Optical methods that give displacement or strain fields are now widely used in experimental mechanics. Some of the methods can only measure in-plane displacements/strains on planar specimens and some of them can give both in-plane and out-of-plane displacement/strain fields on any kind of specimen (planar or not). In the present paper, the stereovision technique that uses two cameras to measure 3-D displacement/strain fields on any 3-D object is presented. Additionally, a quite inclusive list of references on applications of stereovision (and 3-D DIC) to experimental mechanics is given at the end of the paper.

3-D computer vision in experimental mechanics

Curved tubes are widely used on autobody to suffer the transverse bending loads. This paper studies the energy absorption performance of curved tubes under transverse bending load. Firstly, three-point-bending and fully clamped bending experiments are conducted for three kinds of curved tubes with different radii. It is found that the curvature has a significant impact on the energy absorption effect under the fully clamped condition. However, the influence is limited and it will be easily ignored in the three-point-bending condition. Under fully clamped condition, tubes with large radii have three-plastic-hinges, and curved tubes with small radius have five-plastic-hinges. Due to the participation of axial force, the energy absorption of the curved tubes under fully clamped condition is 2.8–4.1 times that of the three-point-bending condition. Subsequently, FE models of curved tubes with different radii are established to analyze the effect of curvature on the deformation mechanism and energy absorption. It is found that whether the shortening of the plastic hinges can meet the requirements of geometric compatibility determines the deformation modes of curved tubes. The influence of loading (loading direction) and geometric (cross-section and thickness) factors are also discussed. Finally, a theoretical model of curved tubes with three-plastic-hinges mode is proposed to predict the energy absorption performance. 

Energy absorption performance of fully clamped curved tubes under transverse loading

Mechanical tests are used to determine a material’s behaviour under certain conditions of stress. Computer Vision Systems have been used since the 1980s in mechanical tests, with techniques evolving in order to accommodate modern needs. This paper has the purpose of reviewing research that combines Computer Vision Systems and Mechanical Tests, analysing the main steps for better results from such application.

A Review on Computer Vision Applied to Mechanical Tests in Search for Better Accuracy

The application of composite materials in vehicle thin-walled structure has attracted more and more interest by carmakers. This study aimed to investigate into the dynamic impact responses of the carbon fiber reinforced plastic (CFRP) header rail subjected to the vertical (Z-direction) and horizontal direction (X-direction) loading. The lightweight CFRP header rail was first fabricated using the wet compression molding process, special fixtures were designed and prepared for drop weight impact tests. The failure modes, force responses, energy absorption characteristics and the structural responses to different directional loads were compared. The global peak forces in X-directional tests were higher than those in Z-directional counterpart, but the energy absorption ratios were lower. It is shown that the impact performance of the specimens under Z-directional impact was better than under X-directional impact with same loading magnitude. The finite element (FE) models were then established in both impact directions for exploring the failure mechanisms. The simulated impact process, force–displacement curves and failure modes were found to be consistent with the experimental counterparts. After validation, damaged and weak areas of the specimen could be identified from the simulations, and the models could effectively predict the global peak force and energy absorption ratio. • Dynamic responses of CFRP header rail were investigated under vertical and horizontal impact. • The impact performance of the specimen was better under vertical impact than horizontal impact. • Failure modes and main contributors to energy absorption between different tests were compared. • Damaged and weak areas of the specimen were identified from the FE simulations. 

Experimental and numerical investigation into the dynamic impact responses of CFRP header rail

This paper presents an experiment-based synthetic structural analysis method that combines digital image processing (DIP) and the particle difference method (PDM), which is a strong form-based meshfree method. The proposed method uses images to determine the displacement of deformed specimens, interpolates the displacement onto nodes of the PDM model without meshes or grids, and calculates the kinematic variables. Furthermore, the pixel extraction method for the target area and the method of setting the region of interest for expediting DIP were used during the synthetic structural analysis. A method for effectively expanding the number of tracking points and an improved method for labeling tracking points are also presented. To verify the performance of the analysis, the experimental and numerical analysis results of a three-point bending test on a rubber beam were compared in terms of various mechanical variables as well as with the PDM results of a simulated bending test. It was found that tracking point expansion and adjusting the radius of the domain of influence are advantageous for performing an accurate calculation without losing computational efficiency. It was demonstrated that the synthetic structural analysis effectively overcomes the shortcomings of the conventional experiments and the limitations of pure simulations.

Experiment-Based Synthetic Structural Analysis Combining Digital Image Processing and a Strong Form Meshfree Method

The demand for new structural concept design of automotive parts has grown with weight reduction and improvement of crash safety in automotive industry. In this study, the established local patchwork hot stamping technology was used in structural design of hot-stamped automotive parts and expected to obtain maximum lightweight efficiency while maintaining crash performance by using local patchwork blanks instead of conventional reinforcement. Firstly, the technical feasibility of this technology was verified in an experimental method, and an optimization method was proposed to determine the optimal position and shape of local patchwork blanks. Then it was used for the improvements of two parts as examples, a top-hat channel created based on a conventional B pillar cross section and a B pillar. Finite element (FE) analysis models of these two parts were established based on the deformation of B pillar during full vehicle side impact and validated through experiments. It was confirmed that both the top-hat channel and the B pillar optimized have the same crashworthiness but became lighter compared to the original parts with reinforcement. Furthermore, the effects of local patchwork blank thickness, material strength and outer thickness on the optimal position and shape of local patchwork blanks and lightweight efficiency were investigated. Finally, the effectiveness of a hot-stamped B pillar with local patchwork blanks was verified through full vehicle side impact simulations. It can be concluded that the established local patchwork hot stamping technology and the proposed optimization method can be used as a dependable tool to design and manufacture hot-stamped parts with local patchwork blanks.

Design optimization and application of hot-stamped B pillar with local patchwork blanks

PROBLEM TO BE SOLVED: To provide a method for manufacturing a press-molded product for which a cost can be reduced and also a space can be saved by simplification of a metal mold structureSOLUTION: A method for manufacturing a press-molded product comprises: a process of locating a flat plate member 10 between a first metal mold 11 and a second metal mold 12; and a process of pressing the flat plate member 10 by causing a first press part 14A and a second press part 15A to approach each other In the process of locating the flat plate member 10, the flat plate member 10 is located so that a first principal surface 10C and a second principal surface 10D are along a vertical direction In the pressing process, the first press part 14A and the second press part 15A are caused to approach each other in the vertical direction, thereby pressing the flat plate member 10 in the vertical direction Further, in the pressing process, a part of material of the flat plate member 10 in the vertical direction is made to flow into a thickening formation part 16 formed on a first opposite surface 11A, thereby forming a thick portion on the flat plate member 10SELECTED DRAWING: Figure 3

Method for manufacturing press-molded product and press-molding device

This paper studies a method for evaluating the stress triaxiality and the fracture strains of thin steel plates which are used for an automobile body frame. Three-dimensional displacements and strains on the surface of the thin steel plates are measured using a stereovision. In particular, to measure the through-thickness deformation of the steel plates, the measurements are performed from the both sides of the steel plates. Based on the strain incremental theory, the stress triaxiality is evaluated from the measured strains considering the variation of the thickness of the steel plates. The effectiveness of the proposed procedure is validated by applying it to the evaluation of the stress triaxiality of high strength steel plates. Results show that the stress triaxiality and the fracture strains can be evaluated by the proposed method.

Evaluating Stress Triaxiality and Fracture Strain of Steel Sheet Using Stereovision

PROBLEM TO BE SOLVED: To provide a press molding manufacturing method for obtaining a desired shape more properly.SOLUTION: A press molding manufacturing method comprises: a step of arranging a pressed member 30 between a first mold 10 and a second mold 20; and a step of pressing a pressed part 31 so that the height of the pressed part 31 may be reduced by bringing the first mold 10 and the second mold 20 may be relatively moved to approach to each other. At the pressing step, a pair of first bent parts 31A bent to bulge toward the second mold 20 in the pressed part 31 are held by a pair of holding parts 20B disposed to leave each other at the pressed part 31. In the pressed part 31, a second bent portion 31B to be bent to bulge from the position between the paired firs bent portions 31A to the first mold 10 is pressed and deformed by the pressing part 14 of the first mold 10.SELECTED DRAWING: Figure 8

Press molding manufacturing method, press molding, and press molding apparatus

PROBLEM TO BE SOLVED: To provide a method of manufacturing a front body structure of a vehicle body, which enable weight reduction, can perform manufacture without introducing new equipment and can prevent occurrence of defective products of a suspension tower such as partial cracks.SOLUTION: Drawing or bending is applied to an aluminum alloy sheet 41, 51 to form a first intermediate shape body 43, 52 of a suspension tower 4. Drawing is applied to the first intermediate shape body 43, 52 to form a second intermediate shape body 45, 54 closer in shape to the suspension tower 4. The second intermediate shape body 45, 54 is finish-formed into the shape of the suspension tower 4. The completed suspension tower 4 is joined to a front side member 2 and an upper side member 3.SELECTED DRAWING: Figure 3

Junya Naito

Papers

Design optimization and application of hot-stamped B pillar with local patchwork blanks

Method for manufacturing press-molded product and press-molding device

Evaluating Stress Triaxiality and Fracture Strain of Steel Sheet Using Stereovision

Press molding manufacturing method, press molding, and press molding apparatus

Method of manufacturing front structure of vehicle body