Waviness Defects Research Articles

On Planing Machine Engineering Characteristics and Machined Timber Surface Quality

Rotary machined timber surfaces exhibit small waves orthogonal to the timber feed direction resulting from the intermittent engagement of the cutting tool with the timber. These surface waves are typically less than five micrometres in height and when regularly spaced at 1 mm width characterize a good quality machined surface. Variations in the regularity of these surface waves are considered as surface defects. Machined timber surfaces produced by planing and moulding machines are a typical case. These surfaces will often exhibit waviness defects caused by inaccurate contact between the tool tip and the timber being cut. There are a number of different vibration sources on these machines. The primary cause of surface waviness defects has been found to be forced vibration, although inaccurate cutter servicing and relocation are also factors. The work presented in this paper concentrates on phenomena caused primarily by forced structural vibration. Systematic engineering and wood machining investigations are applied to a special purpose instrumented test rig so that correlation between vibration data and observed waviness defects can be established. The surface assessment of machined timber is carried out using a special purpose contact based surface tracing instrument. The engineering design and manufacturing influences that lead to unacceptable surface waviness variation effects are discussed.

Inspection of wood surface waviness defects using the light sectioning method

Surface waviness variations are a major type of defect on planed wood products. A number of methods have been investigated for the inspection of waviness defects on wood surfaces. This paper describes a new implementation of the light sectioning method with the latest structured lighting and machine vision techniques for this purpose. As a reference, a laser profilometer is used. The data from the light sectioning method and from the profilometer are highly correlated.

Localized Fiber Waviness and Implications for Failure in Unidirectional Composites

Finite element models with wavy material-orientation are used to represent periodic wavy fiber defects in composites. The homogenized material parameters in material coordinates (straight fiber properties) are determined originally by micromechanics modeling at the constituent level based on hexagonal fiber packing. To study the effects of local waviness, wavy material-orientation regions of material with different amplitude/wavelength ratios are embedded within regions of straight fiber material. A failure study has been performed for various types of localized fiber waviness. The modeling approach provides a systematic procedure to investigate the effects of fiber waviness defects on properties of unidirectional fiber composites.

Microbuckling elastic modelling approach of a single carbon fibre embedded in an epoxy matrix

Carbon fibre alignment defect inside of an epoxy matrix is examined by the use of microscopy and video recording. The initiation and the growth of a fibre waviness defect was monitored during the cure of the matrix. The observations established that fibre defect appears during the hot stage of the epoxy matrix thermosetting reaction. The objective is to evaluate the possibility of a fibre microbuckling mechanism to explain the observations. A first elastic microbuckling model is proposed. Analytical expressions of the necessary elastic load for the appearance of a fibre buckling instability and its associated wavelength are established. The compressive load applied onto the fibre has been evaluated by using finite elements calculations based on mechanical characteristics of the materials. Comparison between the critical microbuckling load and the applied load onto the carbon fibre during the cure is in coherence with the observations. The associated wavelength is discussed.

Wavy growth and related defects in strain-balanced multi-quantum wells for photovoltaic devices

Transmission electron microscopy, high resolution X-ray diffraction, cathodoluminescence were performed on strain balanced InGaAs based multi-quantum wells (MQWs) to be used as active layers in thermophotovoltaic devices operating at around 2 µm. The epitaxial growth front in the MQWs is flat up to a certain thickness where a change in the growth mode generates MQW waviness propagating vertically through the structure with increasing amplitude. The local stress concentration in the MQW regions exhibiting significant local rippling results in the formation of clusters of extended defects whose properties vary according to the strain and the growth temperature conditions of the structures. Experimentally it has been found that the wavy growth onset occurs once a threshold value of the elastic energy density is achieved. The well/barrier thickness ratio were changed in order to minimize this threshold energy and thus to retain good material quality even at the longer wavelength. Forty repetitions defect free MQWs, emitting at 1.96 µm at room temperature were successfully grown in this way.

Waves on wood

The rotary machining process as applied to timber is introduced and compared with the milling and grinding of metals. The emphasis of this work is on the waviness surface quality of the machined timber and initially focuses on a review of the techniques applied to improve surface quality at higher workpiece feed velocities—typically 120 m/min. The main work concentrates on mathematical and computer-based modelling of surface waviness defects generated by two classical woodworking machine engineering science phenomena, caused primarily by forced structural vibration. Surface assessment of machined timber is discussed, with results from contact and non-contact methods highlighted. The causes of surface waviness defects are presented and possible solutions are outlined.

Load transmission by elastic, elasto-plastic or fully plastic deformation of rough interface asperities

The normal contact between two nominally flat, parallel rough surfaces is analysed on the microgeometric scale from a theoretical point of view. The microgeometry is described using a probabilistic model based on the quantification of the variability in the summit altitude and the asperity radius. This model takes for its basic data six standardised parameters for roughness and waviness defects measured on both surfaces in contact. For a given separation between two surfaces, this model allows us to determine the number of asperities in contact and their respective indentations. For each asperity in contact, realistic indentation laws are developed taking into account either elastic, elasto-plastic or plastic deformation. The continuous sum of the loads at each asperity gives the global load at the contact and the force transmitted through elastic, elasto-plastic or fully plastic deformed asperities. The theoretical analysis of classical surfaces possessing various mechanical characteristics confirms the combined influence of microgeometry (roughness and waviness parameters) and mechanical characteristics (Young's modulus, Poisson's ratio and yield stress) on load transmission. The association of these parameters into a classical index for plasticity confirms previous predictions. The last necessary parameter is the normal load applied through the contact. This parameter does not appear in previous theories for the plasticity index but can drastically change the degree of plasticity in the contact. The main contribution of our research consists in the quantification of the proportion of plastification in the contact at a given normal load.

Simulation of the Influence of Manufacturing Quality on Reliability of Vias

Techniques based on physics-of-failure principles are fairly well established for mechanical design of electronic packages. This paper provides an example where such techniques can also be exploited to develop guidelines for assessment of manufacturing quality and its impact on reliability. As a case study, this study examines the influence of plating waviness in vias and Plated Through Holes (PTH), on reliability during solder reflow cycles and during subsequent operational thermal cycling. The stress analysis is performed with elastic-plastic finite element models which are seeded with various levels of plating waviness defects. Sensitivity analysis is done with factorial parametric simulation studies based on Design of Experiment (DOE) methods. Buckling and fatigue failure models are used to establish inspection criteria for acceptable thresholds of plating waviness.