, damage was enabled and the models were run with loading proceeding through damage initiation until failure. The panels’ material response were extracted from the finite element (FE) model and filtered in order to determine their maximum load-carrying ability. The FE predicted maximum loads were then compared to corresponding experimental data in order to validate the mesh selection procedure. This process is not limited to out-of-plane shear; the potential for this mesh selection method would allow for progressive failure simulation to be more applicable in the design process of composite structures instead of post-damage analysis.Copyright

Optimization Device for Grinding Media Performance Parameters

The investment casting industry relies heavily on the use of grinding media during manufacturing. Typically, grinding media, when used in this application, have very short effective lifetimes. Determining the optimum life of grinding media is a key cost-containment and manufacturing-efficiency issue. However, current methods for determining optimum life as well as evaluating new grinding media products and optimum operating parameters are highly subjective and often is a matter of operator opinion. This subjectivity can lead to the premature retirement or overuse of grinding media, increasing cost and decreasing efficiency. A means of objectively and efficiently evaluating grinding media for optimum life and operating conditions, as well as evaluating new grinding-media products is needed. The approach taken in this work is to create a relatively low-cost test apparatus that uses grinding equipment, media, and specimens typically seen in the casting industry and measures key parameters. Also, the apparatus produces the fundamental motions and application forces typical of human operators. The resulting apparatus simultaneously moves a specimen in three orthogonal directions while applying a user-defined grinding force. Applied force, electric power input, grinding-motor rotational speed, test-specimen surface temperature and material removal are recorded. All operations of the device are autonomously performed through LabVIEW. The apparatus was constructed using standard commercial products for less than

Cutting performance comparison of low-kickback saw chain

15,000. Data comparing applied load versus material removal rate, surface temperature, and total material removed can be collected for different materials and grinding media. The device has been used to grind inconel specimens subjected to 10 to 70 pounds (45–312 N) of contact force corresponding to material removal rates of 0.26 to 5.26 grams/s at temperature changes of 90 to 210 degrees Fahrenheit (32.2–98.9 degrees Celsius). This data was used to determine a correlation between changes in performance parameters and a drop in material removal rate, total material removed, and belt life. No significant difference was found between the material removal rate of saw-cut and flame-cut Inconel specimens, dispelling a commonly held belief. Knowing key parameters that identify the effective lifetime of grinding media is significant to the casting industry. Methods described in this paper can be used to optimize grinding media life and determine optimum operating parameters.Copyright

Effects of material property variation in composite panels

ABSTRACT Kickback is the leading cause of the most severe and traumatic chainsaw-related injuries. As a result, safety standards require chainsaw manufacturers to produce low-kickback saw chain. In order to understand the tradeoffs in current state-of-the-art saw chain, a comparison study was conducted on a custom test apparatus using four different saw chains, all with the same cutter geometry but different low-kickback chain features. Two modes of cutting were studied: nose-clear down bucking and boring. Cutting performance for boring with a chainsaw has not been studied previously. Regression modeling was used to generate cutting force and cutting efficiency trend lines for each of the different saw chains and cutting modes. In nose-clear down bucking, it was found that operator effort and cutting efficiency of a low-kickback chain with bumper drive links was of near-equal performance to that of a non-low-kickback chain (having no low-kickback features). In boring, all types of low-kickback saw chain elements required markedly higher operator effort and had lower cutting efficiency that of non-low-kickback saw chain. Furthermore, a substantial difference in cutting forces was found between differing designs of bumper drive link elements in both nose-clear down bucking and boring, highlighting the importance of proper bumper link geometry. Using these results and considering that the boring mode of operation is for experienced users, the casual chainsaw operator should always prioritize safety by using a low-kickback saw chain while professional users should select the chain that best suits their current cutting needs.

Mode III Loading of Composite Panels

Purpose The purpose of this paper is to determine which of the ten material properties of the Hashin progressive damage model significantly affect the maximum load-carrying ability of center-notched carbon fiber panels under in-plane tension and out-of-plane bending. Design/methodology/approach The approach used is to calculate the maximum load using a finite element model for a range of material property values as specified by a fraction factorial design. The finite element model used has been experimentally validated in prior work. Findings Results showed that for the laminates considered, at most three and as few as one of the ten Hashin material properties significantly affected the magnitude of the maximum load. Practical implications While the results of this paper only specifically apply to the laminates included in the study, the results suggest that, in general, only a small number of the Hashin material properties affect laminate load-carrying ability. Originality/value Knowing which properties are significant is of value in selecting materials to optimize performance and also in determining which properties need to be known to a high accuracy.