"composite effect" is correct and usable in written English.
You can use it when referring to an effect that is created by a combination of multiple smaller effects. For example: "We observed a dramatic composite effect on the environment after the changes were made to the irrigation system."
This general sort of "composite effect" sounds unspecific and blurry, enough to cast doubt on the findings.
This one is really a red flag: "this paper provides evidence of a composite effect" (combined air and water pollution) on infant health" (page 6).
An appropriate addition amount of FeS is important for the composite effect.
We propose a utility function to measure the composite effect of toxicity and efficacy and select the optimal dose.
The combination of steel fibres and stirrups demonstrates a positive composite effect on the mechanical behaviour.
The composite effect of sulfide layer and FeS particles possessed very good anti-scuffing and anti-wear properties.
The slab spatial composite effect plays a significant role in the behavior of composite frame structural systems subjected to lateral forces.
Our findings suggest that holistic processing, as measured by the composite effect, might be moderated by less efficient attentional control in children and older adults.
The detail of the connection was designed to prevent brittle failure at the bottom of the connection due to the composite effect and to simplify its fabrication process.
According to the test results, the spatial composite effect between the orthogonal steel beams and concrete slab significantly influences the performance of the SCCWFS.
The excellent mechanical properties of the alloy were attributed to the spinodal decomposition of BCC phases and the composite effect of the softer FCC and harder BCC phases.
