Untersuchungen über die Holzeigenschaften von Douglasien aus linksrheinischen Anbaugebieten
The wood-properties of Douglas firs grown on various sites and under different growth conditions on the west-side of the Rhein in the districts Trier and Koblenz (mostly in the Eifel- and Hunsrück-hills) were investigated. Some of the test-trees were grown in pure stands, some in mixed stands between broadleaved species or spruces. Investigations comprehended year ring analysis, percentage of summerwood, thickness of branches, hardness, length of tracheids and wood density (based on volume when green and weight when ovendry). From several stems grown on a good site also the strength properties of wood were tested. For production of timber of high specific gravity and useful for deals and veneer an early limitation of diameter growth is desirable, however on better sites with abundant soil moisture supply is difficult to obtain. The best wood quality was found in densely stocked pure stands, while Douglas firs mixed in wide distance with broad-leaved species were rapidly grown, developed very big crowns with thick branches, conical trunks and broad annual rings. In the examined stands percentage of summer-wood was rather high. The average specific gravity value corresponded exactly with american second-growth stands of coast type. Test-trees from a fully stocked stand showed excellent stress properties, especially high values of bending strength, modulus of elasticity and shock resistance. The quality of the converted lumber cut from test-trees will be discussed in a following essay.
Impact of spacing and pruning on quantity, quality and economics of Douglas-fir sawn timber: scenario and sensitivity analysis
Controlling the long-term effect of management on the quantity and properties of individual boards is a fundamental challenge for silviculture. Within this basic study on Douglas-fir, we have investigated the sensitivity of the net present value (NPV) to three most common planting densities and a prominent pruning strategy. We therefore have applied an individual tree growth model, which represents intrinsic stem structure as a result of crown competition. The model extrapolated board strength development to the rotational age of 70 years, starting from real and comprehensive data recorded from experimental Douglas-fir plots at the age of 20 years. Total volume production increased from about 1600 m3 ha−1 for 1000 and 2000 trees ha−1 to 1800 m3 ha−1 for 4000 trees ha−1. The economic superiority of the lowest density stands increased considering the NPV at inflation-adjusted interest rates of 0%, 2% and 4%: Given an interest rate of 2% and no pruning, the NPV at 2000 was at about 50% of the one at 1000 trees ha−1. The NPV at 4000 trees ha−1 was even negative. Generally, artificial pruning was not effective. The revealed financial trade-off between growth and timber quality in young stands underlines the importance of silvicultural guidelines, which quantify the effect of management on yield per strength class and financial outcome.
Failure analysis for poor solderability of Au surface of PCB
Nonwetting is one of the common problems and is always rejected in electronic assemblies. ENIG pads of a PCBA exhibited nonwetting after lead-free reflow soldering. With the aid of stereomicroscope, SEM&EDS and XRF, a series of analysis was performed. And after visual inspection, surface and cross section analysis, thickness measurement and solderability test, it can be inferred that oxidation of plating surface was the main reason for nonwetting, and corrosion in Ni plating caused an adverse impact on solderalibity.