Why Is It Important To Measure Wall Size Of Composite Electronics Enclosures?

Updated: August 24, 2016

Composite electronic enclosures have found widespread usage in the avionics and spacecraft industry. They are designed and manufactured to decrease the load, but do not utilize the directional traits of advanced composites mixed with the laminated design of the composite material. If directional strength and stiffness were considered during the analysis of the electronics enclosure, fewer plies would have sufficed for the walls. Modular design concepts, however, indicate  that they might assist in weight reduction,  incorporation of structural and thermal load paths when required, and finally add optical fiber signal-carrying facilities to the enclosed walls.

Why Are Wall Size Measurements Necessary?

Initial preparations would have benefited from the easy availability of texts on composites. Such texts would have supplied the necessary empirical or analytic equations on deflections and bending stresses, buckling allowables, natural frequencies and more for various structural components, thereby assisting in the preliminary sizing of the composite structure. Empirical or analytic equations would need to be present for various geometries in the text, but unfortunately, there is no such equation available for orthotropic or anisotropic materials.

Analytic solutions are not only hard to find, but their computation takes a lot of time and effort duet to the tensorial character of the stress-strain constitutive equations. Such calculations involve the multiplication, transformation and inversion of matrices. In case of orthotropic materials, the ply stresses are extremely difficult to compute due to the presence of coupling between the laminate loads and the dependence of ply stress on fiber orientation and the moments through the extension-bending coupling matrix. However, for rectangular composite electronics enclosures, the entire structure is reducible to plain rectangular panels. This means preliminary sizing is manageable by designing the panels as simple supported orthotropic plates. This sort of geometry has produced numerous analytic equations and so can be computed immediately. You can use a more comprehensive finite element analysis (FEA) for optimizing the thickness, thermal nature, ply orientation and weight.


Understanding the Scope of the Measurements

The main aim of taking measurements is basically to identify and employ empirical or analytic equations for sizing the walls of composite electronics enclosures. The walls should preferably be orthotropic laminated plates with simple boundaries. This will allow for the ideal computation of deflections, stresses, sheer buckling and uniaxial buckling, and natural frequencies allowables. The analytics solutions will then be compared to the standard results produced by the FEA for laminates with varying degrees of orthotropy. This sort of sizing technique and FEA when completed before the different stages of design, fabrication and testing allows for the creation of an electrical enclosure.

What Are the Important Techniques?

A regular card cage needs to be conceptualized and manufactured, incorporating the different benefits of composites minus the usual penalty of the non-recurring, high expenses of process development and tooling generally associated with unique aerospace composite. It is important to ensure that the composite card cage has a lower per copy cost than a similar machined card cage. Composites are used at an optimum level in the design mode which results in a reduced usage of parts, thereby preventing the occurrence of the “black aluminum” design syndrome. This is essential since it effectively guarantees that composites will not replace any aluminum.

Construction Components

Material: The material used in the construction of the advanced composite electronics enclosure should be carefully selected. It mus have low outgassing properties, low moisture uptake along with microcracking ability. This is available easily and you should not have any trouble finding it.

Fiber: The fiber you choose for the job is also extremely vital since it should possess heat-spreading capabilities along with thermal conductivity. Bear in mind that the fiber will be used in thermal plane and so dearth of these properties might damage the component.

Fabric: Choosing the right fabric for building the electronics enclosure is necessary. Not only should it be cost-effective, but must also possess good handling properties. Make sure that the fabric is widely available since this would aid in logistics.


The walls of the enclosure will first have to be sized as per specification and an FEA model will then be built. Random vibration loads will be imposed on the structure with the help of a Power Spectral Density (PSD) and they will curve independently in all of the three directions. The finished enclosure, if properly made, will pass any random thermal test that it is subjected to. Moreover, it should also successfully pass the different vibration tests and meet all the other important goals as well.

Structure of the Electronics Enclosure

An advanced composite electronics enclosure, upon completion, can be subdivided into various parts. It will be comprised of four separate walls as well as a bottom and a top. If the design suggests that the walls of the enclosure are triangular in shape, it is necessary to use balanced, symmetric, orthotropic plates. Most of the design equations are developed in such a way that the walls are initially sized upon consideration of the material, thickness and the layup. The deflections and bending stresses along with the shear and uniaxial buckling allowables, andthe vibrational modes are carefully calculated with the intention of accommodating three laminate configurations. The whole setup must then be compared to those that are produced using a finite element model with casually supported conditions in terms of the boundary. The actual materials used need to be a high-thermal conductivity (HMHTC) unidirectional pitch epoxy/fiber, a high strength-high modulus/ an intermediate strength-intermediate modulus (IMIS) carbon epoxy/fabric.

Quality Control

The Tsai-Wu failure criterion can be used for comparison of safety margins in the context of the analytic calculations with the ones that are gained from an FEA of the plate. The analytic predictions in all instances should always be on the conservative side, being predicted with lower safety margins.

The formation of the enclosure depends greatly on the analytic equations. These products have vital applications across different industries and so it is important that the measurements are taken with utmost care and precision. They help with determining the size of the advanced composite electronics enclosures modeled through FEA and tested successfully in random modes of vibration. Most experts recommend addressing shielding issues at the very onset, rather than integrating it after the completion of the design. This is a great way to cut cost and solve shielding anomalies later on. You may contact a solutions provider for further assistance.