## 1 Introduction
[26] conducted an in situ residual stress/strain investigation using MRCC and proposed two new cure cycles which ultimately reduced residual strain by 12-18% while tensile strength improved up to 26%. Extended manufacturer's recommended cure cycle (EMRCC) consists of an extra temperature dwell T\({}_{\text{B2}}\) after the first T\({}_{\text{B}}\). The drawback of EMRCC is it requires a relatively longer curing time compared to that of MRCC. Direct cure cycle (DC), on the other hand, raised T\({}_{\text{B}}\) closer to T\({}_{\text{C}}\). Samples produced using DC are reported to suffer from reduced tensile strength, despite an 18% improved residual strain when compared to those of MRCC. The modified cycles showed no significant changes in the void content. To date, the information on the effects of various bagging techniques for composites with complex shapes produced using these cure cycles are not readily available. Among bagging techniques, most conventionally used is a typical one bag setup which creates one vacuum environment, hereby referred to as single vacuum-bag-only (SVB) in this study. This technique is readily used for composites with flat or streamline structures [27]. However, SVB is vulnerable to thickness deviation in composite structures with blunt corners [28]. A modified single vacuum-bag-only (MVSB), also uses one bag to create a vacuum environment but it incorporates the use of metallic or polymeric intensifiers, caul-sheets or pressure strips in the corners of complex structures [29; 30; 31]. The bridging effect in complex shape structures, where laminates do not completely conform to the shape of the mold, is prevented by the use of an MSVB technique. Double vacuum-bag-only (DVB) uses two vacuum environments by using either a rigid chamber [32] or two bags (inner and outer bags), which are separated by an intermediate metallic perforated tool [33] to facilitate volatile depletion during B-stage. During low-temperature dwell, there is a pressure difference maintained between both bags to create a ballooning effect, i.e., 100 kPa for the outer bag and 95 kPa for inner bag. In this case, a pressure application of 100 kPa (which is the maximum pressure) is considered full vacuum, while pressure below 100 kPa is considered partial vacuum. DVB uses a partial pressure of 95 kPa in the inner environment while a full 100 kPa pressure in the outer environment during B-stage to create a ballooning effect inside the inner environment which consequently allows trapped volatiles to escape, also known as degassing phase. Whereas, the outer bag is purged to the atmosphere and a full vacuum is drawn in the inner environment for final consolidation, also referred to as the compaction phase [32; 33]. Unfortunately, the literature related to the adaptability, efficiency, and performance of the DVB technique to commercial and industrial applications is not readily available. Furthermore, their effects on the use of various curing profiles for composites with complex shapes are also not reported. There are several challenges in producing laminated composites with complex shapes. The most frequent concern is the thickness deviation of corner regions from that of the flange regions in complex-shaped laminates [29; 34]. The highest thickness gradients, either corner thickening or thinning, are said to be dependent upon the ply orientation and the curvature of the molds [35]. Manufacturing-induced defects can get worse with the increase in the part sizes and geometric complexity. Thickness variation refers to the thickness difference between corner region and nominal flange region thicknesses. Thickness uniformity in corner regions and flange regions is an accepted quality characteristic for laminates with complex shapes because it is easy to quantity [36; 37]. The main reason behind thickness variations in composites with complex structures is the difference in reaction pressure acting at the corner and the flange regions [36].