Emerging trends in manufacturing such as light weighting, increased performance and functionality increases the use of multi-material, hybrid structures and thus the need for joining of dissimilar materials. The properties of the different materials are jointly utilised to achieve product performance. The joining processes can, on the other hand be challenging due to the same different properties. This paper reviews and summarizes state of the art research in joining dissimilar materials. Current and emerging joining technologies are reviewed according to the mechanisms of joint formation, i.e.; mechanical, chemical, thermal, or hybrid processes. Methods for process selection are described and future challenges for research on joining dissimilar materials are summarized.

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Joining of dissimilar materials

Self-pierce riveting for sheet materials: State of the art

The stress intensities (notch stress, stress intensity factors and J-integral) at spot welds under typical loads of tensile-shear, cross-tension and coach-peel are derived as a number of simple formulas on the basis of an analytic solution where the stress intensities at spot welds are generally determined by the stresses around the spot welds and of some analytic solutions to circular rigid inclusions in plates with the inclusions simulating the weld nuggets. The derived formulas show consistently the trends in the stress intensities with the design parameters for spot welds such as nugget diameter and sheet thickness and additionally with spacing of force for cross-tension spot welds and load eccentricity for coach-peel spot welds. The stress intensities at spot welds under general loading conditions are estimated in terms of the forces and moments transferred by the spot welds based on the derivations. The theoretical predictions from the formulas are compared favorably with the finite element results. As an application example, some fatigue test data for spot welds in the form of load range versus life to failure are transferred into the form of stress intensities range versus life to failure with the scatterband of the fatigue test data being substantially reduced.

Stress Intensities at Spot Welds

Self-piercing riveting (SPR) is a cold mechanical joining process used to join two or more sheets of materials by driving a rivet piercing through the top sheet or the top and middle sheets and subsequently lock into the bottom sheet under the guidance of a suitable die. SPR is currently the main joining method for aluminium and mixed-material lightweight automotive structures. SPR was originated half century ago, but it only had significant progress in the last 25 years due to the requirement of joining lightweight materials, such as aluminium alloy structures, aluminium-steel structures and other mixed-material structures, from the automotive industry. Compared with other conventional joining methods, SPR has many advantages including no pre-drilled holes required, no fume, no spark and low noise, no surface treatment required, ability to join multi-layer materials and mixed materials and ability to produce joints with high static and fatigue strengths. In this paper, research investigations that have been conducted on self-piercing riveting will be extensively reviewed. The current state and development of SPR process is reviewed and the influence of the key process parameters on joint quality is discussed. The mechanical properties of SPR joints, the corrosion behaviour of SPR joints, the distortion of SPR joints and the simulation of SPR process and joint performance are reviewed. Developing reliable simulation methods for SPR process and joint performance to reduce the need of physical testing has been identified as one of the main challenges.

/pdf/self-piercing-riveting-a-review-2j1byq6md3.pdf

Self-piercing riveting-a review

Three-dimensional finite element analysis of the mechanical behavior of spot welds

The fatigue behaviour of single- and double-rivet aluminum alloy 5754-0 self-piercing riveted (SPR) lap joints has been investigated experimentally and analytically. With the single rivet, the experimental program involves a set of 27 cyclic tension tests on joints with 1-, 2- or 3-mm-thick sheet coupons. In most cases (85%), fatigue cracks are found to initiate in the gross section on the faying surface of the upper sheet. With two rivets (installed in two rows), the experimental program consists of nine cyclic tension tests, three for each of the three combinations of riveting orientation possible, on SPR joints consisting of2 -mm-thick sheet specimens. The fatigue life of double-rivet joints is found to be strongly dependent on the orientation combination of the rivets. Monotonic tests with the double-rivet joints also reveal an influence of orientation combination. In addition to experiments, values of local stress and rivet-sheet microslip in the single-rivet joints have been evaluated through three-dimensional elastic finite-element analysis. The analyses are used to interpret experimental observations of fatigue crack initiation location, life and fretting damage severity.

https://deepblue.lib.umich.edu/bitstream/handle/2027.42/75233/j.1460-2695.2005.00938.x.pdf;sequence=1

Fatigue of single- and double-rivet self-piercing riveted lap joints

Resistance spot welding is the most widely used joining method in automobile manufacture. The number, location, and quality of welds are some of the factors that influence the performance of welded subassemblies, and body panel structures. Therefore, design optimization requires knowledge of not only sheet metal behavior, but also weld behavior under service loadings. A linear elastic fracture mechanics approach was employed in this study to estimate the fatigue lives of spot welds subjected to tearing loads in a coach-peel specimen. Using a finite element method (FEM), the initial J-integral values for five coach-peel joints, each with different geometries, were calculated. Fatigue tests conducted on the same weld geometries provided life data. The experimental data were used to derive a relationship between the initial elastic J-integral values (ΔJe) and the fatigue life. It was found that the total fatigue life (Nf) of a weld at one applied stress range is related to its range of J-integral value such that a ΔJe vs Nf log-log plot gives a straight line relationship. This relationship can be used to evaluate the effects of geometrical variables on the fatigue life of coach-peel joints. The results show that, within the dimension range studied here, the effects of geometrical variables on the fatigue resistance can be ranked in the following decreasing order: weld eccentricity, sheet thickness and weld nugget diameter.

Fracture mechanics analysis of fatigue resistance of spot welded coach‐peel joints

A J-integral approach was used in this study to predict the fatigue lives of spot welds subjected to tensile-shear loads. Using a three-dimensional finite element program, J-integral values were computed for spot welds that reflect the overall weld stiffness

A J-Integral Approach to Fatigue Resistance of a Tensile-Shear Spot Weld

The fatigue life and fretting characteristics of aluminum alloy 5754-O self-piercing riveted lap joints have been investigated experimentally and analytically. The experimental program involves a set of 27 cyclic tension tests on three different joints consisting of either 1 mm, 2 mm or 3 mm-thick sheet specimens. In most cases (85%), fatigue cracks are found to initiate on the faying surface of the upper sheet, adjacent to the hole, and at an angular location that lies on the sheet loading axis towards the loading end. Three-dimensional finite element analysis of the three joints has also been performed. Computed distributions of local stresses and rivet-sheet slips are interpreted in terms of experimental observations of fatigue life, crack initiation location and fretting damage observations. Significantly, the calculations provide a rationale for the surprising crack initiation location.© 2002 ASME

Fatigue and fretting of self-piercing riveted joints

An enhanced head-and-neck restraint system is provided for use with a vehicle having a passenger compartment with a seat assembly and a safety belt assembly mounted therein. The restraint system includes first and second collar straps each having an inflatable cushion integrated thereto. A first end of each collar strap is attached to a headrest portion of the seat assembly to transition between a retracted position, in which the collar straps are substantially inside the headrest portion, and a use position, in which each collar strap attaches to a belt webbing of the safety belt system. A fluid dispensing apparatus is in fluid communication with the inflatable cushions, and operable to selectively transition the inflatable cushions from a non-expanded state to an expanded state when the collar straps are in the use position.

Pei-Chung Wang

Papers

Fatigue of single- and double-rivet self-piercing riveted lap joints

Fracture mechanics analysis of fatigue resistance of spot welded coach‐peel joints

A J-Integral Approach to Fatigue Resistance of a Tensile-Shear Spot Weld

Fatigue and fretting of self-piercing riveted joints

Retractable supplemental inflatable restraint system for vehicle head rest