Extension of U* Index Theory to Nonlinear Case of Load Transfer Analysis

2015 ◽  
Author(s):  
Khashayar Pejhan ◽  
Qingguo Wang ◽  
Christine Q. Wu ◽  
Igor Telichev
Keyword(s):  
Load Transfer ◽  
Index Theory ◽  
Design Tool ◽  
Load Path ◽  
Nonlinear Load ◽  
Index Value ◽  
Transfer Index ◽  
Static Conditions ◽  
Nonlinear Elastic ◽  
Load Transfer Analysis

Load transfer analysis has been proved to be an effective approach for designing light weight vehicle structures in last two decades. There are two main procedures for predicting the load path in a vehicle: The stress trajectory method and the U* index theory. The first approach has shown some shortcomings in dealing with geometrical irregularities. As a result, automotive industries have mainly applied the U* index as a design tool to study the load transfer behavior in the vehicle structure. The U* index, is an indicator for the load transfer in the structure, i.e. higher U* index value indicates more significant role in the load transfer process. So, the distribution of the U* index in the structure can be used to predict the main load path in the structure. Nevertheless, this foundation of this theory is based upon the linear elasticity equations and consequently, it has always been limited to linear elastic problems in static or quasi static conditions. Eradicating this limitation and extending the U* Index theory to nonlinear elastic problems is the main objective of this study. An extension to nonlinear criteria for U* index theory is proposed in this paper. It is shown, for the very first time, that the extended nonlinear load transfer index (U*NL) is a true measure for the load transfer in the structure in a nonlinear elastic problem.

Experimental Study of U* Index Response to Structural and Loading Variations

2015 ◽  
Author(s):  
Khashayar Pejhan ◽  
Qingguo Wang ◽  
Igor Telichev
Keyword(s):  
Load Transfer ◽  
Experimental Testing ◽  
Minimum Weight ◽  
Index Theory ◽  
Load Path ◽  
Stress Concentrations ◽  
Structural Variations ◽  
Design Modification ◽  
Testing Procedures ◽  
Load Transfer Analysis

Load transfer analysis tracks the path, on which the imposed load is being carried through the structure. Recently, vehicle structure designers have paid growing attention to this aspect of structural analysis for designing lighter vehicle structures that can efficiently carry the imposed loads with minimum weight. There are two main procedures for load transfer analysis in automotive engineering: 1) Stress trajectory method and 2) U* index theory. The former method faces some difficulties in following load path in structures with stress concentrations made by geometrical irregularities. As a result the U* index theory has been utilized more frequently in this area. This theory has shown exceptional capacities in following load transfer in the structure and has provided innovative tools for design modification in automotive industry. Although it can be shown mathematically that U* index quantifies the internal stiffness of the structure there has not been an experimental validation for that. Moreover, the term internal stiffness itself is not an easy concept to follow and it can be easily mistaken for the structural stiffness of the structure. As a result in the current paper two experimental testing procedures are presented to distinguish the internal stiffness, that can be quantified with U* index and the structural (conventional) stiffness of the structure. Through these experiments, for the first time, physical evaluation of U* index response to loading and structural variations can be performed.

Application of Load Transfer Index (U*) in Structural Analysis in Comparison With Conventional Stress Analysis

2014 ◽  
Author(s):  
Khashayar Pejhan ◽  
Christine Q. Wu ◽  
Igor Telichev
Keyword(s):  
Stress Analysis ◽  
Load Transfer ◽  
Structure Design ◽  
Stress Distributions ◽  
Load Path ◽  
Additional Information ◽  
Path Index ◽  
Comprehensive Information ◽  
Transfer Index ◽  
Load Transfer Analysis

The U* index has been used for load transfer analysis to show its capability in giving general awareness regarding performance of structure. Although U* index and stress values have been proven to be useful indexes as structure design criteria, a thorough comparison between conventional stress analysis and loads transfer analysis (based on U* index) is lacking. In this study, we evaluate load transfer behaviors of a parcel rack of multiple passenger vehicles under different loading conditions using the U* index. Then by demonstrating the unique capabilities of U* as an index for stiffness, it is shown that the load path concept can be combined with the stress analysis results to provide comprehensive information about the structure responses to loading. In addition to the agreement between stress analysis and the U* analysis, it is shown that U* can provide additional information about the structure response that stress analysis fails. Such information includes: interpreting high and complicated stress distributions in structure and detection of questionable stiffness in certain parts of structure. More importantly, the load path index U* can detect the area where significant changes in the structure stiffness occurs. Such information can be used as a guideline for structure design with the goal to reduce the weight while still keeping the structure integrity.

Load Transfer Index for Composite Materials

2015 ◽  
Author(s):  
Qingguo Wang ◽  
Khashayar Pejhan ◽  
Christine Q. Wu ◽  
Igor Telichev
Keyword(s):  
Composite Materials ◽  
Composite Structures ◽  
Load Transfer ◽  
External Loading ◽  
Load Path ◽  
New Paradigm ◽  
Linear Elastic ◽  
Transfer Index ◽  
Fundamental Equations ◽  
Load Transfer Analysis

Load transfer analysis is a new paradigm for lightweight vehicle design. U* index has been proved to be an effective indicator for the load path. The U* theory indicates that the external loading mainly transfers through the parts with higher U* values in the structure. However, the fundamental equations of the theory are based on isotropic, homogenous, and linear elastic assumptions for the materials. Consequently, U* index is inadequate for composite materials which are increasingly used in automotive structures. In this study, a new load transfer index for composite structures, U*O, is proposed for the first time inspired by the basic U* theory. The U*O index considers the composite material as orthotropic instead of isotropic and eliminates the limitation of the basic U*. The effectiveness of the new U*O index on load path prediction is demonstrated by a case study for a general Graphite-epoxy lamina. The U*O index is capable to evaluate the accurate load path for the composite specimen. By contrast, the basic U* analysis shows the incorrect results.

Experimental validation of the U* index theory for load transfer analysis

2017 ◽  
Vol 24 (3) ◽  
pp. 288 ◽  
Author(s):  
Khashayar Pejhan ◽  
Qingguo Wang ◽  
Christine Q. Wu ◽  
Igor Telichev
Keyword(s):  
Experimental Validation ◽  
Load Transfer ◽  
Index Theory ◽  
Load Transfer Analysis

Experimental validation of the U* index theory for load transfer analysis

2017 ◽  
Vol 24 (3) ◽  
pp. 288 ◽  
Author(s):  
Khashayar Pejhan ◽  
Igor Telichev ◽  
Christine Q. Wu ◽  
Qingguo Wang
Keyword(s):  
Experimental Validation ◽  
Load Transfer ◽  
Index Theory ◽  
Load Transfer Analysis

A New Cam-follower Safety Joint Mechanism Design based on Variable-length Four-bar Linkage for Robot Safety

2021 ◽  
pp. 1-24
Author(s):  
Seung Guk Baek ◽  
Hyungpil Moon ◽  
Hyouk Ryeol Choi ◽  
Ja Choon Koo
Keyword(s):  
Load Transfer ◽  
Impact Damage ◽  
Surface Profile ◽  
Length Change ◽  
Variable Length ◽  
Core Element ◽  
Nonlinear Load ◽  
Cam Follower ◽  
Joint Mechanism ◽  
The Impact

Abstract Humans come into physical contacts with various machines such as robots in daily life. This leads to the underlying issue of guaranteeing safety during such human-robot interactions. Thus, many devices and methods have been studied for impact damage reduction. A safety joint mechanism (SJM) using four-bar linkages has been highlighted as an impact cutoff device owing to its capabilities of nonlinear load transfer. This paper focuses on a new design and testing for a kinematic element of an SJM based on four-bar linkages to improve the impact cutoff performances. In the present work, a set of variable-length floating link designs is proposed, and the mechanism is implemented by mechanical contact surface profile shaping between the cams and followers. The performance of the cam-follower mechanism is evaluated depending on the variable length of the floating link, by using equivalent stiffness method, which successfully quantifies the performance of the proposed mechanism. Based on this design and analysis, two SJMs having symmetrical arrangements for four numbers of cam-follower mechanisms are fabricated: one SJM has fixed-length floating links and the other has variable-length floating links. The effect of the new kinematic elements on the performance improvement is verified by comparing the absorbed impact rates of the two SJMs by impact hammer-like drop tests. Consequently, it is confirmed that the rapid length change of the floating link is the core element for improving the performance of the safety mechanism.

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