Search

In a free-state condition, deformable bodies (or compliant parts) have a significantly different shape than their nominal geometry (CAD model) due to gravity loads and residual stress. Typically, the dimensional metrology of such parts requires a particular approach where expensive and specialized jigs are needed to constrain and follow the component during inspection. This paper proposes a new method to fixtureless inspect deformable bodies by adapting the coherent point drift (CPD) algorithm. This new approach combines the optimization of the smoothness regularization parameters of the CPD powerful non-rigid registration method alongside the Thompson-Biweight statistical test as an identification method to distinguish profile and localization process manufacturing defects from a part's deformation. In other words, a new 'flexible' registration approach that meets the specifications of compliant parts is proposed. The CAD model is smoothly modified to fit the scanned part by minimizing two criteria that belong to deformable bodies. The first criterion is the conservation of the curvilinear distance (isometric transformation). That is to say, the condition that the stretch difference between the original CAD model and the modified one should be very small. The second criterion is the usual minimization of the Euclidean distance between the modified CAD model and its corresponding scanned part. Many case studies were performed on a typical industrial sheet metal which presented profile and localization defects. The estimated values of the defects, as well as their positions, are much closer to their reference ones in most cases, thus reflecting the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

An accurate approach of the instantaneous undeformed chip thickness is a key issue for analyzing milling process. The presented models for approximating instantaneous undeformed chip thickness are oversimplified and complex for use in academic and manufacture practice. In this paper, a new model for determining the undeformed chip thickness in milling process with higher accuracy is proposed. According to the true trochoid path of tool tooth, the true instantaneous undeformed chip thickness can be derived by solving the deduced transcendental equation. An iterational algorithm is used to approach the value in the transcendental equation with infinitesimal calculation error. Our main contributions include that the accurate positions of the geometric points of the undeformed chip profile with different level of width of cut are analyzed and derived, as well as the accurate undeformed chip thicknesses of the chip cross-section profile are approached by iterative algorithm. Case studies with different parameter combinations show that the new model has a higher accuracy compared with the presented models. With this innovative approach, a method of accurate prediction of the geometric profile and thickness of the undeformed chip profile in milling process is provided. [ABSTRACT FROM AUTHOR]

This paper presents a variational formulation of viscoplastic constitutive updates for porous elastoplastic materials. The material model combines von Mises plasticity with volumetric plastic expansion as induced, e.g., by the growth of voids and defects in metals. The finite deformation theory is based on the multiplicative decomposition of the deformation gradient and an internal variable formulation of continuum thermodynamics. By the use of logarithmic and exponential mappings the stress update algorithms are extended from small strains to finite deformations. Thus the time-discretized version of the porous-viscoplastic constitutive updates is described in a fully variational manner. The range of behavior predicted by the model and the performance of the variational update are demonstrated by its application to the forced expansion and fragmentation of U-6%Nb rings. [ABSTRACT FROM AUTHOR]