Vehicle/machine design and evaluation

Forest Road Network and Transportation Engineering – State and Perspectives

volume: 38, issue: 2

Trailer Overturning during Wood Transportation: an Experimental Investigation of Effects of Trailer Joint Point and Frame Structure

volume: 39, issue: 1

Trailers may increase the risk of tractor overturn during wood transportation in dangerous
conditions. In this work, tests were carried to simulate a trailer rollover using three two wheel
tractors and a crawler tractor and three trailers (two single-axle and one two-axle), all of their
combinations moving downhill along the path on a short dirt road. The trailers were always
loaded with the same load of logs cut at a length of about 1.5 m and put transversely to the
longitudinal axis of the trailer. During each test, the following parameters were measured: the
lateral dragging of the rear wheels/crawler of the tractor, the ground detachment of the rear
upstream wheel/crawler and both the longitudinal and transversal strains (released over the
tractor hooking system) produced by the trailer overturn. The study highlighted that the biaxle
trailer structure with a turntable steering had the best performances compared to the
single-axle in terms of safety during trailer overturning. Independently of the trailer type
considered in this work, a tied load is more dangerous than a load restrained only by steel
struts, because during the overturn the load forms a single unit with the trailer mass, which
increases the transversal and longitudinal strain.

Determination of Service Life of Sintered Powder Metallurgy Gears in Regard to Tooth Bending Fatigue

volume: 39, issue: 1

The aim of this study is to check the possibility of replacing the pinion gear made of structural
steel with the one made of sintered material. The pinion is part of the gear pair mounted
in front of the gearbox of the skidder Ecotrac 55V to increase the speed and lower torque. In
larger series, powder metallurgy (PM) gears are used as a cost-effective alternative for wrought
metal gears in a number of industries including the one producing forest products. The present
paper discusses the computational and experimental approach for determining the service
life of sintered PM gears in regard to tooth bending fatigue. The proposed computational
model is based on the stress-life approach, where the stress field in a gear tooth root is determined
numerically using finite element method. The needed material data have been taken
from the authors’ previous work. Due to the scattering nature of fatigue, the statistic approach
has also been considered by presentation of computational results. The experimental procedure
was done on a custom made back-to-back gear testing rig. The comparison between computational
and experimental results has shown that the proposed computational approach is an
appropriate calculation method for estimating the service life of sintered gears regarding tooth
root strength. Namely, it has been shown that, in case of proper heat treatment of tested gears,
tooth breakage occurred in the interval with 95% probability of failure, which has been determined
using the proposed computational model.

A Mobile Hydraulic Winch for Use in Small-Scale Forestry

volume: 39, issue: 2

Winches have recently been used to extract timber from forests. Winches are often components
of tractors, but tractors cannot be used on difficult terrain and are generally too expensive for
small forest owners. The current study considers the use of an experimental winch for the
extraction of timber from small plots with difficult terrain. The mobile hydraulic winch used
in this study weighs 50 kg and has a pulling force of up to 53 kN, a 12 V motor, and a 64x224 mm
drum. The associated power unit is a gasoline, single-cylinder, four-stroke, air-cooled KIPOR
KG 390D (400D), 389 cm3 engine, with 7.7 kW of power, and a torque of 22.6 Nm at 2500 rpm.
The engine powers a high-pressure oil pump with an output pressure of 3 MPa and a flow rate
of 60 litres per minute. The input torque of the pump shaft is 25 Nm at 3000 rpm. The hydraulic
winch can be fixed to tree trunks, stumps, or wooden pegs by lashings. The winch was
tested at three locations with different assortments of wood. The results showed that the experimental
winch was practical for timber extraction and that <250 kN of force was needed
for successful extraction. At the test sites, the expense of lumber removal was on average 140%
greater with the winch than with a horse but the advantage of the hydraulic winch is high
pulling force. Because of its small size and low weight, the unit can be easily handled by two
workers, easily moved at short distances in small plots with rough terrain, and easily transported
among plots. With a one-man crew, the percentage of direct costs represented by wages
dropped to 56%, and the percentage represented by fuel increased to 40%.

Effects of Steel Flexible Tracks on Forwarder Peak Load Distribution: Results from a Prototype Load Test Platform

volume: 40, issue: 1

Steel flexible tracks (SFT) are regularly installed on bogie axles of forwarders to improve traction
and extend trafficability by increasing the contact area between machines and operating surface.
The study quantified dynamic peak loads exerted by a forwarder driving either on wheels or
using additional SFT on its rear bogie axle. To examine load distribution of a full-scale forwarder,
a load test platform was designed and constructed. Three scenarios were tested with the
forwarder unloaded and loaded to quantify load distribution between wheels driven directly over
the steel load test platform (Scenario 1) and SFT when either driven directly over the steel load
test platform (Scenario 2) or when driven over a 20 cm layer of sand placed over the platform
(Scenario 3). The platform proved to be an appropriate measuring device for full-scale tests.
Results indicate that, when operated on the sand layer, SFT (installed on the forwarder’s rear
unloaded axle) decreased dynamic peak loads by about 30% compared to wheels. The use of SFT
on bogie axles of forest machines is recommended to lower soil disturbances, especially through
a reduction of peak loads often responsible for negatively altering soil physical properties.

Development of a Sensorized Timber Processor Head Prototype – Part 1: Sensors Description and Hardware Integration

volume: 40, issue: 1

Forest operations are in constant development to provide increasingly higher standards of
economic and environmental sustainability. The latest innovation trends are concentrated in
the generation, storage and management of data related to the harvesting process, timber
products and logistics operations. Current technologies provide productivity and position, but
only physical parameters are made available for timber products. The possibility of providing
a comprehensive quality evaluation of roundwood early in the supply chain and linking the
information to each log provides a new tool for optimization of the whole forest-timber supply
chain. Current in-field methods for grading logs are based on visual rating scales, which are
subjective, operator-dependent and time-consuming. As an alternative, a sensorized processor
head was developed, featuring the following sensors: near infrared (NIR) spectrometer and
hyperspectral cameras to identify surface defects, stress wave and time of flight sensors to
estimate timber density, hydraulic flow sensor to estimate cross-cutting resistance and delimbing
sensors to estimate branches number and approximate position. The prototype also deployed
an RFID UHF system, which allowed the identification of the incoming tree and individually
marked each log, relating the quality parameters recorded to the physical item and
tracing it along the supply chain. The tested sensors were installed and designed to be independent,
nevertheless, their integrated use provides a comprehensive evaluation of timber
quality. This paper presents the technical solutions adopted, the main hindrances found and
some preliminary results of the operative prototype as tested in laboratory and in forest operational

A Plackett-Burman Design to Optimize Wood Chipper Settings

volume: 40, issue: 1

The wood-chipping process is affected by several factors, notably chipper settings and wood
characteristics. It is often difficult to test all of these factors in a full factorial experimental
plan, due to the large number of trials required. On the other hand, a screening design of the
experiment makes it possible to manage a large number of variables in a small number of trials.
Hence, this approach is used to test six factors, in order to optimize the productivity and
chip quality of a drum wood-chipper. These factors are: feeding speed, screen size, PTO-speed,
wood species, wood moisture content, and wood diameter. Productivity was significantly affected
by screen size, while chip quality was related to feeding speed, screen size, PTO-speed,
and wood species. The results suggest that the optimal configuration can be achieved by adjusting
feeding speed, the PTO-speed, and the wood species, as these settings maximize chip
quality. Screen size requires further analysis, as larger sizes increase productivity but reduce
quality, while the opposite is true for smaller sizes. Thus, the optimal screen size requires a
consideration of costs and benefits that may change according to the retail price of premium
and regular wood chips, and production costs.


Web of Science Impact factor (2017): 1.714
Five-years impact factor: 1.775
Next issue: January 2019

Subject area

Agricultural and Biological Sciences