Process fluid as a technological system element of vibro-impact parts processing

Vibro-impact processing refers to finishing processing methods, which largely determine the operational part properties. It is shown that the parameter optimization of the vibro-impact processing is a very promising area of improving the part quality and reducing their manufacturing cost.One of the most important technological system elements is the process fluid. As a result of the priory information analysis, factors that determine the parameters of the vibro-impact processing were identified.Because of theoretical studies, the process fluid parameters and flushing mode influence degree on the process parameters and treated part quality indicators was determined. The process fluid is presented as a set of unit volumes that form an elastically deformable matrix. The necessary list of initial data for determining the maximum allowable process fluid amount in the mass load volume has been identified.The dependence for determining the minimum required process fluid volume is presented. A complex parameter that characterizes the change in the load mass volume in one oscillations cycle, together with the working chamber oscillation frequency and the process fluid fluidity, which determine both the fluid flow process nature (turbulent) and the flow rate inside the load mass is proposed. Based on the complex parameter, the load mass flushing speed is determined. It is shown that at this stage, the numerical value of the parameter can only be determined experimentally. Its theoretical definition is a promising area of further research.

Predicting productivity of timber loading operations: a literature review

Loading is considered a bottleneck of the forest harvesting system as it acts as a connection between primary transport and secondary transport (from roadside/ landing to mills or central yards). Any delay during the loading component can cause delay in the primary wood extraction and/ or secondary transportation. This article reviewed the current knowledge on loading productivity studies. Based on the results, the main variables impacting the loading productivity include log size, log lengths, load volume per truck, number of logs (or pieces) per truck and number of safety straps. The productivity of loading operations ranged from 3.4 m3/PMH0 in a manual loading to 168.9 m3/PMH0 using mechanised loaders. The results of this review can assist the academic and industrial users for predicting, controlling and managing the productivity of loading operations. 

Effect of kettlebell training on bone mineral density in two older adults with osteoporosis: a multiple-case study from the BELL trial

The purpose of this case study was to report clinically significant increases in bone mineral density (BMD) in a female and a male over 70 years of age with osteoporosis, following 16 weeks of hardstyle kettlebell training. Both case subjects were insufficiently active prior to participating in the BELL trial. Subjects trained five days a week accruing a large training load volume (calculated as kettlebell weight multiplied by repetitions performed) during structured group-based classes (74,872 kg and 110,132 kg, respectively). Regional dual-energy X-ray absorptiometry was used to assess BMD at the hip and lumbar spine. Increases in BMD of 12.7% and 5.9% at the femoral neck and lumbar spine (L2-L4) respectively were observed for the female, and 2.5% and 6.0% respectively for the male. Magnitude of change in BMD (g/cm2) at the lumbar spine was 2.0 and 1.9 times larger than the least significant change for the female and male respectively, and sufficient to advance the female subject's status from osteoporosis to osteopenia. Although these results do not show a definitive causal relationship between kettlebell training and increased BMD, further investigation of the effects of kettlebell training on BMD in older adults with osteoporosis and osteopenia is warranted.

Evaluation methods and objectives for neuromuscular and hemodynamic responses subsequent to different rest intervals in resistance training: a systematic review

Introduction: The training routine planned, and performed correctly results in exercises that, systematically organized, influence the levels of strength, and muscle hypertrophy. However, the magnitudes of these gains vary considerably. To optimize these gains, it is important to underst, and the interaction between training variables such as external load, volume, number of exercises, number of repetitions, duration of repetitions, the order of exercises, number of series, recovery interval between series, and the exercises, as well as the time under tension. The influence of the recovery interval on the response following exercise on neuromuscular components is very important. However, different objectives, and instruments are used to evaluate these responses. Objective: The purpose of this study is to conduct a systematic review of the assessment methods, and objectives for responses after different recovery intervals in strength training. METHODS: The present study is characterized by a systematic review study. Articles found in the following databases were considered for the systematic review: Scopus, PubMed / MEDLINE, Web of Science, Cochrane Library. The following descriptors, and their respective synonyms according to the terms MeSH were used in the databases, both singular, and plural: “Resistance Training”, “Rest Interval”, and “Bech Press”. As filters were used: a) species (humans), and type of study (original). Results: Seven studies were analyzed that met the established criteria. Conclusion: The studies presented have verified the influence of different recovery intervals on muscle, and hemodynamic responses. Evaluating image measurements such as ultrasound, and resonance, blood measurements such as GH, Testosterone, IGF-1, and Lactate, number of repetitions for performance, and fatigue, as well as heart rate, and blood pressure.

Incorporation of the effect of strain rate in Mie-Gruneisen equation of state for polyethylene

Volume change versus pressure is expressed through an equation of state (EOS) such as the well-known Mie-Gruneisen equation. Equation of state is an essential requirement to be defined for numerical simulation of high rate events such as impact. All EOSs have some coefficients which are identified by experiment and are usually considered constant and strain rate independent. In this study, the effect of strain rate on the coefficients of Mie-Gruneisen equation is obtained for polyethylene by experiment and numerical simulation. The low and high strain rate compression tests are conducted using Instron testing machine and Hopkinson bar, respectively. The load-displacement and load-volume change curves are obtained from the experiments. The strain rate dependent constants of Mie-Gruneisen equation of state are obtained through a combined experimental/numerical/optimization technique. The compression test is simulated using Ls-dyna hydrocode. The results show that the coefficient γ is not affected by strain rate but the coefficients C and S1 are severely strain rate dependent. The latter varies with strain rate in a linear fashion and the former varies cubically with strain rate.

Influence of stand and terrain characteristics on the productivity of the Timberjack 240b tractor in pure beech stands

This paper presents the results of research of the Timberjack 240b tractor equipped with a double-drum winch (work form 1 Tractor driver + 0 Assistant) in beech stand at an average elevation of 983.73 m. The research was conducted using the time and work study method, with the help of GIS technology in certain segments of research. The achieved working hours consist of 75.44% effective time and 24.56% delay time. The delay time coefficient is 1.33. In total, 47 transport cycles were realized, with 66 stopping points, an average of 1.41 per transport cycle. The average skidding distance was 221.19 m. In total, 363 logs (204.04 m3) were collected by 79 winches. The average load volume was 4.34 m3 and consisted of 5.43 pieces. Loaded tractor skidding time is strongly influenced by skidding distance and load volume in interaction with the longitudinal slope of skidding trails. To increase tractor productivity, it was concluded that the skidding roads should be built with the smallest longitudinal slope possible. Preferably, logs should be skidded downhill.

Reviewing productivity studies of skidders working in coniferous forests and plantations

Skidding is an important element of harvesting operations, which contributes to the extraction of wood. A skidder can be used in different types of harvesting operations, such as thinning, clear fell, native forest thinning or salvage work. The main goal of this article was to review the available stud-ies on productivity of skidding operations in coniferous forests/ plantations. Information on skid-der productivity was collected from publications and then was classified in three regions, including North America, Europe and the Southern Hemisphere. The parameters affecting machine productivity included machine type/ size, tree volume/ log volume/ load volume, average skidding distance and slope of the ground for each reported productivity. The average productivity reported in the published reports ranged from 9.3 m3/PMH to 78.0 m3/PMH. Detailed information and conclusions collected from various studies can be of use to forest academic and industry users to gain knowledge about vari-ations of skidder productivity in different regions and site/ operation conditions, which can be helpful for predicting, controlling and improving current levels of productivity. 

Multi-Product Forwarder-Based Timber Extraction

Accurate predictions in forest operations can be used towards effective planning, costing, and maximizing the productivity of machines in mechanised cut-to-length (CTL) harvesting. There is a general and substantial gap in forwarder productivity data available for pine sawtimber in South Africa at present, and as the number of product assortments being harvested increase there is a need for more work to quantify the effects of extracting products of different dimensions. The aim of this study was to calculate the time consumption and productivity of two models of Ponsse forwarders (15 t and 20 t capacity) to consider and compare the effects of multiple variables including machine capabilities, product assortment, load size, extraction distance and fuel consumption. Productivity averaged at 34.08 m3 per productive machine hour excluding delays longer than one minute (PMH1) for the smaller machine, and 55.94 m3/PMH1 for the larger machine. Productivity and average log volume were strongly positively correlated. Regression models were created for each machine where load volume and extraction distance were both significant factors for predicting productivity. Average fuel consumption of the smaller machine was 15.55 l/PMH1 and 0.47 l/m3, and 20.57 l/PMH1 and 0.43 l/m3 for the larger machine. The product with the largest volume was found to require the least fuel per m3. The models developed could aid in predicting system productivity and potentially carbon emissions under similar conditions in a South African context of industrial plantation forestry.