White and Dark Layer Analysis Using Response Surface Methodology

This paper presents a study of the influence of cutting conditions on the finished surface obtained after an hard turning process, in particular a case study is presented where AISI 52100 bearing steel is machined under different cutting conditions. An analysis carried out using Surface Response Methodology has been developed in order to study the influence of the main cutting parameters such as cutting speed, feed rate and workpiece initial hardness on white (WL) and dark layer (DL) thickness. The whole experimental campaign has been performed using a chamfered PCBN tool inserts without any cutting fluid. Results show an evident influence of cutting speed and feed rate on both white and dark layer thickness while less relevant is the contribute given from the workpiece hardness on defining WL and DL depth. Finally, a model to find the optimal process conditions to minimize white and dark layer thickness is developed.

Experimental Study on Microstructure Evolution in AISI D2 Steel Surface Grinding

The microstructure evolution of ground subsurface in AISI D2 steel surface grinding was investigated in this study. The effect of grinding parameters and grain size of wheels on white layer formation was presented. The surface integrity parameters of microstructure and microhardness were measured and analyzed. It was found that the white layer and dark layer may occur more easily when using finer grain size of wheel and white layer and dark layer may occur with the increase of grinding parameters, such as wheel rotation speed, workpiece speed and depth of cut.

Sub-decadal- to decadal-scale climate cyclicity during the Holsteinian interglacial (MIS 11) evidenced in annually laminated sediments

To unravel the short-term climate variability during Marine Isotope Stage (MIS) 11, which represents a close analogue to the Holocene with regard to orbital boundary conditions, we performed microfacies and time series analyses on a ~3200-yr-long record of annually laminated Holsteinian lake sediments from Dethlingen, northern Germany. These biogenic varves comprise two sub-layers: A light layer, which is controlled by spring/summer diatom blooms, and a dark layer consisting mainly of amorphous organic matter and fragmented diatom frustules deposited during autumn/winter. Time series analyses were performed on the thickness of the light and dark layers. Signals exceeding the 95 % and 99 % confidence levels occur at periods that are near-identical to those known from modern instrumental data and Holocene palaeoclimatic records. Spectral peaks at periods of 90, 25, and 10.5 yr are likely associated with the 88-, 22- and 11-yr solar cycles, respectively. This variability is mainly expressed in the light layer spectra, suggesting solar influence on the palaeoproductivity of the lake. Significant signals at periods between 3 and 5 yr and at ~6 yr are strongest expressed in the dark layer spectra and may reflect an influence of the El Niño-Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO) during autumn/winter. Our results suggest that solar forcing and ENSO/NAO-like variability influenced central European climate during MIS 11 similar to the present interglacial, thus demonstrating the comparability of the two interglacial periods at sub-decadal to decadal timescales.

A study of high Cu behavior on electrolytic Ni and electroless Ni pad finish

It has been used various pad finish materials to enhance the reliability of solder joint and Electroless Ni Immersion Gold (the following : ENIG) pad has been used more than others. This study is about reliability according to being used in commercial Electrolytic Ni pad and ENIG pad, and was observed behavior of various Cu contents. After reflow, the inter-metallic compound (IMC) between solder and pad is composed of Cu6Sn5 (Ni substituted) by using EDS, and in case of ENIG, between IMC and Ni layer was observed the dark layer (Ni3P layer). Additional, it could be controlled the thickness of dark layer according to Cu contents. Investigated the different fracture mode between electrolytic Ni and ENIG pad after drop shock test, in case of soft Ni, accelerated stress propagated along the interface between 1st IMC and 2nd IMC, and in case of ENIG pad, accelerated stress propagated along the weaken surface such as dark layer. The unstable interface exists through IMC, pad material and solder bulk by the lattice mismatch, so that the thermal and physical stress due to the continuous exterior impact is transferred to the IMC interface. Therefore, it is strongly requested to control solder morphology, IMC shape and thickness to improve the solder reliability.